Safety:

• Carry out a Toolbox meeting, Risk assessment and Permit to work.
• Ensure that the internal pressure of the boiler is fully relieved before attempting to remove the safety valve. Wear appropriate personal protective equipment (PPE), including safety glasses, to protect against residual fluid splashes.

Disassembly Steps:

• Remove the seal and pull out the split pin.
• Detach the fork lever.
• Loosen the set screw and remove the cap.
• Remove the spindle lock nut and adjusting screws from the spring cover (make a mark on the position of the adjusting screw and spring cover for easy reassembly).
• Take off the spring cover.
• Remove the nut connecting the yoke with the body, then lift the block composed of the yoke, upper spring, and lower spring carrier along with the spring.
• Pull out the spindle.
• Remove the disc.
• Loosen the screw and remove the valve seat.

Checks:

• Inspect the valve seat and disc for damage; lap if necessary.
• Check the sliding surface of the floating piston for dirt and foreign materials, cleaning thoroughly.
• Assess the condition of the spindle for trueness.
• Inspect the body for rust and corrosion.
• Examine the spring for cracks and measure its free length.
• Verify the working of the easing gear.
• Ensure the drain line is clear.
• Conduct non-destructive testing of components as needed.
• Check the condition of the blowdown ring and the compression ring neck bush.

Clearances to be measured:

• Measure the clearance between the valve lip and the seat lip.
• Clearances between spindle and cap nut
• Measure the clearance between the cotter pin and the groove in the spindle.
• Check the clearances between the floating piston and the spindle.
• Check the lift after assembly. It should be more than D/16 for high lift safety valve

1. Adjustment of Blowing-Off Pressure
2. Adjustment of Blowdown Pressure

Steps:

• Increase the steam pressure to about 20% below the intended blowing-off pressure.
• Ensure the main steam stop valve remains closed to prevent steam from entering other systems.
• A calibrated pressure gauge should be installed to ensure accurate readings.
• Have gagging tools handy for use during the adjustment.
• The person adjusting the valve should wear proper PPE to ensure safety.
• Check the operation of the safety valve by using the easing gear, which ensures all valve parts are near working temperature when the valve lifts.
• Disassemble the easing gear, including the cap nut and cotter pin.
• Gag the other safety valve to isolate it from the system.

Initial Adjustment:

• Check the position of the compression screw and loosen it slightly to remove the compression ring.
• Tighten the screw by one or two turns to increase the spring load.

Blow-Off Pressure Setting:

• Gradually raise the steam pressure. As the blow-off pressure approaches, slowly unscrew the adjusting screw until a hissing sound is heard, followed by the valve lifting.
• Record this pressure, which is the approximate blow-off pressure.

Blowdown Pressure:

• Reduce the boiler firing rate to a minimum. When the valve reseats, it will do so at a pressure lower than the blow-off pressure. This is the approximate blowdown pressure.
• The blowdown pressure can be fine-tuned by adjusting the blowdown ring, usually 5% lower than the maximum working pressure.

Final Adjustments:

• Recheck the blow-off pressure by increasing the firing rate to ensure accuracy. Make adjustments as needed.
• Once set, reinstall the compression ring and verify that it is properly secured between the compression screw and neck bush on the valve top cover.
• Repeat the same procedure to set the second safety valve.

Easing Gear Check:

• After both valves are set, reconnect the easing gear and ensure it operates safely.

• Measure the distance between the lower face of the compression nut and the upper face of the column cover plate of the yoke.
• Measure the size of the compression ring for future reference.
• Reassemble the easing gear and confirm that it operates correctly.
• Secure the valve settings by placing a lock to prevent any unauthorised tampering with the settings.
• Prepare a detailed report including:
  • Blow-off pressure
  • Blowdown pressure
  • Width of the compression ring
  • Date and signature of the person responsible for the adjustments.
• Obtain the signature of a surveyor to validate the safety valve setting.
• Send a copy of the report to the office.
• Keep the original report in the ship’s records for future reference.

(ii) Overheating of the pump drive shaft bearings is prevented by using the shaft housing (which also acts as a cargo riser) to cool and lubricate the bearings.

• Continuous boil-off gas reliquefaction
• Relief valves to release excess pressure
• Inert gas blanketing of the cargo hold; and
• If cargo hold is considered as secondary barrier, then if primary barrier/ cargo tank leaks then the flammable gas should not get oxygen to from an explosive mixture. So cargo hold is inverted.

The hunting gear in an electro-hydraulic steering system acts as a feedback controller responsible for maintaining the rudder's position. It achieves this by continuously comparing the desired rudder position (setpoint) received from the wheelhouse with the actual rudder position.

In control parlance, it operates as a closed-loop control system with the following functions:

• The hunting gear receives two input signals: The desired rudder position (set by the wheelhouse control) and The actual rudder position (measured by the rudder’s current position). It compares these signals to detect any error or difference.
• An error signal is generated if there is a difference between the desired and actual rudder positions. This signal causes the pump actuating lever to move, which adjusts the oil flow to the hydraulic cylinders, thereby correcting the rudder’s position.
• As the rudder moves to the desired position, the floating lever of the hunting gear also moves, feeding the corrected position back into the system.
• When the rudder reaches the desired position, the pump returns to the neutral position (no stroke), stopping the oil flow and keeping the rudder steady.
• If external forces, like waves, cause the rudder to deviate, the hunting gear will automatically detect the deviation and make corrections by adjusting the pump, similar to a controller in a closed-loop system.

The below sketch shows the operation of hunting gear.

• When the telemeter control receives the order for any movement from the wheelhouse, it moves one end of the floating lever to either side, depending upon the order. So it moves from position A to A’ as shown in the above sketch
• Movement of the floating lever will cause pump actuating lever to move from B to B’. This will start the pumping of oil and thereby the movement of rams.
• Once the rudder has accrued its desired position, it also moves the free end of floating lever to a new position i.e. from C to C’
• This movement of C to C’ will bring back the pump actuating lever to its original position i.e. from B’ to B. Thus, the pump is at no-stroke/ neutral position, causing the rudder to stay at its position.

If the standby pumping unit is motored, it means that the standby pump is rotating in the opposite direction to the operating pump, driven by the pressure generated by the operating pump. The following consequences may occur:

• Reduced Efficiency: The operating pump's output energy is wasted in rotating the standby pump, leading to reduced efficiency and slower rudder response.
• Motor Failure: The standby pump motor is designed to rotate in one direction. Running it in reverse can damage the ball bearings and ultimately lead to motor failure.
• Hydraulic System Instability: The opposite rotation of the pumps can introduce instability in the hydraulic system, leading to unpredictable rudder behaviour.

• Mechanical Locking: This method utilises a ratchet and pawl mechanism. The stationary ratchet is fixed with the motor casing while the pawls are mounted along with the pump coupling. When the pump is running, the pawl flies outwards due to centrifugal force and makes contact with the casing, which revolves with the coupling. When the pump stops, the pawls return to their normal position and engage with the ratchet teeth, thereby providing a positive lock against reverse rotation.

• Hydraulic Locking: This method uses a hydraulically operated bypass valve. While the pump is running, the bypass valve is closed due to hydraulic pressure from an auxiliary pump. When the pump stops, the pressure drops, causing the valve to open due to spring force. This blocks any oil flow from the operating pump to the standby pump, preventing it from motoring.

• Compressing air generates heat, and intercoolers reduce the temperature of air before it enters the next stage, protecting components from heat damage.
• Cooler air requires less work for compression in subsequent stages, improving overall efficiency.
• By lowering operating temperatures, intercoolers reduce thermal stresses on components, enhancing durability.
• Cooling condenses moisture in the air, preventing water accumulation in downstream equipment.

To Keep Intercoolers safe and in good working condition:

• Ensure a continuous supply of cooling water.
• Regularly clean the intercooler to maintain efficient heat exchange.
• Drain accumulated oil and water frequently.
• Verify that the intercooler drain line is clear.
• Inspect and maintain the bursting disc to prevent failure under excessive pressure.

The sketch depicts a multi-tubular intercooler suitable for a 2400 kPa compressor. It uses a shell-and-tube design. The compressor's high-pressure air flows through numerous small-diameter copper tubes, maximizing the surface area for heat exchange. Cooling water circulates around the tubes in a cast iron jacket, absorbing the heat from the compressed air. A copper or brass bursting disc serves as a safety pressure relief device.

Materials Used:

• Body: Cast iron (provides strength and corrosion resistance)
• Tubes: Copper (excellent thermal conductivity)
• Bursting Disc: Copper/Brass/Steel (depending on pressure requirements)

• Ensure the electrical circuit is switched off and tagged with "Men at Work."
• Fully drain the compressor, intercoolers, and air receivers to release residual pressure.
• Verify that the discharge valve is not leaking air into the system.
• Remove dirt and debris from around the compressor to prevent contamination during inspection.
• Allow the compressor to cool if it has been in operation to prevent burns or thermal stresses.
• Wear appropriate personal protective equipment (PPE), including safety glasses, gloves etc, depending on the conditions.

Likely faults and remedy:

The most effective way to prevent faults and ensure long-term reliability is through a rigorous preventative maintenance schedule (PMS) – including regular inspections, cleaning, component replacements, and lubrication as per the manufacturer's recommendations.

Maintenance Recommendations:

• Overhaul suction and discharge valves every 1000 hours.
• Replace air filters every 500 hours.
• Inspect and test relief valves every 4000 hours.
• Check IR for motor windings every 2000 hours.
• Change lubricating oil every 2500 hours.

Oil-Lubricated Stern Bearing System

The primary method for preventing seawater ingress into an oil-lubricated stern bearing system is a combination of mechanical seals and maintaining a balanced oil pressure. The system uses lip seals to contain the lubricating oil within the stern tube. An oil header tank ensures the oil pressure inside the stern tube is approximately equal to the surrounding seawater pressure. This balanced pressure prevents seawater from entering the stern tube.

Corrective Actions While Afloat

If the stern bearing system fails and seawater begins to ingress, the following temporary corrective actions can be taken while the vessel is still afloat:

• Switch to High-Viscosity Oil: The system can be recharged with a higher-viscosity oil. This thicker oil is less likely to leak past the seals, reducing the rate of seawater ingress.
• Install a Temporary Header Tank: Disconnect the regular oil supply line and connect a 45-gallon drum. This drum, supported by a block and tackle, acts as a temporary header tank with a variable head. The height of the drum can be adjusted by raising or lowering it to match the seawater pressure, ensuring the correct pressure balance is maintained.

Why Two Stern Bearing Oil Header Tanks Are Fitted

In some cases, two stern bearing oil header tanks are fitted, especially on vessels that experience large variations in draft, such as tankers. The two tanks are installed at different heights to accommodate these draft changes.

• The purpose is to match the oil pressure to the changing seawater pressure as the vessel's draft changes.
• By having tanks at different heights, the crew can switch between them to maintain the necessary differential pressure to keep seawater out of the stern tube. The maximum allowable pressure difference between the seawater and the oil is typically 0.3 bar.
• For example, the changeover between the tanks is often done at a specific draft, such as 11.7 meters.

Modern ships often use a single header tank with an air pneumatic system. This system automatically adjusts the oil pressure to match the seawater pressure based on the vessel's draft, eliminating the need for manual checks and tank changes.

(a) Impingement attack is a form of material degradation resulting from the erosive action of high-velocity fluid impacting a surface. The high-velocity fluid flow creates localised zones of high stress and turbulence, leading to material removal. The most susceptible locations for impingement attack are:

• Tube bends: High-velocity flow changes direction, leading to material erosion.
• Tube entrances: Sharp fluid acceleration causes localized erosion.
• Heat exchanger shell in front of fluid entrance: Direct impingement of the incoming fluid can damage the shell.
• Baffle plates: The deflection of fluid flow by baffles causes turbulence and erosion.
• Openings like vents and drains: Concentrated flow in these areas increases erosion risk.

$$Q\:=\:\frac{A\:\times K\times\Delta T}{X}$$

Where,

• Q is the heat transfer rate,
• A is the area,
• K is the heat transfer coefficient,
• ΔT is the temperature difference, and
• x is the tube thickness.

• From the above equation, it is clear that the heat transfer is directly proportional to the mass flow rate.
• If the flow rate is increased, the rate of heat transfer will increase.
• But this will also increase turbulence and pressure drop which will lead to impingement corrosion.
• Therefore it is desirable to keep the flow rate within limits to maintain the fluid temperature.

• Well-shaped water boxes promote even flow distribution, reducing localized high-velocity zones that are conducive to impingement. Minimizing turbulence in the coolant minimizes the risk of erosion and corrosion.
• Smooth tube inlets minimise flow disturbances at the tube entrance, reducing the impact force on the tube material and decreasing the likelihood of impingement damage. A smooth transition into the tube reduces the risk of localised erosion.

• Obstructions reduce heat transfer efficiency, leading to uneven thermal distribution (overheating or undercooling) and potential tube damage.
• Deposits or obstructions increase frictional resistance, resulting in a pressure drop across the heat exchanger. This causes localized erosion, corrosion, and eventual tube failure.

• R-134a: Suitable for medium and high-temperature applications, serving as a long-term replacement for R-12.
• R-404A: Suitable for low and medium-temperature applications.
• R-407C: A replacement for R-22, suitable for medium and high-temperature applications.
• R-410A: Twice as efficient as R-22 but generally recommended for new systems only.

During Normal Operation:

• Implement a robust monitoring system with daily logs of key parameters to allow for early detection of any anomalies, such as pressure drops or temperature fluctuations, that might indicate a leak.
• Regular Leak Detection: Conduct routine leak tests to identify leaks from joints, seals, gaskets, pipes, and other components.
• Safety Valve Management: Ensure correct setting and operation of safety valves to prevent accidental refrigerant release.

During Maintenance Activities:

• Mandate the complete recovery and recycling of refrigerant gas before any maintenance work commences. Utilize onboard recovery systems, ensuring they are properly maintained and calibrated.
• Implement procedures to minimize refrigerant venting during maintenance, utilizing capturing and recovery techniques wherever possible.
• Provide comprehensive training to all maintenance personnel on proper handling, recovery, and recycling procedures for refrigerants.
• Maintain a clean, dry system to prolong mechanical seal effectiveness and prevent leaks. Avoid excessive water pressure in the condenser to prevent tube failures. Monitor machinery vibration to prevent damage that could lead to gas leaks.
• Use leak-proof connections for charging and recovery, employing compatible and manufacturer-specified gaskets and mechanical seals. Ensure all refrigerant is recovered before opening the system for maintenance.
• Use geniune Spare parts to avoid any failure of system leading to accidentally release of gas.

Brinell Hardness Test: This Test determines the hardness of a material by measuring its resistance to indentation.

Testing method:

• A hardened steel or tungsten carbide ball of diameter (D) is placed on the material's surface.
• A test load (F) is applied to the ball for a predetermined time.
• After removing the load, the diameter of the impression (d) is measured using a specialized microscope.

The Brinell Hardness Number (BHN) is calculated using the formula:

$$BHN \space = \space {{2F} \over \pi D (D - \sqrt{D^2 - d^2})} $$

where:

• F = Applied load in kgf
• D = Ball diameter in mm
• d = Diameter of the indentation in mm

Advantages:

• Provides an accurate measure of hardness.
• Particularly useful for testing materials with rough surfaces.

Limitations:

• Leaves a permanent impression on the material.
• Requires optical measurement of the impression diameter, which can be challenging.

1. Liquid Penetrant Inspection (Non-Destructive Test)

There are two different types, such as:

In the Fluorescent Dye method, after applying Dyes and viewing under ultra-violet light, any fault can be found by the glow of the penetrant in them.

In the Aerosol Dye method, the first cleaning bottle is applied on the surface for cleaning purposes and the second bottle of Dye follows to soak and enter into any flaws or cracks. Afterwards, the last bottle of Developer (or chalky sediment) is applied to reveal any faults on the component under test.

The liquid penetrant process is comparatively simple as no electronic system is involved, and the equipment necessary is cheaper than that required for other N.D.T systems. The major limitation of this method is that it can detect surface breaking only. The method is not suitable for use with naturally porous materials such as unglazed ceramics.

2. Ultrasonic testing (Non-Destructive Test)

The probe of the test equipment transmits high-frequency sound waves about 0.5 MHz to 20 MHz, which are reflected by any flaws in the object, and these reflected sound waves are then displayed on the monitor screen of the cathode ray oscilloscope.

Ultrasonic tests are suitable for the detection, identification and size assessment of a wide variety of both surface and sub-surface defects in materials.

The ultrasonic method can be used to measure the thickness of the material or to detect internal or surface defects in welds, casting or forging either during manufacture or when in service.

Conditions that Promote Microbial Growth:

• Presence of water
• Availability of nutrients
• Favourable temperature (25-40°C) and pH (8-9)
• Oxygen (depending on the type of microbes)

Indications of Microbial Degradation:

• Rotten egg-like smell due to gas production
• Slimy oil appearance, often with peeling paint inside the crankcase
• Black staining on white metal bearings, pins, and journals
• Excess water and sludge accumulation after purification
• Frequent filter plugging
• Corrosion on unprotected surfaces

Sources of Microbial Contamination:

• Distillate fuel
• Lube oil itself
• Cooling systems, bilge, retention tanks, and ballast tanks
• Contaminated bunkered oil

Effects of Microbial Degradation:

• Corrosive damage to bearings and journals due to acid production
• Increased water content in the oil, challenging to remove by purification
• Filter blockages and restricted flow
• Deterioration in oil properties, such as viscosity and pH
• Reduced heat transfer in coolers

Prevention of Microbial Degradation:

• Regular draining to avoid water accumulation
• Maintain ideal temperature conditions to inhibit microbial growth
• Avoid water contamination in the oil
• Regular testing and correct operation of purification systems
• Use biocides or fungicides, as recommended by oil suppliers

1. Always use the same sampling location, ideally in the main supply line just before the entry to the main engine.
2. Drain a sufficient amount of oil before collecting a sample.
3. Rinse the new container with oil before collection.
4. Draw samples only after the engine has been running at normal operating conditions.
5. Fully seal and label the sample with the date, vessel name, running hours, oil grade, and sampling point identification.

(c) Abnormal Water Content: High water content indicates water ingress into the system, potentially due to leaks in piston cooling pipes, heat exchangers, or cylinder liners, or purifier malfunction.

Action:

• Locate and repair the source of the water ingress.
• Drain the water after allowing sufficient time for settling.
• Use the purifier to remove remaining water and contaminants.
• Consider batch purification for more thorough cleaning.

Abnormal TBN (Total Base Number): Low TBN suggests the oil's alkalinity is depleted. This can be caused by water ingress or microbial contamination.

Action:

• Remove contaminants through purification.
• Depending on the severity, replenish or completely renew the oil. Consider the potential need for a complete oil change if the contamination is severe.

The pneumatic relay operates on the principle of a nozzle-flapper arrangement. Air supply pressure acts on a diaphragm located below a spring. A rod and plug, connected to the diaphragm, control the flow of output air through a nozzle. A flapper is positioned near the nozzle.

Operation:

1. An input signal (which can be a change in pressure or displacement of the flapper) affects the flapper's position.
2. Flapper movement changes the distance between the flapper and the nozzle. A decrease in distance (flapper closer to the nozzle) restricts the output airflow. Conversely, an increase in distance increases output airflow. This is the direct action of the relay.
3. Changes in the output air flow alter the back pressure at the nozzle.
4. Increased nozzle back pressure pushes the diaphragm downwards, compressing the spring and further reducing the output airflow. Decreased nozzle back pressure allows the spring to push the diaphragm upwards, increasing output airflow.
5. A portion of the output air is fed back through a line connected to a bellows and a feedback-adjusting spring (as shown in the sketch). This feedback pressure acts against the diaphragm, opposing the effect of the input signal. The bellows and spring arrangement allow the system to fine-tune the feedback strength. This negative feedback stabilises the system and increases the control range, preventing excessive overshoot or oscillation. The feedback mechanism subtracts from the effective input pressure, acting as a negative feedback loop.

According to SOLAS chapter - 2, part 1, regulation 29.16, every tanker of more than 10,000 GT shall comply with the following:

• The main steering capability due to a single failure in any part of one of the power actuating systems shall be regained in not more than 45 seconds.
• The main steering shall comprise at least two identical power actuating systems, each capable of meeting the requirements. Loss of fluid from one system shall be capable of being detected, and the defective system shall automatically get isolated so that the other system shall remain fully operational

Considering the above regulatory requirements, given below is a “Fail Safe steering gear” suitable for use on a tanker of more than 100,000 T DWT.

Shown in the diagram is a “Fail safe steering gear” having two independent power actuating systems that can

• Work simultaneously in normal operation, meeting the requirement OR
• Work independently and meet the requirement
• In the event of loss of fluid from any one system, it can be detected and isolated automatically so that the other system can remain fully operational.

Working:

• The system incorporates two sets of electric-driven pumps. Both main and auxiliary pumps are on the same shaft. The main pump shown in the diagram is a variable delivery pump
• The variable delivery pump takes suction from the tank and supplies hydraulic oil to the ram cylinders. The oil flow of the pump is determined by the pump actuating lever
• The movement of the pump actuating lever is controlled by the rudder angle order given by the bridge with the help of a bi-directional control valve
• A two-way shock relief valve is fitted between the two cylinders to release the pressure from one side of the cylinder to the other side in case of pressure increase in one of the cylinders due to heavy seas
• By-pass valves are also fitted between two cylinders, which are normally shut during operation. When one system is stopped, there is a pressure drop, as the auxiliary pump has also stopped this opens the by-pass valves, thus removing the hydraulic lock of the ram operation.
• Auto isolation valves in the system are there to isolate one system in case of any failure.

