Question

With reference to Underwater Inspection in lieu of Dry docking (UWILD)

(a) Explain in detail, how an underwater survey is carried out. (6)

(b) State the requirements to be fulfilled before an underwater survey is acceptable to the survey authority. (5)

(c) Construct a list of the items in order of importance that the underwater survey authority should include. (5)

Answer 1

(a) An underwater survey, also known as Underwater Inspection in Lieu of Dry Docking (UWILD), involves a systematic and detailed examination of a vessel’s hull and underwater components while the ship remains afloat. The procedure includes the following steps:

The shipowner sends a request to the classification society surveyor, indicating the intention to perform an underwater survey.
A detailed plan of the ship's external hull features is submitted, showing the location of frames, bulkheads, welding lines, openings, etc.
The hull surface is cleaned before the survey to remove any marine growth or fouling that could obscure the inspection.
A diving company, approved by the classification society, is appointed to conduct the underwater inspection.

A self-propelled survey vehicle equipped with the following tools is used:

Long-Range Light TV Camera to aid in steering and checking hull deterioration.
High-resolution colour TV Camera to provide a close-up view of the hull coating and welded seams.
35mm Still Camera to capture still images.
Ultrasonic Probe for measuring plate thickness.
Depth Meter and Speed Indicator to provide accurate data on the vehicle's depth and movement.
Umbilical Cable to connect the survey vehicle to the survey boat, transmitting power and information.

The survey boat is to be equipped with:

A control console with TV monitors.
Plate thickness printouts.
Audio and video cassette recorders.
Playback units.
Diver communication systems.
Vehicle control systems and associated instruments.

Operation:

The survey vehicle is taken underwater by a diver to the survey starting point.
Using TV monitors and shell expansion plans as guides, the vehicle is navigated over the hull, focusing on the bottom structure, sides, stern frame, rudder, propeller, bilge keel, and hull openings.
All images, data, and information are recorded and transmitted back to the survey boat.
Detailed pictures of the stern frame, rudder, propeller, bilge keel, and hull openings are captured.
Divers are deployed to measure stern tube bearing wear, pintle clearance, and inspect stern seals, anodes, and rudder stock palm coupling bolts.
All recorded video and audio, including conversations between the surveyor and drivers, thickness printouts, measurements, and pictures are analyzed to determine the detailed underwater condition of the vessel.

(b) Before an underwater survey is accepted by the surveying authority, the following conditions must be met:

The vessel's owner submits a request to the surveyor, including:

The proposed date and location for the survey.
General information about the diving company.
A declaration that the vessel has not suffered any damage due to grounding, collision, or other incidents.

The ship's master or owner’s representative must provide a declaration confirming:

Any suspected or actual damage to the hull since the last dry-docking.
The underwater portion of the hull is protected by a suitable paint scheme that is of adequate thickness and remains valid until the next dry-dock.

The survey site should be in a protected area with calm and clear water, ensuring good underwater visibility. Attention must be given to the effects of currents and tides.
The hull must be clean for the external survey. The surveyor must be satisfied with the method and quality of the pictorial presentation, ensuring that it provides a reliable assessment of the hull's condition.
The underwater examination should be conducted by an approved diving company using closed-circuit TV and two-way communication, which can be monitored by the surveyor.
The vessel should be in as light an operating condition as possible to facilitate the survey.
Means must be available for the surveyor to examine the outside shell plating above the waterline.
Any required repairs identified during the survey must be carried out to the satisfaction of the attending surveyor.

(c) While the importance of each item may vary depending on the vessel and its specific requirements, below is a list of items that should be included in an underwater survey in order of importance:

Underwater Hull: General condition of the hull below the waterline.
Bottom and Shell Plating: Inspection for corrosion, damage, and fouling.
Shell Openings: Examination of openings such as sea chests, drain plugs, and overboard discharge points.
Stern Tube Oil Leaks: Check for leaks around the stern tube.
Propeller Blade: Inspection for damage, wear, and fouling.
Rudder: Inspection for damage, wear, and clearances.
Sea Chest Opening and Grating: Examination for blockages, damage, and fouling.
Anodes: Check the condition and effectiveness of cathodic protection anodes.
Bilge Keel: Inspection for damage and fouling.
Drain Plugs: Ensure all drain plugs are secure and in good condition.
Overboard Valve Openings: Check for proper operation and condition.
Forward Area: Inspection for any damage due to anchor and chain movement.

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