Section
3 Construction and design
3.1 General
3.1.3 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.
3.1.4 The construction is to be such as to minimise local concentrations of
stress.
3.1.6 For the rudder actuator, the permissible primary general membrane stress
is not to exceed the lower of the following values:
where
![](svgobject/3139-4E09-8F57-EFFD359FD8CC.xml_d3424853e230.png) |
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specified minimum tensile strength of material at ambient
temperature |
![](svgobject/3139-4E09-8F57-EFFD359FD8CC.xml_d3424853e275.png) |
= |
specified minimum yield stress or 0,2 per cent proof stress of
the material at ambient temperature A and B are given by the
following Table:
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Wrought steel
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Cast steel
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Nodular cast iron
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A
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3,5
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4
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5
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B
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1,7
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2
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3
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3.2 Components
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, utilise 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 of at least the 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 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 duplicated, so that the failure of one seal does not
render the actuator inoperative. Alternative arrangements providing equivalent
protection against leakage may be accepted.
3.2.6 Hydraulic power-operated steering gears are to be provided with the
following:
- Arrangements to maintain the cleanliness of the hydraulic
fluid, taking into consideration the type and design of the hydraulic
system;
- A fixed storage tank having sufficient capacity to recharge at
least one power actuating system including the reservoir, where the main
steering gear is required to be power-operated. The storage tank is to be
permanently connected by piping, in such a manner that the hydraulic systems
can be readily recharged from a position within the steering gear
compartment and provided with a contents gauge.
3.3 Valve and relief valve
arrangements
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 where pressure can be generated from the power source or from
external forces. The settings of the relief valves is 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 19, 3.3 Valve and relief valve arrangements 3.3.3, are to comply with the following:
- The setting pressure is not to be less than 1,25 times the
maximum working pressure.
- 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 be
delivered through 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 Flexible hoses
3.4.1 Hose assemblies approved by LR may be installed between two points where
flexibility is required but are not to be subjected to torsional deflection
(twisting) under normal operating conditions. In general, the hose should be limited
to the length necessary to provide for flexibility and for proper operation of
machinery, see also
Pt 5, Ch 12 Piping Design Requirements
3.4.2 Hoses should be high pressure hydraulic hoses, according to recognised
standards and should be suitable for the fluids, pressures, temperatures and ambient
conditions in question.
3.4.3 Burst pressure of hoses is to be not less than four times the design
pressure.
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