As discusses on one of my previous posts, there are different types of steering gear systems installed onboard vessels, from 4-ram type to rotary vane type. If you want to learn more about them please follow this link.

In accordance with IMO regulations the pumps, hydraulic power circuits and can and must operate as isolated systems, to allow for operation of the steering gear in the event of a vane or cylinder failure. The system can be so arranged that any one of the pumps can operate the system under failure of a cylinder or a vane.
This reduces the capacity of the steering gear by 50% and so the speed at which the rudder can turn is also reduced. Under such conditions the speed of the ship must be reduced in order to maintain maneuverability.

Moreover, in accordance with same regulations, the hydraulic pumps used in the steering gear are supplied with power from two independent sources. In the event of power failure from the main switchboard, one pump can be supplied from the emergency switchboard.

The control system operates automatically in the event of a hydraulic system failure and will operate the valves to isolate that part of the system which has failed, thus allowing one vane or one pump, depending of the steering gear type, to remain operational.

Usually, in the event of electrical failure the following alarms are activated:

• • • Overload alarm
    • Phase alarm
    • Steering control alarm

Failure of a running pump will produce auto start of the power unit selected for standby operation, that is why the second pump must be always on Stand-by mode while is not in operation.

In the event of oil leakage, the control system senses in which part of the system the leakage has occurred and will isolate that section of the hydraulic system, stopping the pump linked to that section if it is running and an alarms will trigger to warn the engineers that a failure has occurred. Under such circumstances only half of the steering gear capacity is available. Normally, the system is designed on the basis of “single failure”, but if all of the oil alarms are activated one power unit will still be running.

For example, in case of 4-ram type system, the auto-isolation system operates as follow to enable each pump unit to serve its intended purpose:

When one or the other pump are in service

• • • When leakage of working oil occurs due to oil-hydraulic piping failure, No.1 (No.2) oil tank level goes down and consequently the tank low level switch is actuated.
      The signal from the low level switch causes No.1 (No.2) isolation valve to automatically shut and No.1 (No.2) pump to stop running.
      At the same time, it causes No.2 (No.1) pump to start running, and also No.2 (No.1) isolation valve to shut.
      Simultaneously, the oil low level switch for visible and audible alarms is actuated, and an alarm sounds in the bridge and engine control room to announce the emergency.
    • With the steering operation continued in this state, if it is in No.1 (No.2) system that the oil-hydraulic piping failure has taken place, the oil level in No.1 (No.2) tank goes down to the point where the tank low-low level switch is actuated.
      The low-low level switch signal causes No.1 (No.2) isolation valve to open automatically and No.1 (No.2) pump to stop running. Consequently, the failed No.1 (No.2) system is isolated and No.2 (No.1) system is in operation to maintain 50% steering capability.
    • If it is No.2 (No.1) system that the oil-hydraulic piping failure has taken place, once the oil-hydraulic circuit has been separated by a signal from the No.1 oil tank low level switch, the oil level in the No.2 (No.1) oil tank goes down and consequently the No.2 (No.1) oil tank low level switch is actuated.

When both pumps are in use

• • • When leakage of working oil occurs due to oil-hydraulic piping failure, No.1 (No.2) oil tank level goes down and consequently the tank low level switch is actuated.
      The signal from the low level switch causes the No.1 and No.2 isolation valves to automatically shut.
      At the same time, it causes No.1 (No.2) pump to stop.
      At the same time, No.1 (No.2) isolation valve is opened and the No.2 (No.1) system is in operation to maintain 50% steering capability.
    • With the steering operation continued in this state, if it is in No.1 (No.2) system that the oil-hydraulic piping failure has taken place, the oil level in No.1 (No.2) oil tank goes down to the point where the tank low level switch is actuated.
      The No.1 (No.2) oil tank low level switch causes No.1 (No.2) isolation valve to open automatically and No.1 (No.2) pump to stop running.
      Consequently, the failed No.1 (No.2) system is isolated and No.2 (No.1) system is in operation to maintain 50% steering capability.
    • If it is in No.2 (No.1) system that the oil-hydraulic piping failure has taken place, the oil level in No.2 (No.1) oil tank goes down further to the point where the tank low-low level switch is actuated.
      The low-low level switch signal causes No.2 (No.1) isolation valve to open automatically and No.2 (No.1) pump to stop running.
      Consequently, the failed No.2 (No.1) system is isolated and then No.1 system with a combination of No.1 pump and No.1 and No.2 cylinders goes into operation to maintain 50% steering capability.