Sequence of events during hydraulic oil leak:

Case 1: Consider an oil leak from any pipe for cylinders 1 and 2 with the No. 1 pump running:

1. No. 1 tank level will come down to L1, and it will sound an alarm on the bridge and in ECR
2. When the tank level further drops to L2, i.e. low-low level, the no. 1 pump stops.
3. Stopping the No. 1 pump also stops the attached auxiliary pump. So the line pressure drops, due to which the normally closed by-pass valves ‘X’ and ‘Y’ open.
4. Simultaneously, the auto isolation valves ‘A’, ‘B’ and ‘C’ will be operated by an electric signal. A, B and C are normally open valves. The electric signal will close them. So, systems 1 and 2 will be completely separated. Thus, the defective system, I.e. system 1, is isolated.
5. Along with the operation of the auto isolation valves, the No. 2 pump will start automatically. The attached auxiliary pump will act on the by-pass valve ‘Y’ and close it. This enables cylinders 3 and 4 to be in normal operation.
6. It should also be noted that since system 1 is completely isolated, there is no oil pressure to operate the bypass valve. So the by-pass valves remain open, thereby removing the hydraulic lock for the ram movement in cylinders 1 and 2

Case 2: Consider an oil leakage from any pipe of cylinders 3 and 4 with the No. 1 pump running:

Points 1, 2 and 3 are the same as case 1

1. Simultaneously, the auto isolation valves ‘A’, ‘B’ and ‘C’ will be operated by an electric signal. This will shut the normally open valves A, B and C. Thus, systems 1 and 2 will be completely separated
2. Along with the operation of auto isolation valves, the No. 2 pump will start automatically. The attached auxiliary pump will act on the by-pass valve ‘Y’ and close. So, cylinders 3 and 4 will come into normal operation.
3. Now, since the leak is between the pipe of cylinders 3 and 4, the level of the no. 2 tank will drop to L1 and give an alarm.
4. The level will further drop to L2, but the pump will not stop and changeover to ensure that the leak is from the pipe of cylinders 3 and 4
5. When the no. 2 tank level drops to L3, the no. 2 pump stops and the no. 1 pump starts to operate the steering using cylinders 1 and 2
6. Starting the no. 1 pump will ensure that the by-pass valve ‘X’ is shut, and stopping the no. 2 pump will ensure that the by-pass valve ‘Y’ is open

This ensures the operation of the steering Gear with the defective system fully isolated.

A coil-operated brake for winches and deck machinery is designed to automatically adjust the braking force in response to changes in the load on the mooring line. This system ensures the correct force is applied between the brake band and the winch drum at all times.

The core principle is that when an additional load is applied to the mooring line, the line stretches, which in turn loosens the tightening mechanism. This loosening action automatically causes the brake to apply the correct force, maintaining constant tension. This has the significant advantage of being a self-adjusting system, meaning that once it's set, there's no need for a crew member to periodically re-apply the recommended torque. The brake is typically released using a hydraulic lever.

When a vessel is riding at anchor, a mechanism is used to lock the anchor chain and relieve the windlass of the strain. This is crucial for preventing damage to the windlass and ensuring the anchor is securely held.

A Cable stopper, often a pawl of a rod, is engaged with a link of the anchor chain. The pawl acts as a stop, preventing the chain from moving. All the weight and force from the anchor and the vessel's movement are then transferred to this locking device and the ship's structure, effectively relieving the windlass of any strain.

As Second Engineer, I would oversee the extensive welding repairs required for the vessel's rudder using the following plan:

Manual Metal Arc Welding (MMAW), also known as Shielded Metal Arc Welding (SMAW), is the most suitable process for this repair. The reasons are threefold:

• MMAW is highly portable, allowing for on-site repair within the drydock. The process is adaptable to various welding positions (downhand, overhead, horizontal, vertical) – a necessity given the complex geometry of a rudder.
• Assuming the rudder is constructed from standard steel, MMAW using readily available flux-coated electrodes provides good control, arc stability, and penetration. The flux coating protects the weld pool from atmospheric contamination during cooling.
• MMAW requires relatively simple equipment and is less demanding in terms of operator skill compared to other processes like TIG or MIG. This translates to cost-effectiveness and allows for a wider pool of qualified welders.
• If cast steel components are present, pre-heating will be necessary to minimize stress cracking, and specialized electrodes suited for the specific cast steel grade must be selected.

During welding by the metal arc process, the following points must be observed:

• Electrode Consumption Rate
• Penetration
• Slag Control
• Arc Length and Sound

1. Undercut: A groove formed along the edge of the weld bead, weakening the joint. Caused by excessive current, incorrect electrode angle, excessive travel speed, or improper electrode manipulation.

2. Overlap: Molten weld metal flows over the parent metal without proper fusion. Caused by low current, slow travel speed, excessive arc length, or improper joint preparation.

3. Slag Inclusion: Trapped slag within the weld metal, reducing its strength and potentially causing cracking. Caused by insufficient cleaning between passes, incorrect current, long arc length, slow travel speed, or too large an electrode diameter.

4. Incomplete Penetration: The weld does not fully fuse the joint faces, resulting in a weak joint. Caused by insufficient current, incorrect joint preparation (too small a root gap or bevel angle), excessive travel speed, or too large an electrode diameter.

• A thorough visual examination of all welds to identify any surface defects like cracks, porosity, or lack of fusion.
• NDT methods such as Magnetic Particle Inspection (MPI) or Dye Penetrant Inspection (DPI) will be employed to detect subsurface flaws that may not be visible during visual inspection. The specific NDT method chosen will depend on the type of steel and the accessibility of the weld areas.
• The repaired rudder will undergo a hydrostatic pressure test. This involves filling the rudder with a water head of 2.46 meters and observing for any leaks. This confirms the watertight integrity of the welds and the overall rudder structure.

Controllable Pitch Propellers (CPP)

It is preferable to house the main servomotor for a controllable pitch propeller (CPP) in the propeller hub rather than in the shafting forward of the propeller shaft. This design, known as a hub servo system, is preferred over the external servo system, which uses a long push-pull rod extending from the engine room. The primary reason for this preference is that the long push-pull rod in an external servo system is prone to bending. This bending can occur due to the rod's length and the significant water pressure acting against the propeller blades, which can compromise the pitch control mechanism's reliability and precision. Housing the servomotor directly in the hub eliminates the need for this long rod, resulting in a more robust and reliable system.

1. Hydraulic System Maintenance

• Periodic cleaning of hydraulic filters and oil coolers.
• Regular oil sampling (both onboard quick checks and shore analysis) to detect contamination or wear particles.
• Monitoring oil consumption to detect leaks in the system.

2. Mechanical Components

• Greasing all linkages to prevent corrosion and wear.
• Checking and lubricating moving parts as per manufacturer’s recommendations.

3. Operational Checks

• Ensuring familiarization of all relevant personnel with correct operating and maintenance procedures.
• Regular testing of alarms and safety devices.
• In dry dock, verify actual pitch position against remote indicators at the wheelhouse and engine room.
• Test the fail-safe arrangement to ensure it operates correctly in emergencies.

Pump rooms on tankers are required to be mechanically ventilated. The ventilation system must be of the exhaust type and designed to prevent the accumulation of flammable vapors. To ensure this, the system needs to have a minimum capacity of 20 air changes per hour based on the gross volume of the space. The exhaust fans must be a non-sparking type, and the air ducts should be arranged to provide effective ventilation throughout the entire space. The discharge from the exhaust fans must be led to a safe location on the open deck.

Cargo Tank Ventilation

Cargo tanks are ventilated to make them "gas free," which means removing flammable or toxic vapors. This can be achieved using portable fans or blowers. These fans must be constructed to prevent incendiary sparking, for example, if the impeller were to touch the casing. The fans must also have sufficient capacity and penetration to quickly gas-free the entire tank atmosphere.

Alternatively, on tankers equipped with an Inert Gas System (IGS), the system itself can be used for ventilation. To do this, the connection from the scrubber tower is closed, an air inlet from the atmosphere is opened, and the IGS blowers are started. This process effectively ventilates the cargo tanks by drawing in fresh air and pushing out the existing atmosphere.

The primary problem with carrying LNG is maintaining its extremely low temperature of approximately -160°C. Despite the insulated tanks, a small amount of the LNG will inevitably vaporize, a phenomenon known as "boil-off." This boil-off must be managed, as it poses a safety risk and represents a loss of cargo. The process of managing this boil-off is critical and consumes a significant amount of power if the gas is to be reliquefied.

Several methods are used to handle boil-off gas on board LNG carriers:

• Reliquefaction: Heavy-duty compressors are used to compress the boil-off gas, converting it back into a liquid state and returning it to the cargo tanks.
• Mixed Refrigeration: A refrigeration process that uses a mixture of different refrigerants to cool and reliquefy the boil-off gas.
• Expander Cycle: A method that uses an expander to cool the boil-off gas, causing it to reliquefy.
• Using it as Fuel: The boil-off gas can be used as fuel for the ship's engines, either completely or as a partial fuel in a dual-fuel combustion system. This turns a potential problem into a source of power for the vessel.

Leakage of treated boiler water (through a leaking blowdown pipe, valve, water tube, or circulating pump) and excessive blowdown both lead to a loss of treated water. Replacing this lost water with untreated makeup water dilutes the TDS and chemical reserves.

Action:

• Inspect all boiler blowdown pipes and valves for leaks and repair as necessary.
• Check for leaks in water tubes (indicated by white smoke from the funnel). Repair any leaks found.
• Inspect circulating pumps for leaks and repair as necessary.
• Once leaks are repaired, add chemicals to restore the desired levels.
• Monitor boiler water conditions through frequent testing.

(ii) Reduction in phosphate reserve, with an increase in chlorides and total dissolved solids:

Seawater ingress is the likely culprit. Seawater contamination introduces carbonates, sulfates, and chlorides of sodium, calcium, and magnesium. These ions react with phosphate in the boiler, forming non-scale sludge, leading to reduced phosphate reserves and increased chlorides and TDS.

Action:

• Identify and plug any leaky condenser tubes causing seawater ingress.
• Inspect and replace sacrificial anodes if necessary. This helps prevent corrosion.
• Increase the frequency and duration of boiler water blowdown.
• If chloride levels remain high, reduce boiler load to 2/3 normal output, blow down to minimum level, and refill with fresh make-up water.
• A complete emptying and flushing of the boiler is the ultimate solution to remove the remaining contamination. Carry out this at the earliest opportunity.

(iii) Reduction in alkalinity reserve only:

• Seawater contamination potentially introduces acidic products that neutralize the alkaline reserve.
• Boiler water leakage (loss of alkaline water).
• Oil contamination (oil can react to reduce alkalinity).
• Ingress of air (air can lead to the formation of acidic products that neutralize alkalinity).

Actions:

• Identify and rectify any seawater ingress.
• Maintain a high hotwell temperature to prevent air ingress.
• Identify and repair any boiler water leaks.
• Identify and eliminate the source of oil contamination.

(iv) Increase in oxygen levels only:

• Poor performance of the de-aerator, allowing oxygen to remain in the feedwater.
• Insufficient hydrazine reserves (hydrazine is an oxygen scavenger).
• Low hotwell temperature (oxygen is more soluble in colder water).
• Leaking feed water pump gland (allowing air to enter).

Actions:

• Inspect and repair any faults in the deaerator.
• Ensure adequate hydrazine reserves are maintained.
• Maintain a high hotwell temperature.
• Identify and repair any gland seal leaks in the feed water pump.

• Complete data allows for the identification of subtle trends indicating developing problems. A gradual decrease in alkalinity, for example, might not immediately exceed the alarm threshold but could signal a developing issue that can be addressed proactively.
• Comparing current results to past results helps establish a baseline and allows for easier detection of anomalies.
• Complete data provides more context during troubleshooting. If a problem arises, having access to a complete history can help identify the root cause more effectively.
• Logged data enables proactive adjustments and repairs before faults escalate, preventing boiler damage and reducing unplanned downtime.

• R-134a: Suitable for medium and high-temperature applications, serving as a long-term replacement for R-12.
• R-404A: Suitable for low and medium-temperature applications.
• R-407C: A replacement for R-22, suitable for medium and high-temperature applications.
• R-410A: Twice as efficient as R-22 but generally recommended for new systems only.

During Normal Operation:

• Implement a robust monitoring system with daily logs of key parameters to allow for early detection of any anomalies, such as pressure drops or temperature fluctuations, that might indicate a leak.
• Regular Leak Detection: Conduct routine leak tests to identify leaks from joints, seals, gaskets, pipes, and other components.
• Safety Valve Management: Ensure correct setting and operation of safety valves to prevent accidental refrigerant release.

During Maintenance Activities:

• Mandate the complete recovery and recycling of refrigerant gas before any maintenance work commences. Utilize onboard recovery systems, ensuring they are properly maintained and calibrated.
• Implement procedures to minimize refrigerant venting during maintenance, utilizing capturing and recovery techniques wherever possible.
• Provide comprehensive training to all maintenance personnel on proper handling, recovery, and recycling procedures for refrigerants.
• Maintain a clean, dry system to prolong mechanical seal effectiveness and prevent leaks. Avoid excessive water pressure in the condenser to prevent tube failures. Monitor machinery vibration to prevent damage that could lead to gas leaks.
• Use leak-proof connections for charging and recovery, employing compatible and manufacturer-specified gaskets and mechanical seals. Ensure all refrigerant is recovered before opening the system for maintenance.
• Use geniune Spare parts to avoid any failure of system leading to accidentally release of gas.

Oil-Lubricated Stern Bearing System

The primary method for preventing seawater ingress into an oil-lubricated stern bearing system is a combination of mechanical seals and maintaining a balanced oil pressure. The system uses lip seals to contain the lubricating oil within the stern tube. An oil header tank ensures the oil pressure inside the stern tube is approximately equal to the surrounding seawater pressure. This balanced pressure prevents seawater from entering the stern tube.

Corrective Actions While Afloat

If the stern bearing system fails and seawater begins to ingress, the following temporary corrective actions can be taken while the vessel is still afloat:

• Switch to High-Viscosity Oil: The system can be recharged with a higher-viscosity oil. This thicker oil is less likely to leak past the seals, reducing the rate of seawater ingress.
• Install a Temporary Header Tank: Disconnect the regular oil supply line and connect a 45-gallon drum. This drum, supported by a block and tackle, acts as a temporary header tank with a variable head. The height of the drum can be adjusted by raising or lowering it to match the seawater pressure, ensuring the correct pressure balance is maintained.

Why Two Stern Bearing Oil Header Tanks Are Fitted

In some cases, two stern bearing oil header tanks are fitted, especially on vessels that experience large variations in draft, such as tankers. The two tanks are installed at different heights to accommodate these draft changes.

• The purpose is to match the oil pressure to the changing seawater pressure as the vessel's draft changes.
• By having tanks at different heights, the crew can switch between them to maintain the necessary differential pressure to keep seawater out of the stern tube. The maximum allowable pressure difference between the seawater and the oil is typically 0.3 bar.
• For example, the changeover between the tanks is often done at a specific draft, such as 11.7 meters.

Modern ships often use a single header tank with an air pneumatic system. This system automatically adjusts the oil pressure to match the seawater pressure based on the vessel's draft, eliminating the need for manual checks and tank changes.

A coil-operated brake for winches and deck machinery is designed to automatically adjust the braking force in response to changes in the load on the mooring line. This system ensures the correct force is applied between the brake band and the winch drum at all times.

The core principle is that when an additional load is applied to the mooring line, the line stretches, which in turn loosens the tightening mechanism. This loosening action automatically causes the brake to apply the correct force, maintaining constant tension. This has the significant advantage of being a self-adjusting system, meaning that once it's set, there's no need for a crew member to periodically re-apply the recommended torque. The brake is typically released using a hydraulic lever.

When a vessel is riding at anchor, a mechanism is used to lock the anchor chain and relieve the windlass of the strain. This is crucial for preventing damage to the windlass and ensuring the anchor is securely held.

A Cable stopper, often a pawl of a rod, is engaged with a link of the anchor chain. The pawl acts as a stop, preventing the chain from moving. All the weight and force from the anchor and the vessel's movement are then transferred to this locking device and the ship's structure, effectively relieving the windlass of any strain.

Controllable Pitch Propellers (CPP)

It is preferable to house the main servomotor for a controllable pitch propeller (CPP) in the propeller hub rather than in the shafting forward of the propeller shaft. This design, known as a hub servo system, is preferred over the external servo system, which uses a long push-pull rod extending from the engine room. The primary reason for this preference is that the long push-pull rod in an external servo system is prone to bending. This bending can occur due to the rod's length and the significant water pressure acting against the propeller blades, which can compromise the pitch control mechanism's reliability and precision. Housing the servomotor directly in the hub eliminates the need for this long rod, resulting in a more robust and reliable system.

1. Hydraulic System Maintenance

• Periodic cleaning of hydraulic filters and oil coolers.
• Regular oil sampling (both onboard quick checks and shore analysis) to detect contamination or wear particles.
• Monitoring oil consumption to detect leaks in the system.

2. Mechanical Components

• Greasing all linkages to prevent corrosion and wear.
• Checking and lubricating moving parts as per manufacturer’s recommendations.

3. Operational Checks

• Ensuring familiarization of all relevant personnel with correct operating and maintenance procedures.
• Regular testing of alarms and safety devices.
• In dry dock, verify actual pitch position against remote indicators at the wheelhouse and engine room.
• Test the fail-safe arrangement to ensure it operates correctly in emergencies.

Leakage of treated boiler water (through a leaking blowdown pipe, valve, water tube, or circulating pump) and excessive blowdown both lead to a loss of treated water. Replacing this lost water with untreated makeup water dilutes the TDS and chemical reserves.

Action:

• Inspect all boiler blowdown pipes and valves for leaks and repair as necessary.
• Check for leaks in water tubes (indicated by white smoke from the funnel). Repair any leaks found.
• Inspect circulating pumps for leaks and repair as necessary.
• Once leaks are repaired, add chemicals to restore the desired levels.
• Monitor boiler water conditions through frequent testing.

(ii) Reduction in phosphate reserve, with an increase in chlorides and total dissolved solids:

Seawater ingress is the likely culprit. Seawater contamination introduces carbonates, sulfates, and chlorides of sodium, calcium, and magnesium. These ions react with phosphate in the boiler, forming non-scale sludge, leading to reduced phosphate reserves and increased chlorides and TDS.

Action:

• Identify and plug any leaky condenser tubes causing seawater ingress.
• Inspect and replace sacrificial anodes if necessary. This helps prevent corrosion.
• Increase the frequency and duration of boiler water blowdown.
• If chloride levels remain high, reduce boiler load to 2/3 normal output, blow down to minimum level, and refill with fresh make-up water.
• A complete emptying and flushing of the boiler is the ultimate solution to remove the remaining contamination. Carry out this at the earliest opportunity.

(iii) Reduction in alkalinity reserve only:

• Seawater contamination potentially introduces acidic products that neutralize the alkaline reserve.
• Boiler water leakage (loss of alkaline water).
• Oil contamination (oil can react to reduce alkalinity).
• Ingress of air (air can lead to the formation of acidic products that neutralize alkalinity).

Actions:

• Identify and rectify any seawater ingress.
• Maintain a high hotwell temperature to prevent air ingress.
• Identify and repair any boiler water leaks.
• Identify and eliminate the source of oil contamination.

(iv) Increase in oxygen levels only:

• Poor performance of the de-aerator, allowing oxygen to remain in the feedwater.
• Insufficient hydrazine reserves (hydrazine is an oxygen scavenger).
• Low hotwell temperature (oxygen is more soluble in colder water).
• Leaking feed water pump gland (allowing air to enter).

Actions:

• Inspect and repair any faults in the deaerator.
• Ensure adequate hydrazine reserves are maintained.
• Maintain a high hotwell temperature.
• Identify and repair any gland seal leaks in the feed water pump.

• Complete data allows for the identification of subtle trends indicating developing problems. A gradual decrease in alkalinity, for example, might not immediately exceed the alarm threshold but could signal a developing issue that can be addressed proactively.
• Comparing current results to past results helps establish a baseline and allows for easier detection of anomalies.
• Complete data provides more context during troubleshooting. If a problem arises, having access to a complete history can help identify the root cause more effectively.
• Logged data enables proactive adjustments and repairs before faults escalate, preventing boiler damage and reducing unplanned downtime.

Pump rooms on tankers are required to be mechanically ventilated. The ventilation system must be of the exhaust type and designed to prevent the accumulation of flammable vapors. To ensure this, the system needs to have a minimum capacity of 20 air changes per hour based on the gross volume of the space. The exhaust fans must be a non-sparking type, and the air ducts should be arranged to provide effective ventilation throughout the entire space. The discharge from the exhaust fans must be led to a safe location on the open deck.

Cargo Tank Ventilation

Cargo tanks are ventilated to make them "gas free," which means removing flammable or toxic vapors. This can be achieved using portable fans or blowers. These fans must be constructed to prevent incendiary sparking, for example, if the impeller were to touch the casing. The fans must also have sufficient capacity and penetration to quickly gas-free the entire tank atmosphere.

Alternatively, on tankers equipped with an Inert Gas System (IGS), the system itself can be used for ventilation. To do this, the connection from the scrubber tower is closed, an air inlet from the atmosphere is opened, and the IGS blowers are started. This process effectively ventilates the cargo tanks by drawing in fresh air and pushing out the existing atmosphere.

The primary problem with carrying LNG is maintaining its extremely low temperature of approximately -160°C. Despite the insulated tanks, a small amount of the LNG will inevitably vaporize, a phenomenon known as "boil-off." This boil-off must be managed, as it poses a safety risk and represents a loss of cargo. The process of managing this boil-off is critical and consumes a significant amount of power if the gas is to be reliquefied.

