(a) Causes of Steering System Failure

Steering gear failures can be broadly classified into hydraulic, mechanical, electrical, and operational failures. The common causes are:

1. Hydraulic Oil Contamination

• Contamination by dirt, metal particles, or moisture causes hydraulic valves to stick, blocks control mechanisms, and results in severe wear of hydraulic pumps and components.

2. Air Entrapment in the Hydraulic System

• Air bubbles in the hydraulic oil cause oil hammering and erratic rudder movement.
• This may lead to pump cavitation, excessive vibration, and poor steering response.

3. Hydraulic Pipe Leakage

• Blown seals, ruptured hoses, or cracked pipelines result in a sudden loss of hydraulic pressure and fluid.
• As a result, the steering rams or actuators lose the power required to move the rudder.

4. Electrical Motor and Starter Failure

• Overheating, short circuits, phase failure, or faulty electrical relays may cause the steering motor to trip or burn out.

5. Control System Malfunctions

• Failure of communication between the bridge telemotor and the steering gear room.
• Malfunction of feedback devices such as potentiometers or encoders, resulting in incorrect rudder position indication.

6. Mechanical Wear and Tear

• Fatigue failure, shearing of the rudder stock, or damage to mechanical linkages such as crossheads and rams due to repeated heavy mechanical loading.

7. Power Supply Failure

• A blackout or failure of the main switchboard may prevent operation of the steering gear or delay the automatic transfer to the emergency power supply.

8. Rudder or Actuator Overload

• Operating at high speed in heavy weather can impose excessive torque on the rudder, overloading relief valves or permanently deforming steering gear components.

(b) Precautions in Design, Operation, and Maintenance

1. Design Precautions

• Redundancy: Provide at least two independent and identical power units for the main steering gear.
• Independent Systems: Arrange the main and auxiliary steering gear so that failure of one system does not render the other inoperative.
• Double-Walled Piping: Use double-walled or shielded high-pressure hydraulic piping to contain leaks and prevent oil spray onto hot machinery.

2. Operational Precautions

• Prompt Changeover: Ensure the crew is well trained in changing between manual, follow-up, and non-follow-up steering modes, and in transferring control from the bridge to the steering gear compartment.
• Routine Testing: As required by SOLAS Chapter V, carry out steering gear tests within 12 hours before departure, including emergency steering drills, and record the results.
• Parameter Monitoring: Continuously monitor hydraulic oil temperature, hydraulic oil level, phase failure alarms, and power supply condition.

3. Maintenance Precautions

• Hydraulic Oil Quality: Regularly sample and test hydraulic oil to remove contaminants and moisture, and replace filters at recommended intervals.
• Air Venting: Periodically bleed the hydraulic system to remove trapped air and maintain smooth steering operation.
• Inspection and Lubrication: Lubricate all moving parts regularly, inspect tie rods, and check hydraulic rams for pitting, scoring, and seal leakage.

(c) Tanker Requirements Introduced After Major Shipping Casualties

Following major tanker disasters such as the Amoco Cadiz (1978) and Exxon Valdez (1989), the IMO and classification societies introduced stricter steering gear and pollution prevention requirements.

1. Dual Independent Steering Power Units

• Tankers above 10,000 GT must be fitted with at least two independent power actuators.
• The steering gear must be capable of moving the rudder:
  • From 35° on one side to 35° on the opposite side, and
  • From 35° on one side to 30° on the opposite side within 28 seconds at maximum service speed.

  2. Emergency Power Supply

  • Tankers must be provided with an independent auxiliary steering gear or an emergency power supply capable of automatically restoring steering within 45 seconds after failure of the main power supply.

  3. Independent Control Systems

  • Main and auxiliary steering gear control systems must be arranged so that steering can be controlled from both:
    • The navigating bridge, and
    • The steering gear compartment.

    4. Double-Hull Construction

    • Following the Oil Pollution Act (OPA) 1990 and amendments to MARPOL, oil tankers are required to have double-hull construction to minimize oil pollution in the event of grounding or collision caused by steering failure.

    5. Voyage Data Recorder (VDR) and Steering Alarms

    • Tankers are required to carry a Voyage Data Recorder (VDR) to record steering commands and rudder responses.
    • SOLAS also mandates alarms for:
      • Low hydraulic oil level.
      • Hydraulic system overload.
      • Power supply or phase failure.