It is important to note that when the hydraulic oil piping failure causes the ‘Low’ level switch to be actuated, the isolation valve goes into operation to separate the oil hydraulic circuit into No.1 system and No.2 system, thereby reducing the steering capability to 50%. Therefore, upon sounding of the ‘Low’ level alarm, either promptly reduce the ship speed to a halt or, if the ship continues going full ahead, limit the steering angle to within 15°.

The method of control used for emergency steering depends upon the system or part of system which has failed. If it is only the bridge main steering unit that has failed the steering gear can be controlled from the steering gear room using the NFU-Tiller unit. This provides control of the steering gear, but there will be no backup or automatic change over of the pumps in the event of failure. For operation of the steering gear from the steering gear room the Location switch must be turned from the BRIDGE position to the STEERING GEAR local position.
When normal steering is resumed the switch must be returned to the BRIDGE position.

When using the NFU-Tiller control (if available) only one pump must be operated, as it is not possible to control two pumps simultaneously. The operator turns the tiller wheel or handle in order to turn the rudder according to instructions telephoned from the wheelhouse. The operator must watch the rudder angle on the steering indicator and take care not to over-steer.

An alternative to using the NFU-Tiller control is manual operation of the pump directional pilot valves, which are controlled by means of the directional push rods at the ends of the valves or the pushrod at the control pumps.

On some steering gear systems the operating pushrod must be pressed at the same time as the direction pushrod and both must be held in the “in” position whilst the rudder is turning. Both must be released together when turning of the rudder is to stop.

Pressing the directional pushrod and operating pushrod causes the directional pilot valve to send pressurized oil to the steering gear actuator, so that the rudder turns; pressing the push rod at the other end of the directional valve changes the direction of oil flow and the direction of rudder rotation. Release of the push rods at any point stops the oil flow and the rudder stops rotating.
When operating under emergency steering only one of the two or three pumps, depending of the steering gear system, may be operated and the associated directional pilot valve  is used to control the steering gear movement.

Instructions must be transmitted to the steering gear compartment from the bridge by telephone. It is essential that effective communication is maintained between the bridge and steering compartment at all times when operating under emergency steering. All personnel involved must be made fully aware of the need for communication in both directions between the bridge and steering gear compartment.

The procedures for emergency steering are as follows and should be read in conjunction with the illustration as exemplified above:

• • Proceed to the steering gear room and establish communications with the bridge either by radio or sound-powered telephone.
  • On the bridge, turn the non-follow-up switch unit on the
    maneuvering console to OFF.
  • In the steering gear room, turn the MANU-AUTO switch on No.1 and No.2 steering gear starter cabinets to MANUAL.
  • In the steering gear room, turn the POWER switch, for the auto-pilot to OFF position.
  • Go to either No.1 or No.2 emergency steering position.
  • Operate the emergency steering lever in accordance with instructions from the bridge. Direction arrows for PORT and STBD are usually located at the emergency steering position.
  • Observe the rudder angle on the rudder angle indicator. The figures on the rudder angle indicator are colour-coded for port (red) and starboard (green).

On some systems, in the event of serious damage the rudder can be locked by means of a device fitted below the steering gear actuator. The device is hydraulically actuated
by means of a separate pump unit, which is located in the steering gear compartment. The locking device exerts a torque of 20% of the steering gear torque. The main steering gear pumps cannot be operated when the locking device is activated and the locking device must be deactivated before the steering gear pumps can be started.

In conclusion, it is important to remember that when operating under emergency condition with only one pump in use the steering operation is limited.
For example, the rudder will move from 35° on one side to 30° on the other side in 46 seconds, which is slower than with two pumps operating, when a similar rudder movement is made in 23 seconds.
It must be notices that with slower operation of the rudder the steering of the ship is less effective than when operating with two pumps. The navigating officer must be aware that the vessel will not be as responsive to commands as when two pumps are operating.
When operating with one half of the steering gear, steering capability is maintained at a reduced ship operating speed of two thirds maximum, with 50% of the rudder torque available.

If you have any questions regarding above, please feel free to use our existing forum Seafarer’s World and will try to answer to all your queries.

If you like my posts, please don’t forget to press Like and Share. You can also Subscribe to this blog and you will be informed every time when a new article is published. Also you can buy me a coffee by donating to this website, so I will have the fuel I need to keep producing great content! Thank you!