Several methods are used to handle boil-off gas on board LNG carriers:

• Reliquefaction: Heavy-duty compressors are used to compress the boil-off gas, converting it back into a liquid state and returning it to the cargo tanks.
• Mixed Refrigeration: A refrigeration process that uses a mixture of different refrigerants to cool and reliquefy the boil-off gas.
• Expander Cycle: A method that uses an expander to cool the boil-off gas, causing it to reliquefy.
• Using it as Fuel: The boil-off gas can be used as fuel for the ship's engines, either completely or as a partial fuel in a dual-fuel combustion system. This turns a potential problem into a source of power for the vessel.

Oil-Lubricated Stern Bearing System

The primary method for preventing seawater ingress into an oil-lubricated stern bearing system is a combination of mechanical seals and maintaining a balanced oil pressure. The system uses lip seals to contain the lubricating oil within the stern tube. An oil header tank ensures the oil pressure inside the stern tube is approximately equal to the surrounding seawater pressure. This balanced pressure prevents seawater from entering the stern tube.

Corrective Actions While Afloat

If the stern bearing system fails and seawater begins to ingress, the following temporary corrective actions can be taken while the vessel is still afloat:

• Switch to High-Viscosity Oil: The system can be recharged with a higher-viscosity oil. This thicker oil is less likely to leak past the seals, reducing the rate of seawater ingress.
• Install a Temporary Header Tank: Disconnect the regular oil supply line and connect a 45-gallon drum. This drum, supported by a block and tackle, acts as a temporary header tank with a variable head. The height of the drum can be adjusted by raising or lowering it to match the seawater pressure, ensuring the correct pressure balance is maintained.

Why Two Stern Bearing Oil Header Tanks Are Fitted

In some cases, two stern bearing oil header tanks are fitted, especially on vessels that experience large variations in draft, such as tankers. The two tanks are installed at different heights to accommodate these draft changes.

• The purpose is to match the oil pressure to the changing seawater pressure as the vessel's draft changes.
• By having tanks at different heights, the crew can switch between them to maintain the necessary differential pressure to keep seawater out of the stern tube. The maximum allowable pressure difference between the seawater and the oil is typically 0.3 bar.
• For example, the changeover between the tanks is often done at a specific draft, such as 11.7 meters.

Modern ships often use a single header tank with an air pneumatic system. This system automatically adjusts the oil pressure to match the seawater pressure based on the vessel's draft, eliminating the need for manual checks and tank changes.

• R-134a: Suitable for medium and high-temperature applications, serving as a long-term replacement for R-12.
• R-404A: Suitable for low and medium-temperature applications.
• R-407C: A replacement for R-22, suitable for medium and high-temperature applications.
• R-410A: Twice as efficient as R-22 but generally recommended for new systems only.

During Normal Operation:

• Implement a robust monitoring system with daily logs of key parameters to allow for early detection of any anomalies, such as pressure drops or temperature fluctuations, that might indicate a leak.
• Regular Leak Detection: Conduct routine leak tests to identify leaks from joints, seals, gaskets, pipes, and other components.
• Safety Valve Management: Ensure correct setting and operation of safety valves to prevent accidental refrigerant release.

During Maintenance Activities:

• Mandate the complete recovery and recycling of refrigerant gas before any maintenance work commences. Utilize onboard recovery systems, ensuring they are properly maintained and calibrated.
• Implement procedures to minimize refrigerant venting during maintenance, utilizing capturing and recovery techniques wherever possible.
• Provide comprehensive training to all maintenance personnel on proper handling, recovery, and recycling procedures for refrigerants.
• Maintain a clean, dry system to prolong mechanical seal effectiveness and prevent leaks. Avoid excessive water pressure in the condenser to prevent tube failures. Monitor machinery vibration to prevent damage that could lead to gas leaks.
• Use leak-proof connections for charging and recovery, employing compatible and manufacturer-specified gaskets and mechanical seals. Ensure all refrigerant is recovered before opening the system for maintenance.
• Use geniune Spare parts to avoid any failure of system leading to accidentally release of gas.

To increase the ship’s deadweight capacity, one must increase one or more of the following parameters: length, breadth, draught, or block coefficient. Since the question specifically excludes any increase in length, the remaining options must be examined.

• Increasing the breadth or the block coefficient would be structurally complex and generally impractical for an existing vessel.
• Therefore, the most feasible approach is to increase the draught, which can be achieved by reducing the assigned freeboard in accordance with Load Line Regulations.
• As the vessel is a dry cargo ship (Type B), it normally attracts the maximum freeboard. Thus, any opportunity to reduce freeboard could directly increase the allowable draught and, consequently, the deadweight.
• If the ship is currently fitted with wooden hatch covers, replacing them with steel gasketed covers would allow a reduction in freeboard.
• In the original design and construction stage, additional freeboard may have been assigned due to deficiencies in sheer, extent of superstructures, or bow height.
• If any of these deficiencies still exist, appropriate structural modifications—such as adding a superstructure, increasing deck sheer, or adding a forecastle—could permit freeboard reduction. (However, the first two options would be significant engineering undertakings.)
• The vessel may also be deficient in depth. Increasing the ship’s depth—an alteration that has been carried out successfully on some conversions—would raise the freeboard deck. This allows a greater draught for the same assigned freeboard.
• If the ship is of the open shelter-deck type, converting it by providing permanent watertight closures to all openings would effectively raise the freeboard deck, again permitting an increased draught.
• Another possibility is to structurally modify the vessel for classification as a bulk carrier, allowing assignment of Type B-60, which carries a reduced freeboard compared to a standard Type B vessel.
• Although increasing draught by reducing freeboard is the primary viable option, some additional modifications may also contribute.
• For example, sponsons have been added to certain vessels (notably RO-RO ships) to improve stability; the resulting extra buoyancy could be utilised to increase deadweight.
• Similarly, other hull appendages added for non-buoyancy reasons may still provide additional displacement. A common example is the bulbous bow, primarily fitted to reduce wave-making resistance but which also supplies extra buoyancy.

The purpose of the in-water survey is to obtain information on the condition of the hull and machinery of large vessels normally obtained from the Docking Survey. The survey may be carried out instead of any one of the two docking surveys, under the surveillance of a surveyor with the ship at a stable draught in sheltered waters, the in-water visibility is to be good and the underwater hull clean.

The survey requires a self-propelled, steerable survey vehicle fitted with a long-range TV camera to aid steering and check for hull distortion also a close-up high-resolution TV color camera to give a true picture of the state of coatings and for inspection of weld seams. In some cases a 35mm still camera is fitted. An ultrasonic probe is provided to measure plate thicknesses and other equipment includes a depth meter and speed indicator. Power is supplied and information is relayed using an umbilical from the vehicle to the survey boat

The survey boat usually houses a console containing TV monitors. plate thickness printout, audio cassette recorder, video recorder and playback unit, diver communication system, vehicle control system and associated instrumentation.

The survey vehicle is taken to the starting datum by a diver. With the aid of one of the TV monitors and using the shell expansion plan as a map, the vehicle may be guided, from the control console, over the bottom and sides of the hull by following weld runs and by reference to other features such as inlets and tank plugs. Pictures and navigational information are relayed back and video recorded along with plate thicknesses giving the surveyor an integrated visual record of all relevant information. In addition, a plate thickness print-out can be produced and/or an audio recording. The vehicle will also provide pictures of such items as the stern frame, rudder, propeller, bilge keels and hull openings although a diver may be used with a handheld camera for closer inspection of these items and also for inspection of plating on the turn of the bilge. Divers are used to measure stern bearing wear down and pintle clearances, and to inspect such things as stern seals, anodes, pintles and rudder stock couplings.

To facilitate underwater surveys plans must be submitted showing the external features of the hull below the sheer strake together with a key plan indicating the location of these features, also of reference points and the position of water-tight and oil-tight bulkheads. Notes are included on the proposed methods of marking and identifying plates. To assist divers color photographs should be provided of items such as shell openings, rudder closing plates and wear-down gauge plugs.

Provision should be made on the ship identifying bulkheads and frames above the waterline and also for establishing the identity and position of each propeller blade from inside the ship. The design of the ship must facilitate water inspection and repair, for example, sea inlets must be capable of being blanked off and drained to bilges, shell gratings hinged if practicable and anodes easily changed.

Superheater elements, typically U-tubes or serpentine tubes, operate under high temperatures and undergo significant thermal expansion. Their design carefully accommodates this expansion while maintaining secure support:

• Fixed at One End: The tubes are rigidly connected and securely anchored at either the header or the steam distribution manifold.
• Free to Expand at Other End: The opposing end of the tube bank is engineered to move freely. This is achieved through sliding mechanisms within guides or by incorporating expansion loops, which absorb the thermal growth without inducing stress.
• Hanger and Support Bars: The tubes are supported by hanging rods, beams, or alloy bars suspended from the boiler roof or steam drum. These supports are designed with inherent flexibility to accommodate slight movements.
• Serrated or Slotted Tube Support Plates: These specialized plates provide lateral support for the tubes while featuring slots or serrations that permit longitudinal expansion. This design prevents binding and stress on the tubes.
• Flexible Support Grids: Some boiler designs incorporate support grids made from heat-resistant alloys. These grids offer both stability for the tubes and the necessary freedom for them to expand under thermal load.

Boiler carryover refers to the undesirable entrainment of water droplets or impurities within the steam as it exits the steam drum. This phenomenon often results from issues like foaming, priming, or inherent deficiencies in drum design.

The effects of boiler carryover on the superheater and subsequent components are significant:

• Heat Transfer Reduction: Water droplets in the steam lower the temperature of the incoming steam, which directly reduces the superheater's effectiveness. The absorption of latent heat by this moisture prevents the steam from reaching the desired superheat temperature.
• Thermal Stress and Fatigue: The superheater tubes are subjected to fluctuating metal temperatures due to repeated exposure to alternating wet and dry steam. This leads to thermal cycling, which can cause fatigue cracking in the tube material.
• Tube Scaling and Fouling: Impurities present in the carryover (such as salts or silica) deposit on the internal surfaces of the superheater tubes. These deposits act as insulation, leading to localized overheating, further reducing heat transfer efficiency, and creating potential hot spots that can damage the tubes.
• Corrosion and Tube Damage: The presence of moisture and dissolved oxygen within the carryover promotes internal oxidation, pitting, and corrosion under deposit inside the superheater tubes. This significantly increases the risk of tube failure.
• Turbine Blade Damage Risk: Ineffective superheating due to carryover means that wet steam may reach the turbines. This can cause erosion and significant damage to the turbine blades, impacting the overall efficiency and longevity of the turbine.

Procedure for Presenting an Auxiliary Engine for Survey by a Classification Society

When presenting an auxiliary engine for survey by a classification society, the process generally follows one of two methods:

1. Ship staff carry out the job and all reports are made and verified by the Chief Engineer and sent to the classification society for getting credited
2. The auxiliary engine is opened and all parts as required by the surveyor are kept ready for inspection along with the reports

In either case, the following procedure is followed:

• The date of the survey is to be intimated to the surveyor.
• All necessary spare parts must be checked and ordered beforehand.
• Record of all engine running parameters must be maintained and ready for inspection.
• The performance of the engine is taken before opening for a survey and recorded to be presented to the surveyor.
• The record of the last survey report and other necessary reports should be kept ready for inspection.

The engine is opened up as per the procedure and the following items are checked as per the requirement of the surveyor

• The cylinder head - opened, cleaned, valves lapped, fitted back and kept ready for inspection by the surveyor.
• Piston - removed, cleaned, condition checked, piston, ring checked and renewed if necessary. All clearances are measured and recorded.
• Conrod - Cleaned and checked, measurements of ovality and gudgeon pin taken and recorded. Serrations checked for cracks (DP test)
• Cylinder liner - cleaned and inspected, measured and checked and recorded.
• Big end bearing - check for any damage, renewed as per condition.
• Journal bearing and thrust bearing - condition checked and renewed accordingly.
• Crankshaft pin - check condition checked and oil grove checked.
• Check the condition of the camshaft and drive gear
• Overhaul and inspection of turbocharger
• Overhaul the attached pumps as required and suggested by the maker.
• Cleaning and inspection of the air cooler.
• Cleaning and inspection of the scavenge space. Special paint is applied if required.
• Sump cleaning is done.

Following inspection reports are prepared.

• Piston overhaul report.
• Conrod inspection report
• Liner calibration report

• After all inspections, the generator this box back and crankshaft deflection are measured and compared with previous records
• Engine tried out, alarms and trips tested
• Engine performance taken and recorded
• All reports along with photos are prepared and kept on standby.
• Reports include survey report, overall report of the engine, measurement report of the piston, conrod and liner, crankshaft deflection and engine performance report.

Three copies of the report are prepared and duly signed by the classification surveyor

• 1 copy is retained by the surveyor.
• 1 Copy sent to the company.
• 1 Copy placed in the ship survey file

According to SOLAS chapter - 2, part 1, regulation 29.16, every tanker of more than 10,000 GT shall comply with the following:

• The main steering capability due to a single failure in any part of one of the power actuating systems shall be regained in not more than 45 seconds.
• The main steering shall comprise at least two identical power actuating systems, each capable of meeting the requirements. Loss of fluid from one system shall be capable of being detected, and the defective system shall automatically get isolated so that the other system shall remain fully operational

Considering the above regulatory requirements, given below is a “Fail Safe steering gear” suitable for use on a tanker of more than 100,000 T DWT.

Shown in the diagram is a “Fail safe steering gear” having two independent power actuating systems that can

• Work simultaneously in normal operation, meeting the requirement OR
• Work independently and meet the requirement
• In the event of loss of fluid from any one system, it can be detected and isolated automatically so that the other system can remain fully operational.

Working:

• The system incorporates two sets of electric-driven pumps. Both main and auxiliary pumps are on the same shaft. The main pump shown in the diagram is a variable delivery pump
• The variable delivery pump takes suction from the tank and supplies hydraulic oil to the ram cylinders. The oil flow of the pump is determined by the pump actuating lever
• The movement of the pump actuating lever is controlled by the rudder angle order given by the bridge with the help of a bi-directional control valve
• A two-way shock relief valve is fitted between the two cylinders to release the pressure from one side of the cylinder to the other side in case of pressure increase in one of the cylinders due to heavy seas
• By-pass valves are also fitted between two cylinders, which are normally shut during operation. When one system is stopped, there is a pressure drop, as the auxiliary pump has also stopped this opens the by-pass valves, thus removing the hydraulic lock of the ram operation.
• Auto isolation valves in the system are there to isolate one system in case of any failure.

Case 1: Consider an oil leak from any pipe for cylinders 1 and 2 with the No. 1 pump running:

1. No. 1 tank level will come down to L1, and it will sound an alarm on the bridge and in ECR
2. When the tank level further drops to L2, i.e. low-low level, the no. 1 pump stops.
3. Stopping the No. 1 pump also stops the attached auxiliary pump. So the line pressure drops, due to which the normally closed by-pass valves ‘X’ and ‘Y’ open.
4. Simultaneously, the auto isolation valves ‘A’, ‘B’ and ‘C’ will be operated by an electric signal. A, B and C are normally open valves. The electric signal will close them. So, systems 1 and 2 will be completely separated. Thus, the defective system, I.e. system 1, is isolated.
5. Along with the operation of the auto isolation valves, the No. 2 pump will start automatically. The attached auxiliary pump will act on the by-pass valve ‘Y’ and close it. This enables cylinders 3 and 4 to be in normal operation.
6. It should also be noted that since system 1 is completely isolated, there is no oil pressure to operate the bypass valve. So the by-pass valves remain open, thereby removing the hydraulic lock for the ram movement in cylinders 1 and 2

Case 2: Consider an oil leakage from any pipe of cylinders 3 and 4 with the No. 1 pump running:

Points 1, 2 and 3 are the same as case 1

1. Simultaneously, the auto isolation valves ‘A’, ‘B’ and ‘C’ will be operated by an electric signal. This will shut the normally open valves A, B and C. Thus, systems 1 and 2 will be completely separated
2. Along with the operation of auto isolation valves, the No. 2 pump will start automatically. The attached auxiliary pump will act on the by-pass valve ‘Y’ and close. So, cylinders 3 and 4 will come into normal operation.
3. Now, since the leak is between the pipe of cylinders 3 and 4, the level of the no. 2 tank will drop to L1 and give an alarm.
4. The level will further drop to L2, but the pump will not stop and changeover to ensure that the leak is from the pipe of cylinders 3 and 4
5. When the no. 2 tank level drops to L3, the no. 2 pump stops and the no. 1 pump starts to operate the steering using cylinders 1 and 2
6. Starting the no. 1 pump will ensure that the by-pass valve ‘X’ is shut, and stopping the no. 2 pump will ensure that the by-pass valve ‘Y’ is open

This ensures the operation of the steering Gear with the defective system fully isolated.

Maintaining the quality of lubricating oil in main and auxiliary diesel engines is required to prevent engine breakdowns and ensure safe operation. Lubricating oil reduces friction, prevents corrosion, and acts as a cooling medium. Regular testing of the oil is essential to monitor its condition and identify potential problems, such as water contamination or a decrease in viscosity. Onboard testing can provide immediate analysis, while shore-based laboratories offer more detailed analysis, including future life and performance capability. Early detection and correction of issues can prevent costly repairs and downtime.

Methods adopted to maintain the quality of crankcase oil:

(i) Filtration system

The filtration system consists of 3 filters, as shown in the above figure:

• Suction filter with a magnet before the LO pump
• Auto backwash filter after LO cooler
• Bypass filter for auto backwash filter

(ii) Purification system:

• The purification system is shown in the above diagram
• The purifier is run sump to sump to separate water and impurities.
• It helps to maintain the quality of crankcase LO and also avoids the growth of microbes.

(iii) Shipboard LO test:

• LO test is carried out onboard to check the water content, TBN and viscosity of the oil
• This helps to constantly monitor the system and maintain the LO properties

(iv) Laboratory test:

• LO samples are sent for shore analysis to know the detailed condition of LO quality and actions or suggestions given to maintain the quality.

(v) Other methods adopted:

• Visual check of LO sump for discolouration, smell, impurities, etc
• Maintaining proper LO temperature
• Maintaining good LO cooler efficiency
• Keeping the combustion system in a good state.

Plan to Reduce Boiler Uptake Fires:

Preventive Maintenance Schedule

• Carry out regular cleaning, inspection, and adjustment to ensure optimal air-fuel ratio for complete combustion. This minimises the production of soot and unburnt carbon particles.
• Ensure the fuel oil fed to the boiler is properly treated to minimise impurities that contribute to incomplete combustion.
• Conduct frequent inspections to identify and address any issues like burner misalignment, damaged refractory, or excessive soot accumulation before they escalate into a fire.
• Whenever a flame failure occurs, immediately investigate and rectify the root cause to prevent prolonged incomplete combustion. Do not attempt repeated re-ignition until the cause is identified and resolved.

Monitoring and Watch Keeper Instructions:

Watchkeepers will be instructed to continuously monitor the following parameters and report any deviations immediately:

1. Any significant rise indicates potential fire.
2. Visible sparks or flames are clear indications of a fire.
3. Activating high-temperature alarms necessitates immediate investigation.
4. While not a direct indicator of fire, it may be a symptom of blocked flue gas pathways due to soot.
5. Visual monitoring during routine inspections, aided by potentially installed soot accumulation sensors.

• Vanadium combines with sodium and sulphur during combustion process to form eutectic compounds [Penta Sodium Vanadate] which lowers the melting point to about 450°C. These molten compounds are very corrosive and attack the components such as exhaust valves & piston crown.
• A high asphaltene content indicates that fuel may be difficult to ignite and will burn slowly. This will contribute to deposit formation in combustion chamber and exhaust system, especially at low engine loads.

• Consult the engine maker’s manual to identify permissible fuel grades for the specific engine type. This ensures compatibility and compliance with the engine’s design and operational parameters.
• Adhere to specific fuel quality regulations in areas such as Emission Control Areas (ECAs), where low-sulphur fuel may be required. Engine makers may provide specific recommendations for these regions to avoid operational issues.
• Use the ISO 8217-2017 fuel quality standard, which defines limits for key parameters such as sulphur content, viscosity, water, catfines, and ash, ensuring consistent and safe fuel quality.

Ash Content:

• Inorganic impurities like sand, nickel, aluminium, and silicon contribute to abrasive wear and can damage fuel pumps and cylinder liners.

Vanadium:

• Combines with sodium and sulphur, leading to high-temperature corrosion on exhaust valves, turbochargers, and piston crowns.

Catfines (Aluminium and Silicon):

• Abrasive particles in residual fuel oils that can cause severe wear on fuel pumps, valves, and cylinder liners.

Water:

• Leads to cavitation damage in fuel pumps and valves, ignition delays, and potential vapour lock during combustion.

Asphaltenes:

• High levels contribute to sludge formation, leading to deposits in the combustion chamber and exhaust systems, especially under low-load conditions.

Sulphur:

• Excess sulphur forms acids that cause cold corrosion, particularly in areas with low temperatures in the exhaust system.

The oil monitoring system for bilge and tanker ballast discharges ensures that the oil content in discharged water complies with regulatory standards. Below is a description of its general arrangement:

1. Water from the discharge line is sampled before reaching the overboard discharge valve.
2. The sample is directed to the PPM monitor, which measures the oil content in parts per million (PPM).
3. The oil content value from the PPM monitor is sent to a comparator, which compares it to a preset allowable limit.
4. If the oil content is within the allowable limit, the overboard valve opens automatically to discharge the water. If the oil content exceeds the set limit, the overboard valve is shut, and the water is redirected to the slop tank.

The PPM monitor works on the principle of scattered light. Light reflected or scattered by oil particles is measured using a photocell. The intensity of scattered light decreases with increasing oil content. This signal is then analysed and sent to the comparator.

