(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.