Section 3 Construction and design

3.1.1 The entire steering gear is to be designed, constructed and installed to allow for a permanent transverse list of up to 15° and for ambient temperatures commensurate with the area in which the ship is to operate.

3.1.2 Rudder actuators are to be designed in accordance with the relevant requirements of Pt 5, Ch 9 Pressure Vessels other than Boilers for Class I pressure vessels (notwithstanding any exemptions for hydraulic cylinders).

3.1.3 Accumulators, if fitted, are to comply with the relevant requirements of Pt 5, Ch 9 Pressure Vessels other than Boilers.

3.1.4 The welding details and welding procedures are to be approved. All welded joints within the pressure boundary of a rudder actuator or connecting parts transmitting mechanical loads are to be of full penetration type or of equivalent strength.

3.1.5 The construction is to be such as to minimise local concentrations of stress.

3.1.6 The design pressure for calculations to determine the scantlings of piping and other steering gear components subjected to internal hydraulic pressure shall be at least 1,25 times the maximum working pressure taking into account any pressure which may exist in the low pressure side of the system.

3.1.7 For the rudder actuator, the permissible primary general membrane stress is not to exceed the lower of the following values:

3.1.8 No other consumers may be connected to the hydraulic steering gear drive unit.

3.2.1 Special consideration is to be given to the suitability of any essential component which is not duplicated. Any such essential component shall, where appropriate, utilize anti-friction bearings such as ball bearings, roller bearings or sleeve bearings which shall be permanently lubricated or provided with lubrication fittings.

3.2.2 All steering gear components transmitting mechanical forces to the rudder stock, which are not protected against overload by structural rudder stops or mechanical buffers, are to have a strength at least equivalent to that of the rudder stock in way of the tiller.

3.2.3 Actuator oil seals between non-moving parts, forming part of the external pressure boundary, are to be of the metal upon metal type or of an equivalent type.

3.2.4 Actuator oil seals between moving parts, forming part of the external pressure boundary, are to be such that the failure of one seal does not render the actuator inoperative.

3.2.5 Piping, joints, valves, flanges and other fittings are to comply within the requirements of Chapter 10 for Class I piping systems components. The design pressure is to be in accordance withPt 5, Ch 15, 3.1 General 3.1.6.

3.2.6 Hydraulic power operated steering gears are to be provided with arrangements to maintain the cleanliness of the hydraulic fluid taking into consideration the type and design of the hydraulic system.

3.3.1 For vessels with non-duplicated actuators, isolating valves are to be fitted at the connection of pipes to the actuator, and are to be directly fitted on the actuator.

3.3.2 Arrangements for bleeding air from the hydraulic system are to be provided, where necessary.

3.3.3 Relief valves are to be fitted to any part of the hydraulic system which can be isolated and in which pressure can be generated from the power source or from external forces. The settings of the relief valves are not to exceed the design pressure. The valves are to be of adequate size and so arranged as to avoid an undue rise in pressure above the design pressure.

3.3.4 Relief valves for protecting any part of the hydraulic system which can be isolated, as required by Pt 5, Ch 15, 3.3 Valve and relief valve arrangements 3.3.3, are to comply with the following:

1. The setting pressure is not to be less than 1,25 times the maximum working pressure.

2. The minimum discharge capacity of the relief valve(s) is not to be less than 110 per cent of the total capacity of the pumps which can deliver through it (them). Under such conditions the rise in pressure is not to exceed 10 per cent of the setting pressure. In this regard, due consideration is to be given to extreme foreseen ambient conditions in respect of oil viscosity.

3.4.1 Hose assemblies approved by Clasifications Register may be installed between two points where flexibility is required. In general, the hose should be limited to the length necessary to provide for flexibility and for proper operation of machinery, see Pt 5, Ch 10, 8 Hydraulic tests on pipes and fittings for the applicable requirements.

3.4.2 The service lifetime of the flexible hoses for the steering gear is not to exceed the Manufacturer’s recommendations. In all cases the hoses are to be replaced after 10 years of service.