The system records the following data:

• Oil content reading (in ppm)
• Ship's speed
• Oily water discharge rate
• Date and time
• Ship's position

Difficulties encountered with efficient operation:

1. Response Delay in Sampling Pipe: The delay in transporting water samples from the discharge line to the PPM monitor can result in inaccurate or untimely readings.
2. Clogged Sampling Pipe: Accumulation of debris or oil residues can obstruct the sampling pipe, leading to erratic or incorrect readings.
3. Sealing and Cleaning of Optical Windows: The optical components of the PPM monitor, such as the scattered light window, require regular cleaning and maintenance. Dirty or poorly sealed optical windows can cause inaccurate measurements or system malfunction.

Common forms of seal failure in a stern tube

1. Loss of elasticity in seal material – Nitrile rubber seals may lose their elastic properties over time, reducing their sealing effectiveness.
2. Surface damage to chrome liner – Grooving or scoring of the chrome liner can impair sealing surfaces, leading to leakage.
3. Excessive shaft vibration – Heavy vibration of the propeller shaft can cause uneven wear and seal deformation.
4. Insufficient cooling – Inadequate cooling can cause rubber sealing elements to harden and eventually fail.
5. Exceeding running hour limits – Operating beyond the manufacturer’s recommended service life increases the risk of seal failure.
6. Deterioration of oil quality – Contaminated or degraded oil reduces lubrication and protection, accelerating seal wear.
7. Incorrect header tank level adjustment – Failure to adjust the header tank according to vessel draft can cause oil loss, leading to inadequate lubrication and seal damage.

Restricting oil loss due to seal failure whilst on passage

1. Use of high-viscosity oil – Recharge the system with a thicker oil to reduce leakage rate through damaged seals.
2. Temporary oil supply arrangement –
   • Disconnect the existing oil supply line.
   • Connect a 45-gallon drum supported by a block and tackle arrangement.
   • Adjust the drum height to vary the oil head pressure, matching it to the surrounding water pressure and minimizing leakage.
3. Fresh water introduction – Supply fresh water to the gravity tank to emulsify with any leaked oil. The resulting emulsion helps coagulate around the damaged seal area while the oil is circulated to maintain lubrication and sealing.

Materials for Sealing Rings and Propeller Shaft Liner:

• Sealing Rings: Nitrile rubber (NBR) is a commonly used material for stern tube sealing rings due to its good oil resistance, elasticity, and relatively low cost.
• Shaft Liner: Chrome-plated steel is a common material for stern tube liners. The chrome plating provides a hard, smooth, and corrosion-resistant surface, minimizing wear and improving the life of the sealing rings.

(a) Explaining Creep, Brinelling, Fretting, and Fretting Corrosion:

Creep:

• Creep is the time-dependent permanent deformation of a material under sustained stress at elevated temperatures. It occurs at stresses significantly below the material's yield strength. The rate of creep depends on material properties, temperature, time under load, and the applied stress. Creep progresses in three stages: primary (decreasing rate), secondary (constant rate), and tertiary (rapidly increasing rate leading to failure). An example is the creep of a turbine blade, causing it to contact the casing and fail.

Brinelling:

• Brinelling is the formation of permanent indentations on a hard surface due to heavy or repeated impact loads over a small area. This can occur during standstill or rotation and is often caused by improper installation (e.g., of bearings). Even small indentations can lead to malfunctions like chattering or vibration, accelerating other wear mechanisms. The hardness of materials needs to be considered during design to prevent brinelling.

Fretting:

• Fretting is surface wear between two contacting surfaces under load and small-amplitude cyclic motion (vibrational wear). It's common in bolted or keyed joints where relative movement is unintended. Fretting initiates fatigue cracks, leading to fatigue failure. The severity depends on factors like displacement amplitude, load, material properties, number of cycles, and lubrication. Lubricant is often squeezed out from between the surfaces during the cyclic movement, resulting in direct metal-to-metal contact.

Fretting Corrosion:

• Fretting corrosion is a specific type of fretting wear that involves chemical reactions between the contacting surfaces. The repeated rubbing and microscopic movement leads to the formation of oxides and other corrosion products, exacerbating the wear and leading to more severe damage than fretting alone. This process is typically accelerated in the presence of moisture or other corrosive environments.

(i) A-Frame

Cause of Cracking:

• Stress concentration due to sharp changes in section.
• Incorrect preparation of plate edges.
• Welding root faults, like lack of penetration.
• Engine overload or excessive crosshead force.
• Vibrations and twisting.
• Loose tie bolts or termination of horizontal stringers.

Avoidance Measures:

• Use a monoblock structure for the A-frame to provide structural rigidity.
• Avoid sharp changes in section to reduce stress concentration.
• Address manufacturing defects with proper treatment.
• Make the guides integral with the A-frame or manufacture separately from cast iron. Perform regular inspections and checks on tie bolt tightness. Ensure engine operates within specified load, temperature, and pressure limits.

Rectification of Cracks:

• Conduct visual inspections and non-destructive testing (Dye-Penetration Test, Magnetic Particle Test) to locate cracks.
• If necessary, drill and tap the crack to prevent its spread.
• With shore assistance and class approval, remove the crack and repair it with metal welding, using similar or superior material.
• Pre- and post-heat treatments may be required for proper metal integration.

(ii) Bedplate Longitudinal Girder

Cause of Cracking:

• Manufacturing defects such as welding faults.
• Imbalanced engine loads.
• Incorrect tension of fastenings, like holding-down bolts and tie bolts.
• Excessive vibration, which may be due to improper operation of vibration dampers.

Avoidance Measures:

• Ensure constructional strength to provide sufficient rigidity for various forces.
• Prevent sharp changes in section, which can increase stress concentration.
• Eliminate manufacturing defects with proper heat treatments and welding techniques.
• Operate the engine within specified load, temperature, and pressure limits.
• Regularly inspect and maintain all fastenings.

Rectification of Cracks:

• Perform visual and non-destructive testing to locate and assess the extent of the crack.
• Drill and tap the crack if needed to control propagation.
• If shore assistance is available, perform grinding and welding repair under class approval, followed by pre- and post-heat treatments to maintain material integrity.

(iii) Bedplate Transverse Girder

Cause of Cracking:

• Cylinder overload, often from excessive power output, causing high stress.
• Misalignment of the crankshaft, which can lead to uneven loading.
• Material defects and high residual stresses in welded areas.
• Deformation of the tank top due to pressurization or overheating.

Avoidance Measures:

• Build the bedplate with M.S. plates and cast steel cross girders, assembled and welded for longitudinal and transverse strength.
• Reinforce longitudinal strength by constructing bedplate sides as box girders.
• Use cast steel cross girders under the main bearing for transverse strength.
• Place resin cast chocks between the bedplate and tank top to absorb shocks and stresses.

Maintenance and Rectification:

• Perform monthly checks on bolt tension and engine load.
• Regularly measure and maintain crankshaft alignment.
• Check and adjust main bearing jack bolt tension.
• In cases of cracks, follow inspection and repair protocols similar to those for the A-frame and longitudinal girders, including pre- and post-heat treatments where necessary.

Boiler Water Level Controller – Float Operated Type

A simple float-operated water level controller consists of:

• A float chamber connected to the boiler steam drum by two lines — one for steam and one for water.
• A float inside the chamber, which rises and falls with changes in water level.
• A mechanical linkage or rod attached to the float, which extends to an electric sensor unit mounted above the chamber.

Working Principle:

• As the float moves up or down, it shifts a contactor along a variable resistance track or magnetic switches.
• This movement changes the electrical output signal, which is sent to a square-root converter.
• The converter transforms the electrical signal into a proportional pneumatic signal.
• The pneumatic signal acts on the diaphragm of the feed water control valve actuator, modulating feed flow to maintain the set water level.

Reasons for Using a Float-Operated Type

1. Reliability: Unlike constant/variable head leg systems, there is no need to maintain a filled reference column.
2. Simplified Installation: Electrical sensing eliminates the need for long impulse tubes for remote indication.
3. Ease of Maintenance: The electric sensor unit can be easily replaced without dismantling the float chamber.
4. Lower Cost: Fewer mechanical parts and no head leg piping reduce installation and maintenance expenses.

Explanation of Terms (Analogy with Controller and Boiler)

: In this system, the float is the detecting element. It directly senses the water level, which is the controlled variable, and its movement provides a signal that represents the current state of the system.

: The square root converter and the feedwater controller collectively act as the servo motor. They are the mechanisms that receive the signal from the detecting element and perform the physical action (opening or closing the feedwater valve) to correct the water level.

: The set point is the desired value. This is a fixed input to the square root converter (or a comparator) that represents the ideal water level that the system aims to maintain. The controller continuously works to match the actual water level to this desired value.

Corrosion is a natural process that degrades materials, especially metals, through a chemical or electrochemical reaction with their environment. Understanding its causes and implementing effective prevention strategies are critical in maritime operations to ensure the safety and longevity of a ship's components. Here's a detailed breakdown of the causes of corrosion and how it can be limited for specific shipboard equipment.

(a) Internal and External Surfaces of Auxiliary Steam Lines

Causes of Corrosion

• Internal Surfaces: Corrosion on the inside of steam lines is primarily caused by dissolved oxygen and other gases present in the boiler feedwater and steam. When exposed to the atmosphere, the water in feed and cascade tanks absorbs oxygen, which then becomes highly corrosive at high temperatures. Additionally, internal surfaces can suffer from impingement corrosion caused by a combination of erosion, cavitation, and water hammering.
• External Surfaces: The external corrosion of steam lines is typically due to a lack of protective coating. Exposed metal surfaces are vulnerable to the moist, humid air found in the marine environment, leading to rust formation.

Limiting Corrosion

• Manufacturer's Role: Manufacturers must design systems that allow for proper deaeration of boiler feedwater to remove dissolved gases. They should also specify high-quality materials resistant to erosion and cavitation.
• Ship's Personnel's Role: Ship's crew must implement proper boiler water treatment to control oxygen levels. Maintaining the cascade tank temperature at approximately 85°C helps release dissolved air. It's also crucial to keep feed and cascade tank doors closed to prevent air from entering. For external surfaces, regular painting and re-coating of the pipelines with appropriate heat-resistant paints is essential to provide a protective barrier against the environment.

(b) External Surfaces of Auxiliary Boilers

Causes of Corrosion

• The main cause of external boiler corrosion is exposure to moist and humid environmental conditions. This is often exacerbated by a damaged or deteriorated protective coating. Improper paint selection or application, which can cause the paint to peel, leaves the underlying metal vulnerable to oxidation.

Limiting Corrosion

• Manufacturer's Role: Manufacturers must apply a durable, high-thermal-resistance paint or coating to the boiler's exterior surfaces. This coating must be able to withstand the high operating temperatures without cracking or flaking.
• Ship's Personnel's Role: Ship's crew are responsible for the upkeep and maintenance of this protective coating. This involves ensuring a proper painting job is done, leaving no surfaces unprotected, and periodically inspecting and re-coating the surfaces to maintain the integrity of the barrier.

(c) Water Boxes of Seawater Coolers and Condensers

Causes of Corrosion

• Corrosion in these components is often due to galvanic corrosion, also known as differential preferential corrosion. This occurs because the materials of the water boxes and their covers are different from the tubes within the coolers and condensers. The tubes, which have higher corrosion resistance, act as a cathode, while the water boxes, being less noble, act as an anode and corrode preferentially, especially in the presence of seawater, which acts as an electrolyte.
• Improper surface protection with paints or coatings can also accelerate this process.

Limiting Corrosion

• Manufacturer's Role: Manufacturers design these systems with provisions for sacrificial anodes, typically made of zinc, to be installed in the water boxes.
• Ship's Personnel's Role: The ship's crew must regularly inspect and replace these zinc anodes as they are consumed. The anodes corrode preferentially, protecting the more critical water box and tube materials. Additionally, proper surface preparation and painting with high-quality marine coatings are necessary to provide an extra layer of protection.

(d) Main Seawater Inlet Pipes

Causes of Corrosion

• Like water boxes, these pipes are susceptible to galvanic corrosion because they are connected to the ship's steel hull, which acts as a large cathode, causing the pipes (if made of a less noble metal) to corrode preferentially.
• The internal rubber or epoxy coating that protects the pipes from seawater can get damaged, exposing the metal underneath to corrosive action.
• Insufficient or damaged external paint protection also contributes to corrosion from the marine environment.

Limiting Corrosion

• Manufacturer's Role: Manufacturers should ensure that the pipes are properly coated with an internal epoxy or rubber lining and an external marine-grade paint. The design must also consider the potential for galvanic corrosion by either selecting appropriate materials or providing a protective system.
• Ship's Personnel's Role: The crew must perform periodic checks of the internal coating and renew it whenever damage is found. They are also responsible for maintaining the external paintwork to prevent corrosion from the outside.

Creep is the slow, time-dependent deformation of a material when it is subjected to a constant stress, particularly at high temperature. Over time, the material slowly elongates or deforms permanently under the applied load, even if the stress is below the material's yield strength.

Action:

• Creep occurs because the material's atomic structure gradually shifts under stress, especially at elevated temperatures where atomic movement is more pronounced.
• There are three stages of creep:
  1. Primary creep: A rapid initial deformation that slows down over time.
  2. Secondary creep: A steady rate of deformation.
  3. Tertiary creep: Accelerated deformation leading to failure.

Factors Influencing Creep:

• Temperature: Higher temperatures increase atomic mobility, accelerating creep.
• Stress: Higher applied stress results in faster creep.
• Material Composition: Materials with a more tightly bonded atomic structure (like metals with higher melting points) exhibit slower creep.

(ii) Brinelling:

Brinelling refers to the permanent indentation or damage that occurs on a hard surface when it is subjected to excessive localized pressure, usually by a hard, stationary object pressing against it. This often occurs in bearings or mechanical contacts.

Action:

• When a hard object (such as a ball bearing) exerts excessive pressure on a softer material, it creates indentations or marks (brinells) on the surface. These indentations may lead to increased friction and wear over time.
• Brinelling typically occurs when the bearing or contact surface is subjected to a static or repeated load beyond its design limits, often during high-pressure contact.

(iii) Fretting:

Fretting is the wear and degradation that occurs at the interface of two materials under small oscillatory movements or vibrations. These movements cause repeated micro-sliding or rubbing, leading to material removal and surface damage.

Action:

• Small relative movements between contacting surfaces cause localized wear, leading to the formation of debris and wear particles. The areas in contact experience high friction and wear, resulting in surface degradation. Over time, this can lead to fatigue and cracking in the material.
• Fretting is most common in situations where there is a slight movement between two components under load, such as in bearing races or gear interfaces.

(iv) Fretting Corrosion:

Fretting corrosion is the combination of mechanical wear and electrochemical corrosion at the interface of two materials, where small oscillatory movements occur. The wear process exposes fresh surfaces to air or water, and the material at the contact point becomes prone to corrosion due to the creation of micro-galvanic cells.

Action:

• The fretting motion removes protective oxide films on the surfaces, exposing fresh metal, which reacts with moisture or oxygen to form corrosion products.
• This results in localized corrosion at the fretting contact areas, which accelerates wear and degradation. The corrosion can be particularly damaging if the environment is corrosive, such as in marine or industrial applications.

• The rotor is fitted to the tapered rudder stock. The rudder stock carries the weight of the rudder, supported by a rudder carrier bearing.
• The stator is fixed to the ship’s structure, forming a rigid support.
• The fixed vanes are evenly spaced inside the stator bore, while the rotating vanes are equally spaced on the rotor.
• These vanes form two sets of pressure chambers in the annular space between the rotor and stator. Hydraulic fluid is supplied at pressure to one set of chambers, causing the rotor and rudder to rotate in the required direction based on the steering order from the wheelhouse.
• The weight of the rudder and rudder stock is carried by the rudder carrier bearing, which is mounted on steel chocks supported by thicker deck plating to ensure stability and handle the load.
• There is a vertical clearance between the stator flange and the anchor bracket to allow for rudder "jump" (vertical movement).
• Another clearance exists between the top of the anchor bracket and the stator flange to accommodate for rudder wear down or rudder drop over time. The total clearance provided is around 38 mm, allowing the system to absorb wear and vertical movement without affecting performance.

• The fixed and rotary vanes are made from modular cast iron and are secured to the rotor and stator using high-tensile steel dowel pins and cap screws to maintain strength and prevent detachment under stress. A key is fitted along the length of the rotary vanes to provide additional reinforcement and ensure the strength of the rotor.
• The sealing of the vanes is achieved using sealing strips made of cast iron. These strips are fitted into grooves along the edges of the vanes. The sealing strips are backed by elastically loaded synthetic rubber, which provides a tight seal by pressing against the faces of both the fixed and rotating vanes. This arrangement prevents hydraulic fluid leakage.

1. Hydraulic Locking: This involves closing the manual isolating valves provided for each cylinder (in ram-type systems) or each vane chamber (in vane-type systems). This prevents hydraulic fluid flow, thus immobilizing the rudder.
2. Mechanical Locking: Three methods are available:

• A spanner is fitted to the rudder stock head nut and secured to the ship's structure, directly preventing rudder movement.
• If provided, tow gigs are fitted between the crosshead and cylinder base, mechanically locking the steering mechanism
• (Assuming a braking system is integrated into the design) Engaging the brake will prevent any movement of the rudder.

Fatigue is progressive and localised structural damage caused by cyclic loading, where the maximum stress is below the ultimate tensile strength. The relationship between stress level, cyclic frequency, and operating life depends on whether the fatigue is high-cycle/low-stress or low-cycle/high-stress.

High-cycle fatigue (low stress-high cycle):

• This occurs at lower stress levels over a high number of cycles, resulting in elastic deformation. The component can withstand more cycles at these lower stress levels, and its life expectancy is determined by the S-N curve, which predicts the number of cycles before failure at a given stress level. For example, fatigue in turbocharger blowers often results from prolonged vibration over numerous cycles.

Low-cycle fatigue (high stress-low cycle):

• This occurs at high-stress levels over fewer cycles, causing plastic deformation in the material. This type of fatigue is typically assessed by a strain curve. If the stress level increases, the component's operating life decreases, as higher stress accelerates the onset of failure. For example, air receivers filling automatically face high stress and experience fewer cycles before failure.

If stress levels or the number of cycles increase beyond the material’s capacity, failure will occur sooner. It is important to keep stress levels within allowable limits for extended component life.

• Surface roughness, porosity, inclusions, and abrupt section changes all create stress concentrations, lowering fatigue strength.
• Coarse grain size, specific chemical compositions, and cold working introduce residual stresses that reduce fatigue resistance.
• Corrosion, erosion, and decarbonisation weaken the material and accelerate fatigue crack initiation and propagation.
• Faulty workmanship during assembly or processing introduces defects that may significantly shorten the component's life.

• Cylinder overload due to excess power puts excessive stress on the girders.
• Incorrect crankshaft alignment induces uneven loading and stress concentrations.
• Material defects, high residual stresses in welds, heat-affected zone hardening, and the presence of dissolved oxygen all reduce fatigue resistance.
• Tank top deformation from pressurisation or overheating adds stress to the bedplate.

To minimise the risk of fatigue cracking:

(i) Constructional strength:

• Bed plates are made up of M.S. plates with four steel casting, which are assembled and welded together so that the bed plate is strong longitudinally & transversely with good resistance to twisting along its length.
• Longitudinal strength is obtained by fabricating each side of the bed plate in the form of a box girder.
• The cast steel cross girder in which the main bearing is placed contributes to the bed plate's transverse strength and resistance against twisting along its length.
• Resin cast chocks are used between the bedplate and the double bottom tank top to absorb the shocks & stress.

(ii) Maintenance:

• Monthly checks on the bolt tension.
• Monthly checks on engine load using power cards & measuring cylinder peak pressure.
• Regular checking of tension for main bearing jack bolts as recommended by engine manufacturers.
• Regular checks on crankshaft alignment by taking deflection & compare with recommended value.
• By maintaining engine operations at specified load, temperature, pressure, speed, etc.

(a) Advantages of Using Steam Turbine Propulsion for LNG Carriers

Steam turbine propulsion offers the following advantages for vessels carrying LNG cargo:

1. Utilisation of boil-off gas (BOG): LNG naturally evaporates during the voyage, producing boil-off gas. This gas can be used directly as boiler fuel, helping to control cargo tank pressure and avoiding wastage of the gas.
2. No need for a boil-off gas re-liquefaction plant: Since the natural boil-off gas can be consumed in the boilers, there is no need for energy-intensive and complex re-compression or re-liquefaction arrangements.
3. Fuel flexibility: Steam boilers can operate on natural gas, heavy fuel oil (HFO), marine gas oil (MGO), or a combination of these fuels, providing good operational flexibility.
4. Increased cargo space / reduced fuel storage requirement: As boil-off gas from the cargo can be used as fuel, the vessel does not need to carry excessive quantities of conventional fuel oil, allowing more space to be available for cargo.
5. High reliability and low maintenance: Steam turbines have fewer moving and no heavy reciprocating parts. This results in less wear and tear, reduced frictional losses, lower lubricating oil consumption, and less frequent maintenance.
6. Smooth and quiet operation: Steam turbines provide continuous rotary motion, resulting in low noise and vibration, reduced hull vibration and fatigue, and improved crew comfort.
7. Cleaner combustion: LNG burns relatively cleanly, producing very low sulphur emissions and fewer deposits compared with conventional heavy fuel oil.
8. Simple gas combustion arrangement: Unlike internal-combustion gas engines, steam boilers do not require precise high-pressure gas admission timing and are not affected by problems such as engine knocking.
9. Lower gas pressure: Gas can be supplied to the boilers at relatively low pressure, reducing the hazards associated with high-pressure gas fuel systems.
10. Good redundancy: LNG steam plants are commonly arranged with more than one boiler. If one boiler is shut down for maintenance or becomes unavailable, the vessel can continue operating with the remaining boiler(s).

