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Ship Steering gear failures and safeguards

The vital importance of the steering gear is reflected in the regulations of the government department with responsibility for shipping (usually Department of Transport or Coastguard) the requirements of the classification societies (Lloyd's Register, American Bureau of Shipping, Bureau Veritas and others) and the recommendations of the International Maritime Organization (IMO).

Measures against steering gear failure

Some general requirements for steering gears, based on the various regulations and SOLAS 1974, are given below:

(1) Ships must have a main and an auxiliary steering gear, arranged so that the failure of one does not render the other inoperative. An auxiliary steering gear need not be fitted, however, when the main steering gear has two or more identical power units and is arranged such that after a single failure in its piping system or one of its power units, steering capability can be maintained. To meet this latter alternative the steering gear has to comply with the operating conditions of paragraph 2 in the case of passenger ships while any one of the power units is out of operation. In the case of large tankers, chemical tankers and gas carriers the provision of two or more identical power units for the main steering gear is mandatory.

(2) The main steering gear must be able to steer the ship at maximum ahead service speed and be capable at this speed, and at the ship's deepest service draught, of putting the rudder from 35 deg on one side to 30 deg on the other side in not more than 28 secs. (The apparent anomaly in the degree of movement is to allow for difficulty in judging when the final position is reached due to feedback from the hunting gear which shortens the variable delivery pump stroke.) Where the rudder stock, excluding ice strengthening allowance, is required to be 120 mm diameter at the tiller, the steering gear has to be power operated.

(3) The auxiliary steering gear must be capable of being brought speedily into operation and be able to put the rudder over from 15deg on one side to 15deg on the other side in not more than 60 sees with the ship at its deepest service draught and running ahead at the greater of one half of the maximum service speed or 7 knots. Where the rudder stock (excluding ice strengthening allowance) is over 230 mm diameter at the tiller, then the gear has to be power operated.

(4) It must be possible to bring into operation main and auxiliary steering gear power units from the navigating bridge. A power failure to any one of the steering gear power units or to its control system must result in an audible and visual alarm on the navigating bridge and the power units must be arranged to restart automatically when power is restored.

(5) Steering gear control must be provided both on the bridge and in the steering gear room for the main steering gear and, where the main steering gear comprises two or more identical power units there must be two independent control systems both operable from the bridge (this does not mean that two steering-wheels are required).

When a hydraulic telemotor is used for the control system, a second independent system need not be fitted except in the case of a tanker, chemical carrier or gas carrier of 10000 gt and over. Auxiliary steering gear control must be arranged in the steering gear room and where the auxiliary gear is power operated, control must also be arranged from the bridge and be independent of the main steering gear control system. It must be possible, from within the steering gear room, to disconnect any control system operable from the bridge from the steering gear it serves. It must be possible to bring the system into operation from the bridge.

(6) Hydraulic power systems must be provided with arrangements to maintain the cleanliness of the hydraulic fluid. A low level alarm must be fitted on each hydraulic fluid reservoir to give an early audible and visual indication on the bridge and in the engine room of any hydraulic fluid leakage. Power operated steering gears require a storage tank arranged so that the hydraulic systems can be readily re-charged from a position within the steering gear compartment. The tank must be of sufficient capacity to recharge at least one power actuating system.

(7) Where the rudder stock is required to be over 230 rnm diameter at the tiller (excluding ice strengthening) an alternative power supply capable of providing power to operate the rudder, as described in paragraph 3 above, is to be provided automatically within 45 seconds. This must supply the power unit, its control system and the rudder angle indicator and can be provided from the ships emergency power supply or from an independent source of power located within the steering compartment and dedicated for this purpose. Its capacity shall be at least 30 minutes for ships of 1OOOOgt and over and 10 minutes for other ships.

Steering gear testing

Except in the case of ships regularly engaged on short voyages, the steering gear should be thoroughly checked and tested within 12 hours before departure. These tests should include testing of power unit and control system failure alarms, the emergency power supply (when relevant) and automatic isolating arrangements.

Every three months an emergency steering drill should be held and should include direct control from within the steering compartment at which time the use of the communications procedure with the navigating bridge should be practised.

Summarized below various ship steering gears general guideline:
  1. Ship Steering gear failures and safeguards

  2. The hydraulic circuit incorporates an arrangement of stop and bypass valves in the chest VC, which enable the gear to be operated on all four or on any two adjacent cylinders but not with two diagonally disposed cylinders. ......

  3. Four-ram electro-hydraulic steering gear mechanism

  4. The hydraulic circuit incorporates an arrangement of stop and bypass valves in the chest VC, which enable the gear to be operated on all four or on any two adjacent cylinders but not with two diagonally disposed cylinders. ......

  5. Enclosed hunting gear

  6. The light construction of the combined control and hunting gears is possible because the forces concerned are moderate. The self-contained unit is self-lubricating, and contained in an oil-tight case. ......

  7. Ship steering control mechanism- use of Hydraulic telemotor

  8. The telemotor has become, on many vessels, the stand-by steering control mechanism, used only when the electric or automatic steering fails. It comprises a transmitter on the bridge and a receiver connected to the steering gear variable delivery pump, through the hunting gear. ......

  9. Two-ram electro-hydraulic steering gear with variable delivery pumps

  10. An arrangement of a two-ram steering gear with variable delivery pumps may have a torque capacity of 120-650 kNm. The cylinders for this gear are of cast steel but the rarns comprise a one-piece steel forging with integral pins to transmit the movement through cod pieces which slide in the jaws of a forked tiller end. ......

  11. Rudder carrier bearing & Steering gear

  12. The rudder carrier bearing takes the weight of the rudder on a grease lubricated thrust face. The rudder stock is located by the journal beneath, also grease lubricated ......

  13. Small hand and power gears - Ship steering systems

  14. A simpler variant of the electro-hydraulic gear, for small ships requiring rudder torques below say, 150 kNm ......

  15. Four ram gear with servo-controlled axial cylinder pumps

  16. Variants of the servo-controlled swash plate axial cylinder pump are capable of working at 210 bar. Each pump is complete with its own torque motor, servo-valve, cut-off mechanism, shut-off valve and oil cooler. ......

  17. Vane type gear - provides security of four ram steering gear

  18. These may be regarded as equivalent to a two-ram gear, with torque capacities depending on size. An assembly of two rotary vane gears, one above the other, provides the security of a four ram gear. ......

  19. Details of two ram hydraulic steering gear arrangement

  20. When the main pumps are at no-stroke, the auxiliary pumps dischar. to the reservoir via a pressure-limiting valve PC20, set at 20 bar, and to t pump casings. When the main pumps are on-stroke, the auxiliary pump discharge to the main pump suction. ......

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