(b)(i) Safety Precautions for Gas Pipeline Supplying the Boiler and Burning Gas in the Boiler

• Gas pipelines must not pass through accommodation spaces, service spaces, or control stations, unless fully compliant with regulations.
• Fuel piping to be designed to comply with SB – 1/6 of steel vessel rules.
• Maximum pressure in the fuel gas supply line to not exceed 10 bar.
• All pipelines to be welded; flanged connections only permitted at equipment connections.
• Gas-tight compartments containing fuel piping should have direct access to the open deck.
  • If not possible, access via gas-safe spaces must be through self-closing gas-tight doors.
• Compartments to be fitted with mechanical exhaust ventilation.
• Gas detection systems to be fitted in the compartment and boiler room.
• Incorporate block and bleed valve arrangement in pipelines to comply with purging requirements.
• Entire pipeline supplying methane gas to machinery spaces to be double-walled (annular type) and purged with nitrogen before and after gas-burning operations.
• Nitrogen gas pressure in annular space to be maintained; leakage alarms to be activated if methane detected.
• Boiler room fitted with methane gas sensors with alarm and venting arrangements.
• Boiler room to be continuously ventilated with methane monitoring in air.
• Boiler room separated from machinery space by air-lock antechamber with self-closing doors.

(b)(ii) Means of Getting Rid of Excess Gases During Loading or Discharge

• Cooldown process is carried out to prevent excessive boil-off during loading/discharge.
• Cooldown achieved by supplying liquid methane to spray headers via a distribution grid, directed to various tank levels as required.
• Boil-off vapour is passed through a high-duty compressor back to shore via the vapour return line.
• When liquid is detected at the tank bottom, cooldown is considered complete.
• Primary insulation and secondary barrier temperatures maintained between –80°C to –100°C.
• Tank pressure is controlled using compressors and by varying liquid flow to spray headers.
• Before starting loading, the shore flow for cooldown is gradually reduced.
• After cooldown, loading starts slowly and increases gradually to full rate.
• Tank pressures are monitored; maximum loading rate is governed by compressor capacity to return vapour to shore.

1. If Bumping Clearance is Too Small:

• The piston may physically strike the cylinder cover, leading to mechanical damage, including deformation of the piston, cylinder head, or connecting rod.
• Frequent breakdowns and repairs may occur due to damage caused by insufficient clearance.
• Piston collisions can result in overheating or failures, posing safety risks.

2. If Bumping Clearance is Too Large:

• Larger clearance volumes increase the amount of high-pressure air trapped at the end of the compression stroke. This trapped air expands during the suction phase, reducing the effective stroke for fresh air intake.
• To achieve the required compression pressure, the compressor must run for a longer time, consuming more energy and reducing operational efficiency.
• The increased clearance volume causes a drop in compressor performance, as shown in the graph of volumetric efficiency vs. clearance volume.

• These valves open and close rapidly, aligning with the compressor's suction, compression, and discharge strokes, ensuring minimal time lag for efficient operation.
• The spring mechanism ensures the valves close securely during the compression and discharge strokes, preventing reverse air flow and maintaining efficiency.
• The plates are light in weight, reducing inertia. This allows for quicker valve movement and better responsiveness.
• The lightweight nature of the plates ensures a higher lift, allowing more air to pass through during operation, reducing resistance and improving flow efficiency.
• The design of spring-loaded plate valves ensures that there is minimal pressure drop across the valve, enhancing overall performance.
• These valves are designed to avoid hammering against the valve seat during closure, minimizing wear and tear and reducing operational noise.

In multistage reciprocating compressors, cylinders are of different sizes, so stages appear unequal.

Why:

• As air is compressed in the first stage, its pressure increases and volume decreases.
• Therefore, the next stage handles a smaller volume of air.
• Hence LP cylinder is larger and HP cylinder is smaller.
• This gives balanced compression work and allows each stage to compress within safe temperature and pressure limits.

Conclusion:

Stages appear unequal because each higher stage compresses smaller volume, higher pressure air.

Why inter-cooling is used:

• Air temperature rises during first-stage compression.
• Hot air has larger specific volume, so more work is needed in the next stage.
• Inter-cooling removes heat and reduces air temperature before entering the next stage.
• This reduces compression work, improves efficiency, lowers discharge temperature, and protects valves/lubrication.

Additional benefit:

• It also helps condense moisture and oil vapour, which can then be drained off.

Conclusion:

Inter-cooling improves efficiency, reduces power consumption, and increases compressor safety.

1. Engine Performance Check – Record main engine performance parameters and ensure there is no power imbalance between units.
2. Crankshaft Deflection – Measure crankshaft deflections and compare results with sea trial values to detect any misalignment or deformation.
3. Bearing Clearances – Measure and verify correct clearances for all units’ main bearings, crankpin bearings, crosshead bearings, and thrust bearing.
4. Foundation & Tie Rods – Check all engine foundation bolts and tie rods for correct tightening as per maker’s specifications; ensure none are slack.
5. Top Bracing Arrangement – Inspect the engine top bracing to ensure it is in good condition and correctly adjusted.
6. Propeller & Hull Condition – Arrange for an underwater survey to check the propeller and hull for:
   • Damage to propeller blades (indentation, cracks, or blade loss)
   • Deformation or fouling on hull near aft end
7. Tail Shaft Coupling Bolts – Inspect tail end shaft coupling bolts for any slackness or wear.
8. Vibration Source Correlation – Check for possible resonance where propeller-induced vibration and hull-induced vibration coincide, e.g., M/E units at TDC position while a propeller blade enters the wake.
9. Propeller Position & Balance – Verify correct positioning of the propeller and ensure it is dynamically balanced.
10. Tip Clearance – Ensure propeller tip-to-hull clearance is as per design and not reduced due to propeller shift or structural deformation.
11. Tunnel Shaft Bearings – Check tunnel shaft bearings for any damage or excessive wear.
12. Ballast Condition Effect – If in ballast condition, confirm that the propeller remains fully immersed; partial immersion can cause vibration.

1. Trim Adjustment – Trim the vessel by filling the aft peak tank to fully immerse the propeller and reduce cavitation.
2. Barred Range Avoidance – Avoid running the main engine continuously in its barred range to prevent resonance build-up.
3. Foundation & Tie Rod Tightening – Tighten any loose foundation bolts or tie rods to the correct maker’s specified torque.
4. Coupling Bolt Tightening – Secure any loose tail end shaft coupling bolts.
5. Bearing Clearance Correction – Replace or adjust bearings to restore correct clearances if found incorrect.
6. Power Imbalance Correction – Overhaul or adjust units to eliminate any detected power imbalance.
7. Propeller/Hull Repairs – If propeller or hull damage is detected (e.g., blade cracks, deformation, shearing), arrange dry docking for repair or replacement.

• Keyless design avoids stress concentration caused by keys and keyways.
• Stresses are evenly distributed across the internal surface of the propeller boss
• The absence of a keyway increases the friction available for torque transmission.
• The design prevents overstressing or permanent damage to the propeller hub during operation.
• The keyless arrangement simplifies the propeller and shaft interface, making it easier to manufacture and maintain.

• With a coefficient of friction of 0.28, it minimizes the likelihood of propeller slippage.
• Its expansion rates are similar to those of steel, reducing the risk of misalignment or loosening during temperature variations.
• Pearlitic cast iron exhibits excellent resistance to fretting, which is important for prolonged and reliable operation.

• High-strength epoxy Araldite filling is used to bond the sleeve to the propeller securely.
• The bonding material is applied with a thickness of approximately 1 mm, ensuring adequate adhesion and durability.

Boiler Water Level Controller – Float Operated Type

A simple float-operated water level controller consists of:

• A float chamber connected to the boiler steam drum by two lines — one for steam and one for water.
• A float inside the chamber, which rises and falls with changes in water level.
• A mechanical linkage or rod attached to the float, which extends to an electric sensor unit mounted above the chamber.

Working Principle:

• As the float moves up or down, it shifts a contactor along a variable resistance track or magnetic switches.
• This movement changes the electrical output signal, which is sent to a square-root converter.
• The converter transforms the electrical signal into a proportional pneumatic signal.
• The pneumatic signal acts on the diaphragm of the feed water control valve actuator, modulating feed flow to maintain the set water level.

Reasons for Using a Float-Operated Type

1. Reliability: Unlike constant/variable head leg systems, there is no need to maintain a filled reference column.
2. Simplified Installation: Electrical sensing eliminates the need for long impulse tubes for remote indication.
3. Ease of Maintenance: The electric sensor unit can be easily replaced without dismantling the float chamber.
4. Lower Cost: Fewer mechanical parts and no head leg piping reduce installation and maintenance expenses.

Explanation of Terms (Analogy with Controller and Boiler)

: In this system, the float is the detecting element. It directly senses the water level, which is the controlled variable, and its movement provides a signal that represents the current state of the system.

: The square root converter and the feedwater controller collectively act as the servo motor. They are the mechanisms that receive the signal from the detecting element and perform the physical action (opening or closing the feedwater valve) to correct the water level.

: The set point is the desired value. This is a fixed input to the square root converter (or a comparator) that represents the ideal water level that the system aims to maintain. The controller continuously works to match the actual water level to this desired value.

Corrosion is a natural process that degrades materials, especially metals, through a chemical or electrochemical reaction with their environment. Understanding its causes and implementing effective prevention strategies are critical in maritime operations to ensure the safety and longevity of a ship's components. Here's a detailed breakdown of the causes of corrosion and how it can be limited for specific shipboard equipment.

(a) Internal and External Surfaces of Auxiliary Steam Lines

Causes of Corrosion

• Internal Surfaces: Corrosion on the inside of steam lines is primarily caused by dissolved oxygen and other gases present in the boiler feedwater and steam. When exposed to the atmosphere, the water in feed and cascade tanks absorbs oxygen, which then becomes highly corrosive at high temperatures. Additionally, internal surfaces can suffer from impingement corrosion caused by a combination of erosion, cavitation, and water hammering.
• External Surfaces: The external corrosion of steam lines is typically due to a lack of protective coating. Exposed metal surfaces are vulnerable to the moist, humid air found in the marine environment, leading to rust formation.

Limiting Corrosion

• Manufacturer's Role: Manufacturers must design systems that allow for proper deaeration of boiler feedwater to remove dissolved gases. They should also specify high-quality materials resistant to erosion and cavitation.
• Ship's Personnel's Role: Ship's crew must implement proper boiler water treatment to control oxygen levels. Maintaining the cascade tank temperature at approximately 85°C helps release dissolved air. It's also crucial to keep feed and cascade tank doors closed to prevent air from entering. For external surfaces, regular painting and re-coating of the pipelines with appropriate heat-resistant paints is essential to provide a protective barrier against the environment.

(b) External Surfaces of Auxiliary Boilers

Causes of Corrosion

• The main cause of external boiler corrosion is exposure to moist and humid environmental conditions. This is often exacerbated by a damaged or deteriorated protective coating. Improper paint selection or application, which can cause the paint to peel, leaves the underlying metal vulnerable to oxidation.

Limiting Corrosion

• Manufacturer's Role: Manufacturers must apply a durable, high-thermal-resistance paint or coating to the boiler's exterior surfaces. This coating must be able to withstand the high operating temperatures without cracking or flaking.
• Ship's Personnel's Role: Ship's crew are responsible for the upkeep and maintenance of this protective coating. This involves ensuring a proper painting job is done, leaving no surfaces unprotected, and periodically inspecting and re-coating the surfaces to maintain the integrity of the barrier.

(c) Water Boxes of Seawater Coolers and Condensers

Causes of Corrosion

• Corrosion in these components is often due to galvanic corrosion, also known as differential preferential corrosion. This occurs because the materials of the water boxes and their covers are different from the tubes within the coolers and condensers. The tubes, which have higher corrosion resistance, act as a cathode, while the water boxes, being less noble, act as an anode and corrode preferentially, especially in the presence of seawater, which acts as an electrolyte.
• Improper surface protection with paints or coatings can also accelerate this process.

Limiting Corrosion

• Manufacturer's Role: Manufacturers design these systems with provisions for sacrificial anodes, typically made of zinc, to be installed in the water boxes.
• Ship's Personnel's Role: The ship's crew must regularly inspect and replace these zinc anodes as they are consumed. The anodes corrode preferentially, protecting the more critical water box and tube materials. Additionally, proper surface preparation and painting with high-quality marine coatings are necessary to provide an extra layer of protection.

(d) Main Seawater Inlet Pipes

Causes of Corrosion

• Like water boxes, these pipes are susceptible to galvanic corrosion because they are connected to the ship's steel hull, which acts as a large cathode, causing the pipes (if made of a less noble metal) to corrode preferentially.
• The internal rubber or epoxy coating that protects the pipes from seawater can get damaged, exposing the metal underneath to corrosive action.
• Insufficient or damaged external paint protection also contributes to corrosion from the marine environment.

Limiting Corrosion

• Manufacturer's Role: Manufacturers should ensure that the pipes are properly coated with an internal epoxy or rubber lining and an external marine-grade paint. The design must also consider the potential for galvanic corrosion by either selecting appropriate materials or providing a protective system.
• Ship's Personnel's Role: The crew must perform periodic checks of the internal coating and renew it whenever damage is found. They are also responsible for maintaining the external paintwork to prevent corrosion from the outside.

Creep is the slow, time-dependent deformation of a material when it is subjected to a constant stress, particularly at high temperature. Over time, the material slowly elongates or deforms permanently under the applied load, even if the stress is below the material's yield strength.

Action:

• Creep occurs because the material's atomic structure gradually shifts under stress, especially at elevated temperatures where atomic movement is more pronounced.
• There are three stages of creep:
  1. Primary creep: A rapid initial deformation that slows down over time.
  2. Secondary creep: A steady rate of deformation.
  3. Tertiary creep: Accelerated deformation leading to failure.

Factors Influencing Creep:

• Temperature: Higher temperatures increase atomic mobility, accelerating creep.
• Stress: Higher applied stress results in faster creep.
• Material Composition: Materials with a more tightly bonded atomic structure (like metals with higher melting points) exhibit slower creep.

(ii) Brinelling:

Brinelling refers to the permanent indentation or damage that occurs on a hard surface when it is subjected to excessive localized pressure, usually by a hard, stationary object pressing against it. This often occurs in bearings or mechanical contacts.

Action:

• When a hard object (such as a ball bearing) exerts excessive pressure on a softer material, it creates indentations or marks (brinells) on the surface. These indentations may lead to increased friction and wear over time.
• Brinelling typically occurs when the bearing or contact surface is subjected to a static or repeated load beyond its design limits, often during high-pressure contact.

(iii) Fretting:

Fretting is the wear and degradation that occurs at the interface of two materials under small oscillatory movements or vibrations. These movements cause repeated micro-sliding or rubbing, leading to material removal and surface damage.

Action:

• Small relative movements between contacting surfaces cause localized wear, leading to the formation of debris and wear particles. The areas in contact experience high friction and wear, resulting in surface degradation. Over time, this can lead to fatigue and cracking in the material.
• Fretting is most common in situations where there is a slight movement between two components under load, such as in bearing races or gear interfaces.

(iv) Fretting Corrosion:

Fretting corrosion is the combination of mechanical wear and electrochemical corrosion at the interface of two materials, where small oscillatory movements occur. The wear process exposes fresh surfaces to air or water, and the material at the contact point becomes prone to corrosion due to the creation of micro-galvanic cells.

Action:

• The fretting motion removes protective oxide films on the surfaces, exposing fresh metal, which reacts with moisture or oxygen to form corrosion products.
• This results in localized corrosion at the fretting contact areas, which accelerates wear and degradation. The corrosion can be particularly damaging if the environment is corrosive, such as in marine or industrial applications.

As Second Engineer, I would oversee the extensive welding repairs required for the vessel's rudder using the following plan:

Manual Metal Arc Welding (MMAW), also known as Shielded Metal Arc Welding (SMAW), is the most suitable process for this repair. The reasons are threefold:

• MMAW is highly portable, allowing for on-site repair within the drydock. The process is adaptable to various welding positions (downhand, overhead, horizontal, vertical) – a necessity given the complex geometry of a rudder.
• Assuming the rudder is constructed from standard steel, MMAW using readily available flux-coated electrodes provides good control, arc stability, and penetration. The flux coating protects the weld pool from atmospheric contamination during cooling.
• MMAW requires relatively simple equipment and is less demanding in terms of operator skill compared to other processes like TIG or MIG. This translates to cost-effectiveness and allows for a wider pool of qualified welders.
• If cast steel components are present, pre-heating will be necessary to minimize stress cracking, and specialized electrodes suited for the specific cast steel grade must be selected.

During welding by the metal arc process, the following points must be observed:

• Electrode Consumption Rate
• Penetration
• Slag Control
• Arc Length and Sound

1. Undercut: A groove formed along the edge of the weld bead, weakening the joint. Caused by excessive current, incorrect electrode angle, excessive travel speed, or improper electrode manipulation.

2. Overlap: Molten weld metal flows over the parent metal without proper fusion. Caused by low current, slow travel speed, excessive arc length, or improper joint preparation.

3. Slag Inclusion: Trapped slag within the weld metal, reducing its strength and potentially causing cracking. Caused by insufficient cleaning between passes, incorrect current, long arc length, slow travel speed, or too large an electrode diameter.

4. Incomplete Penetration: The weld does not fully fuse the joint faces, resulting in a weak joint. Caused by insufficient current, incorrect joint preparation (too small a root gap or bevel angle), excessive travel speed, or too large an electrode diameter.

• A thorough visual examination of all welds to identify any surface defects like cracks, porosity, or lack of fusion.
• NDT methods such as Magnetic Particle Inspection (MPI) or Dye Penetrant Inspection (DPI) will be employed to detect subsurface flaws that may not be visible during visual inspection. The specific NDT method chosen will depend on the type of steel and the accessibility of the weld areas.
• The repaired rudder will undergo a hydrostatic pressure test. This involves filling the rudder with a water head of 2.46 meters and observing for any leaks. This confirms the watertight integrity of the welds and the overall rudder structure.

• A bolt with a diameter slightly larger than the flange coupling bore diameter (D + 0.00025D) is selected.
• A push rod (loading rod) is inserted into the hollow coupling bolt, and a hydraulic head is attached.
• Hydraulic oil pressure of approximately 30,000 N/m² is applied, causing the bolt to stretch (approximately 0.021mm) and temporarily reduce its diameter by 0.00025D. This allows easy insertion of the bolt into the flange bore.
• The bolt is placed inside the bore by hand, and the nut is tightened and nipped up using a spanner.
• The hydraulic pressure is then released, allowing the bolt to expand and create a secure interference fit within the bore. This generates a tensile stress of approximately 15.5 tons/m², ensuring a firm grip.
• After fitting, the hydraulic assembly (items A, B, and C) is removed, and a protective plastic cap is placed over the bolt head.

• The hollow bolt design allows precise control of the bolt load, ensuring optimal tightening and load distribution.
• Diametrical re-expansion after hydraulic pressure release ensures a strong interference fit of the shank within the flange bore, reducing the risk of loosening.
• Hollow coupling bolts are easier to remove for inspection and maintenance, significantly reducing dismantling and fitting time.
• Unlike traditional bolts, hollow coupling bolts minimize wear on the bore, eliminating the need for frequent re-machining.
• Replacement of hollow coupling bolts is less frequent, reducing operational downtime and maintenance costs.

The pneumatic relay operates on the principle of a nozzle-flapper arrangement. Air supply pressure acts on a diaphragm located below a spring. A rod and plug, connected to the diaphragm, control the flow of output air through a nozzle. A flapper is positioned near the nozzle.

Operation:

1. An input signal (which can be a change in pressure or displacement of the flapper) affects the flapper's position.
2. Flapper movement changes the distance between the flapper and the nozzle. A decrease in distance (flapper closer to the nozzle) restricts the output airflow. Conversely, an increase in distance increases output airflow. This is the direct action of the relay.
3. Changes in the output air flow alter the back pressure at the nozzle.
4. Increased nozzle back pressure pushes the diaphragm downwards, compressing the spring and further reducing the output airflow. Decreased nozzle back pressure allows the spring to push the diaphragm upwards, increasing output airflow.
5. A portion of the output air is fed back through a line connected to a bellows and a feedback-adjusting spring (as shown in the sketch). This feedback pressure acts against the diaphragm, opposing the effect of the input signal. The bellows and spring arrangement allow the system to fine-tune the feedback strength. This negative feedback stabilises the system and increases the control range, preventing excessive overshoot or oscillation. The feedback mechanism subtracts from the effective input pressure, acting as a negative feedback loop.

Mw * r * ω^2 > ρw * g * h

where Mw is the mass of water, r is the impeller radius, ω is angular velocity, and ρw is water density. For air, due to its lower density, the centrifugal force Ma * r * ω^2 is too low to overcome the gravitational force needed for lift, resulting in no suction lift.

On the other hand, turbo-blowers, also centrifugal machines, can handle air because the required centrifugal force is feasible for the lower density of air. In turbo-blowers, the centrifugal force:

Ma * r * ω^2 > ρa * g * h

is sufficient for moving air, allowing effective operation with gases.

• Confirm that the NPSH does not exceed 4.5 meters as per regulations to avoid cavitation and ensure effective suction.
• Place fire pumps as low as possible in the ship to ensure consistent water availability.
• The pump should have a reliable priming device, such as a water ring primer or air eductor type, to remove air from the suction line.
• Maintain a sufficient water level in the priming tank to enable efficient priming.
• Ensure proper functioning of the spring-loaded valve to maintain suction.
• Strictly follow the Planned Maintenance System (PMS) for both the fire pump and the priming device to ensure they are in optimal working condition.

There are 2 solenoid valve which opens during the start of the pump (Check the diagram below). 7 bar air keeps flowing through the air eductor. Eductor creates vacuum and takes out air from our pump casing and water floods into the pump casing. When the pressure transmitter senses the discharge pressure above a certain level, the solenoid valve closes.

In a CPP-based system, the propeller blades’ pitch is controlled using a non-rotating servo motor housed within the gear housing. The servo motor operates based on input from the bridge:

• Movement of the bridge lever moves the servo control valve piston, allowing hydraulic oil to flow into the appropriate side of the servo piston via the servo control block and check valve.
• The force generated on the servo piston is transmitted via a push-pull piston rod inside the propeller shaft to the crosshead and crank mechanism in the gear housing.

This design enables the blade pitch to adjust, allowing the water flow direction to change as needed for thrust or reverse thrust.

Support for Strength of Thrust and Reverse Thrust:

• Solid plate: Strengthens the bottom of the tunnel.
• Centre girder: Provides longitudinal support to the tunnel from underneath.
• Foot brackets: Reinforce the tunnel and prevent flexing under stress.
• Tunnel ends: Welded to the hull plating or fabric piece using butt welding, integrating the tunnel into the vessel structure for increased rigidity and durability.

• Diesel engine
• Single-speed induction motor (e.g., a squirrel cage induction motor).

Reasons for Suitability of an Induction Motor:

1. The CPP system allows pitch adjustment, so the motor does not need to stop during maneuvering operations. The propeller blades can be placed at neutral pitch when no thrust is required.
2. Induction motors are reliable and require less maintenance.
3. Equipped with either a star-delta starter or an electronic soft starter, ensuring smooth operation and minimal wear on components.
4. The motor provides uninterrupted power, allowing precise and efficient control of thrust direction and strength

Osmosis is the natural flow of solvent (water) from a dilute solution to a more concentrated one across a semi-permeable membrane, which stops the dissolved salts but allows water molecules to pass. In a sea water container the pure water would migrate into the sea water, diluting it and building up a hydrostatic head equal to the osmotic pressure of the sea water.

Reverse osmosis simply reverses this natural flow. A pressure greater than the osmotic pressure is applied to the concentrated side (sea water) by a high-pressure pump. This forces water molecules through the semi-permeable membrane in the opposite direction, i.e. out of the sea water and away from the salt, leaving fresh water on the low-pressure side. The applied pressure is typically 40-70 bar for sea water, well above the natural osmotic pressure of roughly 25-28 bar. The membrane passes water but retains the dissolved salts, minerals, bacteria and colloidal matter, so the permeate (product water) is either potable or can be polished. The concentrated brine is discharged overboard.

Components in series:

Sea water feed -> feed/sea water pump and strainer -> multi-media/dual media filter -> cartridge filter(s) -> high-pressure booster pump -> membrane pressure vessel (spiral wound RO membranes in series/parallel) -> two outlets: permeate (fresh water) to product/storage tank and brine/concentrate to a flow control valve and overboard. A dosing/metering pump adds anti-scalant and chlorine/bisulphite. A product meter and conductivity/TDS monitor on the permeate line.

Sea water is first strained and filtered through dual-media and cartridge filters to remove suspended solids, sand and organic matter that would foul or block the membranes. Anti-scalant is dosed to prevent carbonate and sulphate scale precipitating on the membrane surface. The filtered water is pressurised to 50-70 bar by the high-pressure pump and fed into the membrane pressure vessels.

In the pressure vessel the sea water is split by the spiral-wound semi-permeable membranes into two streams. The permeate, which passes through the membrane, flows to the centre collecting tube and out to the product tank; this is the drinking water. The concentrate (brine), which has not passed through the membrane, leaves the vessel and its flow is regulated by a back-pressure/concentrate control valve, which also sets the operating pressure and the recovery ratio. In a single-pass system the permeate quality is normally sufficient at moderate salinity; the conductivity cell monitors and diverts poor product to bilge or recirculates. Anti-scalant dosing, membrane cleaning and regular filter backwashing maintain output and protect the membranes.

(a) Explaining Creep, Brinelling, Fretting, and Fretting Corrosion:

Creep:

• Creep is the time-dependent permanent deformation of a material under sustained stress at elevated temperatures. It occurs at stresses significantly below the material's yield strength. The rate of creep depends on material properties, temperature, time under load, and the applied stress. Creep progresses in three stages: primary (decreasing rate), secondary (constant rate), and tertiary (rapidly increasing rate leading to failure). An example is the creep of a turbine blade, causing it to contact the casing and fail.

Brinelling:

• Brinelling is the formation of permanent indentations on a hard surface due to heavy or repeated impact loads over a small area. This can occur during standstill or rotation and is often caused by improper installation (e.g., of bearings). Even small indentations can lead to malfunctions like chattering or vibration, accelerating other wear mechanisms. The hardness of materials needs to be considered during design to prevent brinelling.

Fretting:

• Fretting is surface wear between two contacting surfaces under load and small-amplitude cyclic motion (vibrational wear). It's common in bolted or keyed joints where relative movement is unintended. Fretting initiates fatigue cracks, leading to fatigue failure. The severity depends on factors like displacement amplitude, load, material properties, number of cycles, and lubrication. Lubricant is often squeezed out from between the surfaces during the cyclic movement, resulting in direct metal-to-metal contact.

Fretting Corrosion:

• Fretting corrosion is a specific type of fretting wear that involves chemical reactions between the contacting surfaces. The repeated rubbing and microscopic movement leads to the formation of oxides and other corrosion products, exacerbating the wear and leading to more severe damage than fretting alone. This process is typically accelerated in the presence of moisture or other corrosive environments.

Boiler Water Level Controller – Float Operated Type

A simple float-operated water level controller consists of:

• A float chamber connected to the boiler steam drum by two lines — one for steam and one for water.
• A float inside the chamber, which rises and falls with changes in water level.
• A mechanical linkage or rod attached to the float, which extends to an electric sensor unit mounted above the chamber.

Working Principle:

• As the float moves up or down, it shifts a contactor along a variable resistance track or magnetic switches.
• This movement changes the electrical output signal, which is sent to a square-root converter.
• The converter transforms the electrical signal into a proportional pneumatic signal.
• The pneumatic signal acts on the diaphragm of the feed water control valve actuator, modulating feed flow to maintain the set water level.

Reasons for Using a Float-Operated Type

1. Reliability: Unlike constant/variable head leg systems, there is no need to maintain a filled reference column.
2. Simplified Installation: Electrical sensing eliminates the need for long impulse tubes for remote indication.
3. Ease of Maintenance: The electric sensor unit can be easily replaced without dismantling the float chamber.
4. Lower Cost: Fewer mechanical parts and no head leg piping reduce installation and maintenance expenses.

Explanation of Terms (Analogy with Controller and Boiler)

: In this system, the float is the detecting element. It directly senses the water level, which is the controlled variable, and its movement provides a signal that represents the current state of the system.

: The square root converter and the feedwater controller collectively act as the servo motor. They are the mechanisms that receive the signal from the detecting element and perform the physical action (opening or closing the feedwater valve) to correct the water level.

: The set point is the desired value. This is a fixed input to the square root converter (or a comparator) that represents the ideal water level that the system aims to maintain. The controller continuously works to match the actual water level to this desired value.

Conditions that Promote Microbial Growth:

• Presence of water
• Availability of nutrients
• Favourable temperature (25-40°C) and pH (8-9)
• Oxygen (depending on the type of microbes)

Indications of Microbial Degradation:

• Rotten egg-like smell due to gas production
• Slimy oil appearance, often with peeling paint inside the crankcase
• Black staining on white metal bearings, pins, and journals
• Excess water and sludge accumulation after purification
• Frequent filter plugging
• Corrosion on unprotected surfaces

Sources of Microbial Contamination:

• Distillate fuel
• Lube oil itself
• Cooling systems, bilge, retention tanks, and ballast tanks
• Contaminated bunkered oil

Effects of Microbial Degradation:

• Corrosive damage to bearings and journals due to acid production
• Increased water content in the oil, challenging to remove by purification
• Filter blockages and restricted flow
• Deterioration in oil properties, such as viscosity and pH
• Reduced heat transfer in coolers

Prevention of Microbial Degradation:

• Regular draining to avoid water accumulation
• Maintain ideal temperature conditions to inhibit microbial growth
• Avoid water contamination in the oil
• Regular testing and correct operation of purification systems
• Use biocides or fungicides, as recommended by oil suppliers

Correct Sampling for Shore-Based Testing:

1. Always use the same sampling location, ideally in the main supply line just before the entry to the main engine.
2. Drain a sufficient amount of oil before collecting a sample.
3. Rinse the new container with oil before collection.
4. Draw samples only after the engine has been running at normal operating conditions.
5. Fully seal and label the sample with the date, vessel name, running hours, oil grade, and sampling point identification.

(b) Abnormal Water Content: High water content indicates water ingress into the system, potentially due to leaks in piston cooling pipes, heat exchangers, or cylinder liners, or purifier malfunction.

Action:

• Locate and repair the source of the water ingress.
• Drain the water after allowing sufficient time for settling.
• Use the purifier to remove remaining water and contaminants.
• Consider batch purification for more thorough cleaning.

Abnormal TBN (Total Base Number): Low TBN suggests the oil's alkalinity is depleted. This can be caused by water ingress or microbial contamination.

Action:

• Remove contaminants through purification.
• Depending on the severity, replenish or completely renew the oil. Consider the potential need for a complete oil change if the contamination is severe.

• A bolt with a diameter slightly larger than the flange coupling bore diameter (D + 0.00025D) is selected.
• A push rod (loading rod) is inserted into the hollow coupling bolt, and a hydraulic head is attached.
• Hydraulic oil pressure of approximately 30,000 N/m² is applied, causing the bolt to stretch (approximately 0.021mm) and temporarily reduce its diameter by 0.00025D. This allows easy insertion of the bolt into the flange bore.
• The bolt is placed inside the bore by hand, and the nut is tightened and nipped up using a spanner.
• The hydraulic pressure is then released, allowing the bolt to expand and create a secure interference fit within the bore. This generates a tensile stress of approximately 15.5 tons/m², ensuring a firm grip.
• After fitting, the hydraulic assembly (items A, B, and C) is removed, and a protective plastic cap is placed over the bolt head.

• The hollow bolt design allows precise control of the bolt load, ensuring optimal tightening and load distribution.
• Diametrical re-expansion after hydraulic pressure release ensures a strong interference fit of the shank within the flange bore, reducing the risk of loosening.
• Hollow coupling bolts are easier to remove for inspection and maintenance, significantly reducing dismantling and fitting time.
• Unlike traditional bolts, hollow coupling bolts minimize wear on the bore, eliminating the need for frequent re-machining.
• Replacement of hollow coupling bolts is less frequent, reducing operational downtime and maintenance costs.

• R-134a: Suitable for medium and high-temperature applications, serving as a long-term replacement for R-12.
• R-404A: Suitable for low and medium-temperature applications.
• R-407C: A replacement for R-22, suitable for medium and high-temperature applications.
• R-410A: Twice as efficient as R-22 but generally recommended for new systems only.

During Normal Operation:

• Implement a robust monitoring system with daily logs of key parameters to allow for early detection of any anomalies, such as pressure drops or temperature fluctuations, that might indicate a leak.
• Regular Leak Detection: Conduct routine leak tests to identify leaks from joints, seals, gaskets, pipes, and other components.
• Safety Valve Management: Ensure correct setting and operation of safety valves to prevent accidental refrigerant release.

During Maintenance Activities:

• Mandate the complete recovery and recycling of refrigerant gas before any maintenance work commences. Utilize onboard recovery systems, ensuring they are properly maintained and calibrated.
• Implement procedures to minimize refrigerant venting during maintenance, utilizing capturing and recovery techniques wherever possible.
• Provide comprehensive training to all maintenance personnel on proper handling, recovery, and recycling procedures for refrigerants.
• Maintain a clean, dry system to prolong mechanical seal effectiveness and prevent leaks. Avoid excessive water pressure in the condenser to prevent tube failures. Monitor machinery vibration to prevent damage that could lead to gas leaks.
• Use leak-proof connections for charging and recovery, employing compatible and manufacturer-specified gaskets and mechanical seals. Ensure all refrigerant is recovered before opening the system for maintenance.
• Use geniune Spare parts to avoid any failure of system leading to accidentally release of gas.

According to SOLAS chapter - 2, part 1, regulation 29.16, every tanker of more than 10,000 GT shall comply with the following:

• The main steering capability due to a single failure in any part of one of the power actuating systems shall be regained in not more than 45 seconds.
• The main steering shall comprise at least two identical power actuating systems, each capable of meeting the requirements. Loss of fluid from one system shall be capable of being detected, and the defective system shall automatically get isolated so that the other system shall remain fully operational

Considering the above regulatory requirements, given below is a “Fail Safe steering gear” suitable for use on a tanker of more than 100,000 T DWT.

Shown in the diagram is a “Fail safe steering gear” having two independent power actuating systems that can

• Work simultaneously in normal operation, meeting the requirement OR
• Work independently and meet the requirement
• In the event of loss of fluid from any one system, it can be detected and isolated automatically so that the other system can remain fully operational.

Working:

• The system incorporates two sets of electric-driven pumps. Both main and auxiliary pumps are on the same shaft. The main pump shown in the diagram is a variable delivery pump
• The variable delivery pump takes suction from the tank and supplies hydraulic oil to the ram cylinders. The oil flow of the pump is determined by the pump actuating lever
• The movement of the pump actuating lever is controlled by the rudder angle order given by the bridge with the help of a bi-directional control valve
• A two-way shock relief valve is fitted between the two cylinders to release the pressure from one side of the cylinder to the other side in case of pressure increase in one of the cylinders due to heavy seas
• By-pass valves are also fitted between two cylinders, which are normally shut during operation. When one system is stopped, there is a pressure drop, as the auxiliary pump has also stopped this opens the by-pass valves, thus removing the hydraulic lock of the ram operation.
• Auto isolation valves in the system are there to isolate one system in case of any failure.

Sequence of events during hydraulic oil leak:

Case 1: Consider an oil leak from any pipe for cylinders 1 and 2 with the No. 1 pump running:

1. No. 1 tank level will come down to L1, and it will sound an alarm on the bridge and in ECR
2. When the tank level further drops to L2, i.e. low-low level, the no. 1 pump stops.
3. Stopping the No. 1 pump also stops the attached auxiliary pump. So the line pressure drops, due to which the normally closed by-pass valves ‘X’ and ‘Y’ open.
4. Simultaneously, the auto isolation valves ‘A’, ‘B’ and ‘C’ will be operated by an electric signal. A, B and C are normally open valves. The electric signal will close them. So, systems 1 and 2 will be completely separated. Thus, the defective system, I.e. system 1, is isolated.
5. Along with the operation of the auto isolation valves, the No. 2 pump will start automatically. The attached auxiliary pump will act on the by-pass valve ‘Y’ and close it. This enables cylinders 3 and 4 to be in normal operation.
6. It should also be noted that since system 1 is completely isolated, there is no oil pressure to operate the bypass valve. So the by-pass valves remain open, thereby removing the hydraulic lock for the ram movement in cylinders 1 and 2

Case 2: Consider an oil leakage from any pipe of cylinders 3 and 4 with the No. 1 pump running:

Points 1, 2 and 3 are the same as case 1

1. Simultaneously, the auto isolation valves ‘A’, ‘B’ and ‘C’ will be operated by an electric signal. This will shut the normally open valves A, B and C. Thus, systems 1 and 2 will be completely separated
2. Along with the operation of auto isolation valves, the No. 2 pump will start automatically. The attached auxiliary pump will act on the by-pass valve ‘Y’ and close. So, cylinders 3 and 4 will come into normal operation.
3. Now, since the leak is between the pipe of cylinders 3 and 4, the level of the no. 2 tank will drop to L1 and give an alarm.
4. The level will further drop to L2, but the pump will not stop and changeover to ensure that the leak is from the pipe of cylinders 3 and 4
5. When the no. 2 tank level drops to L3, the no. 2 pump stops and the no. 1 pump starts to operate the steering using cylinders 1 and 2
6. Starting the no. 1 pump will ensure that the by-pass valve ‘X’ is shut, and stopping the no. 2 pump will ensure that the by-pass valve ‘Y’ is open

This ensures the operation of the steering Gear with the defective system fully isolated.

The pneumatic relay operates on the principle of a nozzle-flapper arrangement. Air supply pressure acts on a diaphragm located below a spring. A rod and plug, connected to the diaphragm, control the flow of output air through a nozzle. A flapper is positioned near the nozzle.

Operation:

1. An input signal (which can be a change in pressure or displacement of the flapper) affects the flapper's position.
2. Flapper movement changes the distance between the flapper and the nozzle. A decrease in distance (flapper closer to the nozzle) restricts the output airflow. Conversely, an increase in distance increases output airflow. This is the direct action of the relay.
3. Changes in the output air flow alter the back pressure at the nozzle.
4. Increased nozzle back pressure pushes the diaphragm downwards, compressing the spring and further reducing the output airflow. Decreased nozzle back pressure allows the spring to push the diaphragm upwards, increasing output airflow.
5. A portion of the output air is fed back through a line connected to a bellows and a feedback-adjusting spring (as shown in the sketch). This feedback pressure acts against the diaphragm, opposing the effect of the input signal. The bellows and spring arrangement allow the system to fine-tune the feedback strength. This negative feedback stabilises the system and increases the control range, preventing excessive overshoot or oscillation. The feedback mechanism subtracts from the effective input pressure, acting as a negative feedback loop.

Reverse osmosis (RO) is a process that purifies water by forcing it through a semi-permeable membrane. In this process, high pressure is applied to a solution with a high concentration of dissolved solids, such as saltwater, on one side of the membrane. This pressure overcomes the natural osmotic pressure, causing the pure water molecules to pass through the membrane while leaving behind the larger salt ions and other impurities. The membrane acts as a selective barrier, allowing only the water to pass, while the concentrated brine solution is discarded. For large-scale production, a large membrane surface area and a strong pump capable of generating high pressures are necessary.

1. Pretreatment Stage

Pretreatment is essential to protect the R.O. membranes from fouling and scaling.

• Scaling: Caused by soluble salts such as calcium carbonate and calcium sulphate depositing on the membrane.
• Fouling: Caused by micro-organisms, metal oxides, and colloidal particles coating the membrane surface.

Pretreatment methods include:

• Mechanical filtration: Multiple filter stages in series, e.g.:
  • Sand filters
  • Multi-layer filters
  • Microfilters (<10 ppm particle size)
• Chemical treatment:
  • Coagulants for fine particle removal
  • Biocides to kill micro-organisms
  • Acid dosing to neutralize calcium salts and prevent scale formation

  A pump takes suction from the sea chest through a coarse filter, delivering water at about 6 bar through the pretreatment system.

  2. High-Pressure Stage

  • A high-pressure piston pump raises the feed water pressure to above 50 bar.
  • This pressurized water enters the semi-permeable membrane modules.

  3. Separation Process

  • Due to the pressure difference between the concentrated brine side and the permeate side, water molecules pass through the membrane.
  • Dissolved salts, organics, and microbes are rejected.

  Outputs:

  • Permeate (Fresh Water): Low-salt content water used for drinking and domestic purposes.
  • Brine (Concentrated Reject): Discharged overboard (OVBD).

  4. Post-Treatment

  The fresh water (permeate) is further treated to make it suitable for shipboard use:

  • Hardness adjustment (to prevent excessive softness)
  • pH correction (maintained around 8 for taste and corrosion control)
  • Chlorination (for disinfection)

  Note: If pH rises too high, chlorine’s effectiveness against micro-organisms is reduced.

  Flow Summary:

  Sea Water → Coarse Filter → Pretreatment Filters & Chemicals → High-Pressure Pump → R.O. Membranes →

  → Permeate (Fresh Water) → Post-treatment → Ship’s Fresh Water System

  → Brine (Reject Water) → Overboard

In a CPP-based system, the propeller blades’ pitch is controlled using a non-rotating servo motor housed within the gear housing. The servo motor operates based on input from the bridge:

• Movement of the bridge lever moves the servo control valve piston, allowing hydraulic oil to flow into the appropriate side of the servo piston via the servo control block and check valve.
• The force generated on the servo piston is transmitted via a push-pull piston rod inside the propeller shaft to the crosshead and crank mechanism in the gear housing.

This design enables the blade pitch to adjust, allowing the water flow direction to change as needed for thrust or reverse thrust.

Support for Strength of Thrust and Reverse Thrust:

• Solid plate: Strengthens the bottom of the tunnel.
• Centre girder: Provides longitudinal support to the tunnel from underneath.
• Foot brackets: Reinforce the tunnel and prevent flexing under stress.
• Tunnel ends: Welded to the hull plating or fabric piece using butt welding, integrating the tunnel into the vessel structure for increased rigidity and durability.

• Diesel engine
• Single-speed induction motor (e.g., a squirrel cage induction motor).

Reasons for Suitability of an Induction Motor:

1. The CPP system allows pitch adjustment, so the motor does not need to stop during maneuvering operations. The propeller blades can be placed at neutral pitch when no thrust is required.
2. Induction motors are reliable and require less maintenance.
3. Equipped with either a star-delta starter or an electronic soft starter, ensuring smooth operation and minimal wear on components.
4. The motor provides uninterrupted power, allowing precise and efficient control of thrust direction and strength

To: The Technical Superintendent,

xxx Ships Ltd., Singapore.

Subject: Inspection Report on Safety Equipment - M.V. xxx

As a newly appointed Second Engineer onboard a 20-year-old vessel currently in dry dock, my priority is to ensure that all safety equipment complies with the relevant regulations and survey requirements. Below is a detailed inspection process covering Fire-Fighting Equipment (FFA) and Life-Saving Appliances (LSA):

Fire-Fighting Equipment:

• Fire Control Plan: The fire control plan was found to be in good condition and correctly positioned throughout the vessel.
• Fire Detection System: The fire detection system was tested and found to be fully operational. All alarms activated as expected.
• Fire Hose, Nozzles & Hydrants: A complete inspection of fire hoses, nozzles, and hydrants was conducted. One defective hose was identified and replaced. All hydrants were successfully exercised and are now free-flowing.
• Fixed CO2 System: The fixed CO2 system underwent a thorough inspection, including a complete line blow-through. All alarms were tested and functioned correctly. Pressure levels were checked and found within acceptable parameters.
• Portable & Non-Portable Fire Extinguishers: All portable and non-portable fire extinguishers were inspected, and their condition verified against available maintenance records. All extinguishers were found to be fully charged and in good working order.
• Remote Shutdowns & Ventilation: The remote shutdown capabilities for fans, operation of deck discharge valves, and remote operation of ventilation dampers were all successfully tested and verified as fully functional.
• Fireman's Outfit & SCBA: The fireman's outfit, including SCBA bottles and compressor, were inspected and found to be in satisfactory condition, with sufficient air pressure confirmed in cylinders.
• Spare Parts: A sufficient quantity of spare parts for fire-fighting equipment was verified.

Life-Saving Equipment:

• Lifeboats & Davits: The condition of the lifeboats, davits, and embarkation arrangements were thoroughly examined. All davits were successfully exercised.
• Lifeboat Engine & Spares: The lifeboat engine was tested and found to be operational. Sufficient spare parts for the lifeboat engine were verified as present. Battery condition and charging system were checked and deemed satisfactory.
• Liferafts: The condition of each liferaft and its securing arrangements were checked; all were found to be securely fastened and in good condition.
• Lifejackets & Immersion Suits: A sufficient quantity of lifejackets and immersion suits, as per regulations, were verified and found to be in good condition.
• Emergency Lighting: Emergency lighting at muster stations, embarkation points, and all necessary escape routes was tested and confirmed operational.
• EPIRB, SART, GMDSS, & Communication Systems: The operational functionality of the EPIRB, SART, GMDSS equipment (including the VHF radio and PA system) and general alarm were successfully verified.
• Muster List & Duties: The muster list and assigned duties were reviewed and updated as necessary.
• Location of LSA: The location of all life-saving appliances (LSA) was verified against the onboard plans.
• Maintenance & Testing Records: All maintenance and testing records for both fire-fighting and life-saving equipment were reviewed and found to be adequately maintained and compliant.

The overall condition of the safety equipment onboard M.V. xxx is satisfactory, with only minor maintenance issues addressed during this inspection. The vessel's safety arrangements are largely compliant with current regulations. I await your instructions regarding any further required maintenance or modifications.

Thanking You,

Yours Faithfully,

2nd Engineer

M.V. xxx

Special Features of Valve Lid and Seat:

• The seat's design deflects escaping steam towards the valve lid's lip, boosting the valve's lift. This increases the efficiency of steam release.
• The pressure of escaping steam acting on a piston provides extra lift to the valve. This helps in a faster, more complete opening.
• A loose pin secures the valve lid, allowing for thermal expansion without stress.

Overhauling the Boiler Safety Valve:

Safety:

• Carry out a Toolbox meeting, Risk assessment and Permit to work.
• Ensure that the internal pressure of the boiler is fully relieved before attempting to remove the safety valve. Wear appropriate personal protective equipment (PPE), including safety glasses, to protect against residual fluid splashes.

Disassembly Steps:

• Remove the seal and pull out the split pin.
• Detach the fork lever.
• Loosen the set screw and remove the cap.
• Remove the spindle lock nut and adjusting screws from the spring cover (make a mark on the position of the adjusting screw and spring cover for easy reassembly).
• Take off the spring cover.
• Remove the nut connecting the yoke with the body, then lift the block composed of the yoke, upper spring, and lower spring carrier along with the spring.
• Pull out the spindle.
• Remove the disc.
• Loosen the screw and remove the valve seat.

Checks:

• Inspect the valve seat and disc for damage; lap if necessary.
• Check the sliding surface of the floating piston for dirt and foreign materials, cleaning thoroughly.
• Assess the condition of the spindle for trueness.
• Inspect the body for rust and corrosion.
• Examine the spring for cracks and measure its free length.
• Verify the working of the easing gear.
• Ensure the drain line is clear.
• Conduct non-destructive testing of components as needed.
• Check the condition of the blowdown ring and the compression ring neck bush.

Clearances to be measured:

• Measure the clearance between the valve lip and the seat lip.
• Clearances between spindle and cap nut
• Measure the clearance between the cotter pin and the groove in the spindle.
• Check the clearances between the floating piston and the spindle
• Check the lift after assembly. It should be more than D/16 for high lift safety valve

Swell:

• The sudden rise in steam demand may cause a fall in steam pressure and the saturation temperature. Due to this, the water temperature at this moment may become higher than the saturation temperature.
• The drop in saturation temperature will cause the formation of bubbles and will raise the boiler water level, which is termed as ‘swell effect’
• The control system will shut the feed water control valve due to the swell effect when actually the amount of water has decreased. So water level may further decrease.

Shrink:

• When the steam supply becomes normal, the saturation temperature rises, and the formation of steam bubbles drop
• This will drop the water level in the drum, and the control system will open the feed water control valve.
• Due to the introduction of cold water, steam bubbles will collapse, causing a further drop in water level, which is termed as the ‘shrink effect’
• If the feed controller is unable to sense the phenomenon, there could be too high water level.

In split control, two conditions are generally managed:

• Start-up valve fully open at lower loads to handle minimal flow requirements.
• Start-up valve closed at higher loads, with the main valve fully handling the feed water supply.

In split control, a single controller is used for more than one final control element making the control process more effective and at low cost.

A condensing chamber (or condensing pot) is used in boiler drum level measurement systems with differential pressure transmitters to improve accuracy at high pressure and temperature. The chamber cools and condenses steam into water within the measuring line so that the differential pressure transmitter senses hydrostatic pressure of water only (excluding steam pressure variations). It is located at the end of the impulse lines connected to the boiler drum, usually near the transmitter. The condensing chamber stabilizes the measurement by preventing steam from entering the impulse line and causing measurement errors due to temperature and density changes.

(a) Safematic Concept

The Safematic system is an automatic safety arrangement provided in steering gear hydraulic systems to detect and isolate hydraulic oil leakage, thereby preventing complete loss of steering capability.

Need for Safematic

In the event of:

• Burst hydraulic pipe
• Failure of seals or fittings

There is a risk of rapid oil loss, which could otherwise result in total steering failure and loss of vessel maneuverability.

Working Principle

• Sensors continuously monitor the oil level in the hydraulic expansion tanks.
• If a sudden drop in oil level is detected, indicating a leakage:
  • The Safematic system automatically divides the hydraulic system into two independent circuits.
  • The leaking circuit is identified and isolated.

  Result

  • The faulty side is shut down.
  • The remaining healthy pump and actuator continue to operate.
  • At least 50% steering capability is retained, ensuring compliance with SOLAS safety requirements.

  (b) Flow Reversal of Main Hydraulic Pump

  Modern steering gears employ bi-directional variable delivery pumps, such as:

  • Swash plate pump
  • Hele-Shaw pump

  Instead of using directional control valves, rudder direction is changed by reversing the hydraulic oil flow directly at the pump.

  Method of Flow Reversal

  • Changing the tilt direction of the swash plate reverses the piston stroke.
  • This reverses oil flow to either side of the steering ram, causing the rudder to move port or starboard.

  Advantages

  1. Smooth Operation
     • Eliminates sudden shocks caused by opening and closing heavy directional valves.
  2. Higher Efficiency
     • Reduces pressure losses associated with complex valve manifolds and piping.
  3. Simplicity and Reliability
     • Removes directional control valves, which are common failure points.
  4. Better Control Response
     • Direct pump control provides faster and more accurate rudder movement.

  (c) Flow Volume Variation of Hydraulic Pump

  The speed of rudder movement depends on the volume of hydraulic oil delivered to the steering ram.

  Method to Achieve Flow Variation

  Flow variation is achieved by altering the swash plate angle in a variable delivery pump.

  Operating Conditions

  1. Neutral Position
     • Swash plate is vertical (zero angle).
     • Pistons rotate but do not stroke.
     • No oil flow → Rudder remains stationary.
  2. Maximum Flow
     • Swash plate is tilted to a larger angle (θ).
     • Piston stroke length increases.
     • Maximum oil displacement occurs, producing maximum rudder speed.
  3. Variable Flow
     • Intermediate swash plate angles provide proportional oil flow.
     • Enables smooth acceleration and deceleration of the rudder.

  Benefit

  • Provides soft starts and stops
  • Prevents mechanical stress
  • Enhances steering accuracy and comfort

  (d) Hunting Lever Functioning

  The hunting lever is a mechanical feedback mechanism that:

  • Prevents rudder overshoot
  • Ensures the rudder stops exactly at the commanded angle

  Functioning

  Input Signal

  • When the bridge wheel or telemotor is operated:
    • One end of the hunting lever is displaced.
    • This moves the pump control rod, initiating oil delivery.

    Feedback Mechanism

    • As the rudder moves:
      • Its actual position is mechanically fed back to the other end of the hunting lever.

      Hunting Action

      • Rudder movement pulls the lever in the opposite direction.
      • When the commanded angle is reached:
        • The hunting lever returns the pump control rod to neutral (zero delivery).
        • Oil flow stops and the rudder holds position.

Fatigue is progressive and localised structural damage caused by cyclic loading, where the maximum stress is below the ultimate tensile strength. The relationship between stress level, cyclic frequency, and operating life depends on whether the fatigue is high-cycle/low-stress or low-cycle/high-stress.

High-cycle fatigue (low stress-high cycle):

• This occurs at lower stress levels over a high number of cycles, resulting in elastic deformation. The component can withstand more cycles at these lower stress levels, and its life expectancy is determined by the S-N curve, which predicts the number of cycles before failure at a given stress level. For example, fatigue in turbocharger blowers often results from prolonged vibration over numerous cycles.

Low-cycle fatigue (high stress-low cycle):

• This occurs at high-stress levels over fewer cycles, causing plastic deformation in the material. This type of fatigue is typically assessed by a strain curve. If the stress level increases, the component's operating life decreases, as higher stress accelerates the onset of failure. For example, air receivers filling automatically face high stress and experience fewer cycles before failure.

If stress levels or the number of cycles increase beyond the material’s capacity, failure will occur sooner. It is important to keep stress levels within allowable limits for extended component life.

• Surface roughness, porosity, inclusions, and abrupt section changes all create stress concentrations, lowering fatigue strength.
• Coarse grain size, specific chemical compositions, and cold working introduce residual stresses that reduce fatigue resistance.
• Corrosion, erosion, and decarbonisation weaken the material and accelerate fatigue crack initiation and propagation.
• Faulty workmanship during assembly or processing introduces defects that may significantly shorten the component's life.

• Cylinder overload due to excess power puts excessive stress on the girders.
• Incorrect crankshaft alignment induces uneven loading and stress concentrations.
• Material defects, high residual stresses in welds, heat-affected zone hardening, and the presence of dissolved oxygen all reduce fatigue resistance.
• Tank top deformation from pressurisation or overheating adds stress to the bedplate.

To minimise the risk of fatigue cracking:

(i) Constructional strength:

• Bed plates are made up of M.S. plates with four steel casting, which are assembled and welded together so that the bed plate is strong longitudinally & transversely with good resistance to twisting along its length.
• Longitudinal strength is obtained by fabricating each side of the bed plate in the form of a box girder.
• The cast steel cross girder in which the main bearing is placed contributes to the bed plate's transverse strength and resistance against twisting along its length.
• Resin cast chocks are used between the bedplate and the double bottom tank top to absorb the shocks & stress.

(ii) Maintenance:

• Monthly checks on the bolt tension.
• Monthly checks on engine load using power cards & measuring cylinder peak pressure.
• Regular checking of tension for main bearing jack bolts as recommended by engine manufacturers.
• Regular checks on crankshaft alignment by taking deflection & compare with recommended value.
• By maintaining engine operations at specified load, temperature, pressure, speed, etc.

Pump rooms on tankers are required to be mechanically ventilated. The ventilation system must be of the exhaust type and designed to prevent the accumulation of flammable vapors. To ensure this, the system needs to have a minimum capacity of 20 air changes per hour based on the gross volume of the space. The exhaust fans must be a non-sparking type, and the air ducts should be arranged to provide effective ventilation throughout the entire space. The discharge from the exhaust fans must be led to a safe location on the open deck.

Cargo tanks are ventilated to make them "gas free," which means removing flammable or toxic vapors. This can be achieved using portable fans or blowers. These fans must be constructed to prevent incendiary sparking, for example, if the impeller were to touch the casing. The fans must also have sufficient capacity and penetration to quickly gas-free the entire tank atmosphere.

Alternatively, on tankers equipped with an Inert Gas System (IGS), the system itself can be used for ventilation. To do this, the connection from the scrubber tower is closed, an air inlet from the atmosphere is opened, and the IGS blowers are started. This process effectively ventilates the cargo tanks by drawing in fresh air and pushing out the existing atmosphere.

The International Convention for the Safety of Life at Sea (SOLAS) 1974 mandates specific protections for cargo tanks to ensure safety. These include:

• Pressure/Vacuum Valves (P/V valves): These valves protect the tanks from over- or under-pressurization, which could lead to structural damage.
• Overfill Alarms and Shutdowns: To prevent spills and environmental pollution, tanks must be equipped with alarms that signal when a tank is nearing its maximum capacity. In some cases, these are linked to automatic shutdown systems.
• Corrosion Protection: Measures are taken to prevent corrosion, which can weaken the tank structure and lead to leaks.

Inert gas systems that use an inert gas generator are equipped with several alarms to monitor their safe and proper operation. These additional alarms include:

• High Casing Temperature Trip: This alarm activates if the temperature inside the generator casing becomes excessively high, indicating a potential malfunction.
• Low Lubricating Oil Pressure Trip: The system will alarm and trip if the lubricating oil pressure drops below a safe level, which could cause damage to the generator's internal components.
• Low/No Flow Scrubber Water: This alarm alerts the crew if there is insufficient water flow to the scrubber, which is essential for cooling the gas and removing sulfur dioxide and other impurities.

The stern frame, being a structural component, can exhibit a few defects during a dry-dock inspection. Minor damage might include cracks in the brackets that connect the propeller post and shoe piece or in the upper end of the rudder horn hanging from the stern. Major damage, often caused by grounding or impacts, includes fractures, bending, or twisting of the shoe piece. Surveyors also need to check for corrosion and deterioration of zinc anodes typically fitted to the stern frame and rudder, as they required in reducing galvanic corrosion.

The sea chest is prone to structural and functional defects due to its exposure to seawater. Typical issues include cracks in the welds of girders, floor plates, or around pipe ends, as well as corrosion and marine growth on the internal and external surfaces. Internal coatings may peel off, and sacrificial anodes might be worn out. Additional faults include fouling or choking of pipes and the deterioration of sea chest valves, often caused by pitting or corrosion.

The bilge keel, which helps reduce rolling, can develop cracks in welded joints or experience partial detachment. Other common faults include corrosion on the surface, dents in plates, or twisting and bending (kinks). Cracks at the ends of the bilge keel are also common due to stress concentration points.

Sacrificial anodes are inspected for wear or detachment. Worn-out anodes can no longer protect the ship's structure from galvanic corrosion, so replacements may be necessary. Detached anodes compromise the ship's cathodic protection system.

The rudder is inspected for cracks or dents in the side or top plates, which could lead to water ingress. Issues with pintles, such as fractures, corrosion, wear of sleeved bushes, or damage to threads, are also common. Inspectors look for loose portable boxes installed above or below the gudgeon (if applicable). Corrosion, paint fouling, and surface roughness on the rudder plates must be addressed, and any twisting or bending of the rudder stock is evaluated for necessary repairs.

The oily bilge is drawn into the separator by the automatic self-priming pump. The pump is located on the outlet of the separate to prevent the formation of a mechanical emulsion. As the oily bilge water enters the separator, it flows upwards through the matrix plate pack towards the top of the separator. Some oil separates immediately due to the reduced flow velocity and the difference in specific gravity between oil and water. Oil droplets impinge on the surface of the matrix plate pack and begin the coalescing process. The oil droplets coalesce until they become large enough to detach from the corrugated plates and gravitate to the top of the separator. Smaller oil droplets that escape the matrix plate pack are removed by the polishing pack. After the separated oil accumulates to a predetermined level, the oil sensor initiates the oil discharge and cleaning cycle by stopping the pump, closing the water discharge valve and opening the clean water inlet valve. This allows clean sea or fresh water to cleanse the matrix plate pack and flow upward in the reverse direction, washing the polishing pack and displacing the accumulated oil. The outlet of the Oily Water Separator is directed by a 3-way valve either to the overboard or to the storage tank. The valve is controlled by a 15ppm monitor, which allows overboard discharge if oil content is below 15 ppm and stops discharge if oil content is exceeded.

• Probe Too Low: The sensor might not detect the actual oil level. This can lead to the frequent opening of the water discharge valve, allowing water to escape into the oil outlet, contaminating the separated oil.
• Probe Too High: The oil discharge valve will open late, reducing the separation efficiency. This is because the oil and water will mix more thoroughly before the valve opens, leading to a less effective separation of the two liquids.

(a) Advantages of Using Steam Turbine Propulsion for LNG Carriers

Steam turbine propulsion offers the following advantages for vessels carrying LNG cargo:

1. Utilisation of boil-off gas (BOG): LNG naturally evaporates during the voyage, producing boil-off gas. This gas can be used directly as boiler fuel, helping to control cargo tank pressure and avoiding wastage of the gas.
2. No need for a boil-off gas re-liquefaction plant: Since the natural boil-off gas can be consumed in the boilers, there is no need for energy-intensive and complex re-compression or re-liquefaction arrangements.
3. Fuel flexibility: Steam boilers can operate on natural gas, heavy fuel oil (HFO), marine gas oil (MGO), or a combination of these fuels, providing good operational flexibility.
4. Increased cargo space / reduced fuel storage requirement: As boil-off gas from the cargo can be used as fuel, the vessel does not need to carry excessive quantities of conventional fuel oil, allowing more space to be available for cargo.
5. High reliability and low maintenance: Steam turbines have fewer moving and no heavy reciprocating parts. This results in less wear and tear, reduced frictional losses, lower lubricating oil consumption, and less frequent maintenance.
6. Smooth and quiet operation: Steam turbines provide continuous rotary motion, resulting in low noise and vibration, reduced hull vibration and fatigue, and improved crew comfort.
7. Cleaner combustion: LNG burns relatively cleanly, producing very low sulphur emissions and fewer deposits compared with conventional heavy fuel oil.
8. Simple gas combustion arrangement: Unlike internal-combustion gas engines, steam boilers do not require precise high-pressure gas admission timing and are not affected by problems such as engine knocking.
9. Lower gas pressure: Gas can be supplied to the boilers at relatively low pressure, reducing the hazards associated with high-pressure gas fuel systems.
10. Good redundancy: LNG steam plants are commonly arranged with more than one boiler. If one boiler is shut down for maintenance or becomes unavailable, the vessel can continue operating with the remaining boiler(s).

(b)(i) Safety Precautions for Gas Pipeline Supplying the Boiler and Burning Gas in the Boiler

• Gas pipelines must not pass through accommodation spaces, service spaces, or control stations, unless fully compliant with regulations.
• Fuel piping to be designed to comply with SB – 1/6 of steel vessel rules.
• Maximum pressure in the fuel gas supply line to not exceed 10 bar.
• All pipelines to be welded; flanged connections only permitted at equipment connections.
• Gas-tight compartments containing fuel piping should have direct access to the open deck.
  • If not possible, access via gas-safe spaces must be through self-closing gas-tight doors.
• Compartments to be fitted with mechanical exhaust ventilation.
• Gas detection systems to be fitted in the compartment and boiler room.
• Incorporate block and bleed valve arrangement in pipelines to comply with purging requirements.
• Entire pipeline supplying methane gas to machinery spaces to be double-walled (annular type) and purged with nitrogen before and after gas-burning operations.
• Nitrogen gas pressure in annular space to be maintained; leakage alarms to be activated if methane detected.
• Boiler room fitted with methane gas sensors with alarm and venting arrangements.
• Boiler room to be continuously ventilated with methane monitoring in air.
• Boiler room separated from machinery space by air-lock antechamber with self-closing doors.

(b)(ii) Means of Getting Rid of Excess Gases During Loading or Discharge

• Cooldown process is carried out to prevent excessive boil-off during loading/discharge.
• Cooldown achieved by supplying liquid methane to spray headers via a distribution grid, directed to various tank levels as required.
• Boil-off vapour is passed through a high-duty compressor back to shore via the vapour return line.
• When liquid is detected at the tank bottom, cooldown is considered complete.
• Primary insulation and secondary barrier temperatures maintained between –80°C to –100°C.
• Tank pressure is controlled using compressors and by varying liquid flow to spray headers.
• Before starting loading, the shore flow for cooldown is gradually reduced.
• After cooldown, loading starts slowly and increases gradually to full rate.
• Tank pressures are monitored; maximum loading rate is governed by compressor capacity to return vapour to shore.

As Second Engineer, I would oversee the extensive welding repairs required for the vessel's rudder using the following plan:

Manual Metal Arc Welding (MMAW), also known as Shielded Metal Arc Welding (SMAW), is the most suitable process for this repair. The reasons are threefold:

• MMAW is highly portable, allowing for on-site repair within the drydock. The process is adaptable to various welding positions (downhand, overhead, horizontal, vertical) – a necessity given the complex geometry of a rudder.
• Assuming the rudder is constructed from standard steel, MMAW using readily available flux-coated electrodes provides good control, arc stability, and penetration. The flux coating protects the weld pool from atmospheric contamination during cooling.
• MMAW requires relatively simple equipment and is less demanding in terms of operator skill compared to other processes like TIG or MIG. This translates to cost-effectiveness and allows for a wider pool of qualified welders.
• If cast steel components are present, pre-heating will be necessary to minimize stress cracking, and specialized electrodes suited for the specific cast steel grade must be selected.

During welding by the metal arc process, the following points must be observed:

• Electrode Consumption Rate
• Penetration
• Slag Control
• Arc Length and Sound

1. Undercut: A groove formed along the edge of the weld bead, weakening the joint. Caused by excessive current, incorrect electrode angle, excessive travel speed, or improper electrode manipulation.

2. Overlap: Molten weld metal flows over the parent metal without proper fusion. Caused by low current, slow travel speed, excessive arc length, or improper joint preparation.

3. Slag Inclusion: Trapped slag within the weld metal, reducing its strength and potentially causing cracking. Caused by insufficient cleaning between passes, incorrect current, long arc length, slow travel speed, or too large an electrode diameter.

4. Incomplete Penetration: The weld does not fully fuse the joint faces, resulting in a weak joint. Caused by insufficient current, incorrect joint preparation (too small a root gap or bevel angle), excessive travel speed, or too large an electrode diameter.

• A thorough visual examination of all welds to identify any surface defects like cracks, porosity, or lack of fusion.
• NDT methods such as Magnetic Particle Inspection (MPI) or Dye Penetrant Inspection (DPI) will be employed to detect subsurface flaws that may not be visible during visual inspection. The specific NDT method chosen will depend on the type of steel and the accessibility of the weld areas.
• The repaired rudder will undergo a hydrostatic pressure test. This involves filling the rudder with a water head of 2.46 meters and observing for any leaks. This confirms the watertight integrity of the welds and the overall rudder structure.

A coil-operated brake for winches and deck machinery is designed to automatically adjust the braking force in response to changes in the load on the mooring line. This system ensures the correct force is applied between the brake band and the winch drum at all times.

The core principle is that when an additional load is applied to the mooring line, the line stretches, which in turn loosens the tightening mechanism. This loosening action automatically causes the brake to apply the correct force, maintaining constant tension. This has the significant advantage of being a self-adjusting system, meaning that once it's set, there's no need for a crew member to periodically re-apply the recommended torque. The brake is typically released using a hydraulic lever.

When a vessel is riding at anchor, a mechanism is used to lock the anchor chain and relieve the windlass of the strain. This is crucial for preventing damage to the windlass and ensuring the anchor is securely held.

A Cable stopper, often a pawl of a rod, is engaged with a link of the anchor chain. The pawl acts as a stop, preventing the chain from moving. All the weight and force from the anchor and the vessel's movement are then transferred to this locking device and the ship's structure, effectively relieving the windlass of any strain.

Brinell Hardness Test: This Test determines the hardness of a material by measuring its resistance to indentation.

Testing method:

• A hardened steel or tungsten carbide ball of diameter (D) is placed on the material's surface.
• A test load (F) is applied to the ball for a predetermined time.
• After removing the load, the diameter of the impression (d) is measured using a specialized microscope.

The Brinell Hardness Number (BHN) is calculated using the formula:

$$BHN \space = \space {{2F} \over \pi D (D - \sqrt{D^2 - d^2})} $$

where:

• F = Applied load in kgf
• D = Ball diameter in mm
• d = Diameter of the indentation in mm

Advantages:

• Provides an accurate measure of hardness.
• Particularly useful for testing materials with rough surfaces.

Limitations:

• Leaves a permanent impression on the material.
• Requires optical measurement of the impression diameter, which can be challenging.

1. Liquid Penetrant Inspection (Non-Destructive Test)

There are two different types, such as:

In the Fluorescent Dye method, after applying Dyes and viewing under ultra-violet light, any fault can be found by the glow of the penetrant in them.

In the Aerosol Dye method, the first cleaning bottle is applied on the surface for cleaning purposes and the second bottle of Dye follows to soak and enter into any flaws or cracks. Afterwards, the last bottle of Developer (or chalky sediment) is applied to reveal any faults on the component under test.

The liquid penetrant process is comparatively simple as no electronic system is involved, and the equipment necessary is cheaper than that required for other N.D.T systems. The major limitation of this method is that it can detect surface breaking only. The method is not suitable for use with naturally porous materials such as unglazed ceramics.

2. Ultrasonic testing (Non-Destructive Test)

The probe of the test equipment transmits high-frequency sound waves about 0.5 MHz to 20 MHz, which are reflected by any flaws in the object, and these reflected sound waves are then displayed on the monitor screen of the cathode ray oscilloscope.

Ultrasonic tests are suitable for the detection, identification and size assessment of a wide variety of both surface and sub-surface defects in materials.

The ultrasonic method can be used to measure the thickness of the material or to detect internal or surface defects in welds, casting or forging either during manufacture or when in service.

Leakage of treated boiler water (through a leaking blowdown pipe, valve, water tube, or circulating pump) and excessive blowdown both lead to a loss of treated water. Replacing this lost water with untreated makeup water dilutes the TDS and chemical reserves.

Action:

• Inspect all boiler blowdown pipes and valves for leaks and repair as necessary.
• Check for leaks in water tubes (indicated by white smoke from the funnel). Repair any leaks found.
• Inspect circulating pumps for leaks and repair as necessary.
• Once leaks are repaired, add chemicals to restore the desired levels.
• Monitor boiler water conditions through frequent testing.

(ii) Reduction in phosphate reserve, with an increase in chlorides and total dissolved solids:

Seawater ingress is the likely culprit. Seawater contamination introduces carbonates, sulfates, and chlorides of sodium, calcium, and magnesium. These ions react with phosphate in the boiler, forming non-scale sludge, leading to reduced phosphate reserves and increased chlorides and TDS.

Action:

• Identify and plug any leaky condenser tubes causing seawater ingress.
• Inspect and replace sacrificial anodes if necessary. This helps prevent corrosion.
• Increase the frequency and duration of boiler water blowdown.
• If chloride levels remain high, reduce boiler load to 2/3 normal output, blow down to minimum level, and refill with fresh make-up water.
• A complete emptying and flushing of the boiler is the ultimate solution to remove the remaining contamination. Carry out this at the earliest opportunity.

(iii) Reduction in alkalinity reserve only:

• Seawater contamination potentially introduces acidic products that neutralize the alkaline reserve.
• Boiler water leakage (loss of alkaline water).
• Oil contamination (oil can react to reduce alkalinity).
• Ingress of air (air can lead to the formation of acidic products that neutralize alkalinity).

Actions:

• Identify and rectify any seawater ingress.
• Maintain a high hotwell temperature to prevent air ingress.
• Identify and repair any boiler water leaks.
• Identify and eliminate the source of oil contamination.

(iv) Increase in oxygen levels only:

• Poor performance of the de-aerator, allowing oxygen to remain in the feedwater.
• Insufficient hydrazine reserves (hydrazine is an oxygen scavenger).
• Low hotwell temperature (oxygen is more soluble in colder water).
• Leaking feed water pump gland (allowing air to enter).

Actions:

• Inspect and repair any faults in the deaerator.
• Ensure adequate hydrazine reserves are maintained.
• Maintain a high hotwell temperature.
• Identify and repair any gland seal leaks in the feed water pump.

• Complete data allows for the identification of subtle trends indicating developing problems. A gradual decrease in alkalinity, for example, might not immediately exceed the alarm threshold but could signal a developing issue that can be addressed proactively.
• Comparing current results to past results helps establish a baseline and allows for easier detection of anomalies.
• Complete data provides more context during troubleshooting. If a problem arises, having access to a complete history can help identify the root cause more effectively.
• Logged data enables proactive adjustments and repairs before faults escalate, preventing boiler damage and reducing unplanned downtime.

Pump rooms on tankers are required to be mechanically ventilated. The ventilation system must be of the exhaust type and designed to prevent the accumulation of flammable vapors. To ensure this, the system needs to have a minimum capacity of 20 air changes per hour based on the gross volume of the space. The exhaust fans must be a non-sparking type, and the air ducts should be arranged to provide effective ventilation throughout the entire space. The discharge from the exhaust fans must be led to a safe location on the open deck.

Cargo Tank Ventilation

Cargo tanks are ventilated to make them "gas free," which means removing flammable or toxic vapors. This can be achieved using portable fans or blowers. These fans must be constructed to prevent incendiary sparking, for example, if the impeller were to touch the casing. The fans must also have sufficient capacity and penetration to quickly gas-free the entire tank atmosphere.

Alternatively, on tankers equipped with an Inert Gas System (IGS), the system itself can be used for ventilation. To do this, the connection from the scrubber tower is closed, an air inlet from the atmosphere is opened, and the IGS blowers are started. This process effectively ventilates the cargo tanks by drawing in fresh air and pushing out the existing atmosphere.

The primary problem with carrying LNG is maintaining its extremely low temperature of approximately -160°C. Despite the insulated tanks, a small amount of the LNG will inevitably vaporize, a phenomenon known as "boil-off." This boil-off must be managed, as it poses a safety risk and represents a loss of cargo. The process of managing this boil-off is critical and consumes a significant amount of power if the gas is to be reliquefied.

Several methods are used to handle boil-off gas on board LNG carriers:

• Reliquefaction: Heavy-duty compressors are used to compress the boil-off gas, converting it back into a liquid state and returning it to the cargo tanks.
• Mixed Refrigeration: A refrigeration process that uses a mixture of different refrigerants to cool and reliquefy the boil-off gas.
• Expander Cycle: A method that uses an expander to cool the boil-off gas, causing it to reliquefy.
• Using it as Fuel: The boil-off gas can be used as fuel for the ship's engines, either completely or as a partial fuel in a dual-fuel combustion system. This turns a potential problem into a source of power for the vessel.

Controllable Pitch Propellers (CPP)

It is preferable to house the main servomotor for a controllable pitch propeller (CPP) in the propeller hub rather than in the shafting forward of the propeller shaft. This design, known as a hub servo system, is preferred over the external servo system, which uses a long push-pull rod extending from the engine room. The primary reason for this preference is that the long push-pull rod in an external servo system is prone to bending. This bending can occur due to the rod's length and the significant water pressure acting against the propeller blades, which can compromise the pitch control mechanism's reliability and precision. Housing the servomotor directly in the hub eliminates the need for this long rod, resulting in a more robust and reliable system.

1. Hydraulic System Maintenance

• Periodic cleaning of hydraulic filters and oil coolers.
• Regular oil sampling (both onboard quick checks and shore analysis) to detect contamination or wear particles.
• Monitoring oil consumption to detect leaks in the system.

2. Mechanical Components

• Greasing all linkages to prevent corrosion and wear.
• Checking and lubricating moving parts as per manufacturer’s recommendations.

3. Operational Checks

• Ensuring familiarization of all relevant personnel with correct operating and maintenance procedures.
• Regular testing of alarms and safety devices.
• In dry dock, verify actual pitch position against remote indicators at the wheelhouse and engine room.
• Test the fail-safe arrangement to ensure it operates correctly in emergencies.

• R-134a: Suitable for medium and high-temperature applications, serving as a long-term replacement for R-12.
• R-404A: Suitable for low and medium-temperature applications.
• R-407C: A replacement for R-22, suitable for medium and high-temperature applications.
• R-410A: Twice as efficient as R-22 but generally recommended for new systems only.

During Normal Operation:

• Implement a robust monitoring system with daily logs of key parameters to allow for early detection of any anomalies, such as pressure drops or temperature fluctuations, that might indicate a leak.
• Regular Leak Detection: Conduct routine leak tests to identify leaks from joints, seals, gaskets, pipes, and other components.
• Safety Valve Management: Ensure correct setting and operation of safety valves to prevent accidental refrigerant release.

During Maintenance Activities:

• Mandate the complete recovery and recycling of refrigerant gas before any maintenance work commences. Utilize onboard recovery systems, ensuring they are properly maintained and calibrated.
• Implement procedures to minimize refrigerant venting during maintenance, utilizing capturing and recovery techniques wherever possible.
• Provide comprehensive training to all maintenance personnel on proper handling, recovery, and recycling procedures for refrigerants.
• Maintain a clean, dry system to prolong mechanical seal effectiveness and prevent leaks. Avoid excessive water pressure in the condenser to prevent tube failures. Monitor machinery vibration to prevent damage that could lead to gas leaks.
• Use leak-proof connections for charging and recovery, employing compatible and manufacturer-specified gaskets and mechanical seals. Ensure all refrigerant is recovered before opening the system for maintenance.
• Use geniune Spare parts to avoid any failure of system leading to accidentally release of gas.

Reverse osmosis (RO) is a process that purifies water by forcing it through a semi-permeable membrane. In this process, high pressure is applied to a solution with a high concentration of dissolved solids, such as saltwater, on one side of the membrane. This pressure overcomes the natural osmotic pressure, causing the pure water molecules to pass through the membrane while leaving behind the larger salt ions and other impurities. The membrane acts as a selective barrier, allowing only the water to pass, while the concentrated brine solution is discarded. For large-scale production, a large membrane surface area and a strong pump capable of generating high pressures are necessary.

1. Pretreatment Stage

Pretreatment is essential to protect the R.O. membranes from fouling and scaling.

• Scaling: Caused by soluble salts such as calcium carbonate and calcium sulphate depositing on the membrane.
• Fouling: Caused by micro-organisms, metal oxides, and colloidal particles coating the membrane surface.

Pretreatment methods include:

• Mechanical filtration: Multiple filter stages in series, e.g.:
  • Sand filters
  • Multi-layer filters
  • Microfilters (<10 ppm particle size)
• Chemical treatment:
  • Coagulants for fine particle removal
  • Biocides to kill micro-organisms
  • Acid dosing to neutralize calcium salts and prevent scale formation

  A pump takes suction from the sea chest through a coarse filter, delivering water at about 6 bar through the pretreatment system.

  2. High-Pressure Stage

  • A high-pressure piston pump raises the feed water pressure to above 50 bar.
  • This pressurized water enters the semi-permeable membrane modules.

  3. Separation Process

  • Due to the pressure difference between the concentrated brine side and the permeate side, water molecules pass through the membrane.
  • Dissolved salts, organics, and microbes are rejected.

  Outputs:

  • Permeate (Fresh Water): Low-salt content water used for drinking and domestic purposes.
  • Brine (Concentrated Reject): Discharged overboard (OVBD).

  4. Post-Treatment

  The fresh water (permeate) is further treated to make it suitable for shipboard use:

  • Hardness adjustment (to prevent excessive softness)
  • pH correction (maintained around 8 for taste and corrosion control)
  • Chlorination (for disinfection)

  Note: If pH rises too high, chlorine’s effectiveness against micro-organisms is reduced.

  Flow Summary:

  Sea Water → Coarse Filter → Pretreatment Filters & Chemicals → High-Pressure Pump → R.O. Membranes →

  → Permeate (Fresh Water) → Post-treatment → Ship’s Fresh Water System

  → Brine (Reject Water) → Overboard

Oil-Lubricated Stern Bearing System

The primary method for preventing seawater ingress into an oil-lubricated stern bearing system is a combination of mechanical seals and maintaining a balanced oil pressure. The system uses lip seals to contain the lubricating oil within the stern tube. An oil header tank ensures the oil pressure inside the stern tube is approximately equal to the surrounding seawater pressure. This balanced pressure prevents seawater from entering the stern tube.

Corrective Actions While Afloat

If the stern bearing system fails and seawater begins to ingress, the following temporary corrective actions can be taken while the vessel is still afloat:

• Switch to High-Viscosity Oil: The system can be recharged with a higher-viscosity oil. This thicker oil is less likely to leak past the seals, reducing the rate of seawater ingress.
• Install a Temporary Header Tank: Disconnect the regular oil supply line and connect a 45-gallon drum. This drum, supported by a block and tackle, acts as a temporary header tank with a variable head. The height of the drum can be adjusted by raising or lowering it to match the seawater pressure, ensuring the correct pressure balance is maintained.

Why Two Stern Bearing Oil Header Tanks Are Fitted

In some cases, two stern bearing oil header tanks are fitted, especially on vessels that experience large variations in draft, such as tankers. The two tanks are installed at different heights to accommodate these draft changes.

• The purpose is to match the oil pressure to the changing seawater pressure as the vessel's draft changes.
• By having tanks at different heights, the crew can switch between them to maintain the necessary differential pressure to keep seawater out of the stern tube. The maximum allowable pressure difference between the seawater and the oil is typically 0.3 bar.
• For example, the changeover between the tanks is often done at a specific draft, such as 11.7 meters.

Modern ships often use a single header tank with an air pneumatic system. This system automatically adjusts the oil pressure to match the seawater pressure based on the vessel's draft, eliminating the need for manual checks and tank changes.

According to SOLAS chapter - 2, part 1, regulation 29.16, every tanker of more than 10,000 GT shall comply with the following:

• The main steering capability due to a single failure in any part of one of the power actuating systems shall be regained in not more than 45 seconds.
• The main steering shall comprise at least two identical power actuating systems, each capable of meeting the requirements. Loss of fluid from one system shall be capable of being detected, and the defective system shall automatically get isolated so that the other system shall remain fully operational

Considering the above regulatory requirements, given below is a “Fail Safe steering gear” suitable for use on a tanker of more than 100,000 T DWT.

Shown in the diagram is a “Fail safe steering gear” having two independent power actuating systems that can

• Work simultaneously in normal operation, meeting the requirement OR
• Work independently and meet the requirement
• In the event of loss of fluid from any one system, it can be detected and isolated automatically so that the other system can remain fully operational.

Working:

• The system incorporates two sets of electric-driven pumps. Both main and auxiliary pumps are on the same shaft. The main pump shown in the diagram is a variable delivery pump
• The variable delivery pump takes suction from the tank and supplies hydraulic oil to the ram cylinders. The oil flow of the pump is determined by the pump actuating lever
• The movement of the pump actuating lever is controlled by the rudder angle order given by the bridge with the help of a bi-directional control valve
• A two-way shock relief valve is fitted between the two cylinders to release the pressure from one side of the cylinder to the other side in case of pressure increase in one of the cylinders due to heavy seas
• By-pass valves are also fitted between two cylinders, which are normally shut during operation. When one system is stopped, there is a pressure drop, as the auxiliary pump has also stopped this opens the by-pass valves, thus removing the hydraulic lock of the ram operation.
• Auto isolation valves in the system are there to isolate one system in case of any failure.

Sequence of events during hydraulic oil leak:

Case 1: Consider an oil leak from any pipe for cylinders 1 and 2 with the No. 1 pump running:

1. No. 1 tank level will come down to L1, and it will sound an alarm on the bridge and in ECR
2. When the tank level further drops to L2, i.e. low-low level, the no. 1 pump stops.
3. Stopping the No. 1 pump also stops the attached auxiliary pump. So the line pressure drops, due to which the normally closed by-pass valves ‘X’ and ‘Y’ open.
4. Simultaneously, the auto isolation valves ‘A’, ‘B’ and ‘C’ will be operated by an electric signal. A, B and C are normally open valves. The electric signal will close them. So, systems 1 and 2 will be completely separated. Thus, the defective system, I.e. system 1, is isolated.
5. Along with the operation of the auto isolation valves, the No. 2 pump will start automatically. The attached auxiliary pump will act on the by-pass valve ‘Y’ and close it. This enables cylinders 3 and 4 to be in normal operation.
6. It should also be noted that since system 1 is completely isolated, there is no oil pressure to operate the bypass valve. So the by-pass valves remain open, thereby removing the hydraulic lock for the ram movement in cylinders 1 and 2

Case 2: Consider an oil leakage from any pipe of cylinders 3 and 4 with the No. 1 pump running:

Points 1, 2 and 3 are the same as case 1

1. Simultaneously, the auto isolation valves ‘A’, ‘B’ and ‘C’ will be operated by an electric signal. This will shut the normally open valves A, B and C. Thus, systems 1 and 2 will be completely separated
2. Along with the operation of auto isolation valves, the No. 2 pump will start automatically. The attached auxiliary pump will act on the by-pass valve ‘Y’ and close. So, cylinders 3 and 4 will come into normal operation.
3. Now, since the leak is between the pipe of cylinders 3 and 4, the level of the no. 2 tank will drop to L1 and give an alarm.
4. The level will further drop to L2, but the pump will not stop and changeover to ensure that the leak is from the pipe of cylinders 3 and 4
5. When the no. 2 tank level drops to L3, the no. 2 pump stops and the no. 1 pump starts to operate the steering using cylinders 1 and 2
6. Starting the no. 1 pump will ensure that the by-pass valve ‘X’ is shut, and stopping the no. 2 pump will ensure that the by-pass valve ‘Y’ is open

This ensures the operation of the steering Gear with the defective system fully isolated.

(b) Advantages of a Vacuum Sewage System:

• The vacuum sewage system uses 85–90% less water for flushing compared to conventional systems, requiring very little flushing water.
• Toilets can be positioned more flexibly, including below the level of the holding tank, which is not feasible with gravity-fed systems.
• The system uses smaller diameter piping, reducing material and space requirements.
• The reduced water usage contributes to overall water conservation, making the system environmentally friendly.

• If the pump is pumping foam instead of liquid, this will be evident due to severe vibration. Add water to the tank and try again. If adding water does not help, reduce the level of foam by pouring antifoam agent into the tank (1 cup per 2 cubic metres of foam and sewage).
• Check that shut-off valves are fully open and not clogged.
• If the direction of rotation of the pump is wrong, change wiring accordingly.
• Close the valves that isolate the collecting unit from the piping system and start the pump again. If vacuum now builds up, there must be a leak in the piping system.