Section
1 General
1.1 Application
1.1.1 Requirements for steering gear applicable to units designed to undertake
self-propelled passages without external assistance are given in Pt 5, Ch 19 Steering Systems of the Rules and Regulations for the
Classification of Ships (hereinafter referred to as the Rules for Ships),
which should be complied with in addition to the requirements in this Section.
1.1.2 When a ship unit is classed as a floating offshore installation at a
fixed location and the rudder is inoperative, see
Pt 4, Ch 10, 1 General
1.1.3 Where rudders are left in situ on ship units, positive locking
devices are to be fitted to steering gears to prevent rudders moving violently in
storm conditions. Plans, together with supporting design calculations, are to be
submitted for approval to show satisfactory capacity in the worst contemplated
environmental conditions.
1.1.4 Consideration of the predicted extreme wind and wave loadings, unit
orientation and wave headings, together with all other relevant environmental
conditions at the operating site, are to be taken into account in predicting forces
and moments on the rudder control systems.
1.1.5 In some circumstances, the positive locking devices required by Pt 5, Ch 19, 1.1 Application 1.1.3 may be omitted if it can be shown that, during
storm conditions, the existing (installed) hydraulic steering control system, either
temporarily power-operated or left with passive trapped hydraulic fluid in the
circuit but with relief valves open, is sufficient to counteract or dampen the
imposed rudder moments such as to control violent movements of the rudder. However,
in such cases, it may still prove necessary to carry out fatigue analysis of the
rudder to tiller and support arrangements, taking into account the expected
environmental sea wave velocity spectrums and structural natural frequencies to
ensure satisfactory fatigue lives.
1.1.6 With reference to Pt 5, Ch 19, 5.1 Electric power circuits 5.1.6, Pt 5, Ch 19, 5.2 Electric control circuits 5.2.2 and Pt 5, Ch 19, 6.1 General 6.1.2 of the Rules for Ships, see
also
Pt 6, Ch 2, 3.7 Alternative sources of emergency electrical power 3.7.9.
1.2 Definitions
1.2.1
Steering gear control system means the equipment by which orders are
transmitted from the navigating bridge to the steering gear power units. Steering
gear control systems comprise transmitters, receivers, hydraulic control pumps and
their associated motors, motor controllers, piping and cables.
1.2.2
Main steering gear means the machinery, rudder actuator(s), the steering gear
power units, if any, and ancillary equipment and the means of applying torque to the
rudder stock (e.g. tiller or quadrant) necessary for effecting movement of the
rudder for the purpose of steering the unit under normal service conditions.
1.2.3
Steering gear power unit means:
- in the case of electric steering gear, an electric motor and
its associated electrical equipment;
- in the case of electrohydraulic steering gear, an electric
motor and its associated electrical equipment and connected pump;
- in the case of other hydraulic steering gear, a driving engine
and connected pump.
1.2.4
Auxiliary steering gear means the equipment other than any part of the main
steering gear necessary to steer the unit in the event of failure of the main
steering gear but not including the tiller, quadrant or components serving the same
purpose.
1.2.5
Power actuating system means the hydraulic equipment provided for supplying
power to turn the rudder stock, comprising a steering gear power unit or units,
together with the associated pipes and fittings, and a rudder actuator. The power
actuating systems may share common mechanical components, i.e. tiller quadrant and
rudder stock, or components serving the same purpose.
1.2.6
Maximum ahead service speed means the maximum service speed which the unit is
designed to maintain, at the summer load waterline at maximum propeller RPM and
corresponding engine MCR.
1.2.7
Rudder actuator means the components which convert directly hydraulic
pressure into mechanical action to move the rudder.
1.3 General
1.3.1 The steering gear is to be secured to the seating by fitted bolts, and
suitable chocking arrangements are to be provided. The seating is to be of
substantial construction.
1.3.2 The steering gear compartment is to be:
- readily accessible and, as far as practicable, separated from
machinery spaces; and
- Provided with suitable arrangements to ensure working access to
steering gear machinery and controls. These arrangements are to include
handrails and gratings or other non-slip surfaces to ensure suitable working
conditions in the event of hydraulic fluid leakage.
1.4 Plans
1.4.1 Before starting construction, the steering gear machinery plans,
specifications and calculations are to be submitted. The plans are to give:
- Details of scantlings and materials of all load bearing and
torque transmitting components and hydraulic pressure-retaining parts
together with proposed rated torque and all relief valve settings.
- Schematic of the hydraulic system(s), together with pipe
material, relief valves and working pressures.
- Details of control and electrical aspects.
1.5 Materials
1.5.1 All the steering gear components and the rudder stock are to be of sound
reliable construction to the Surveyor’s satisfaction.
1.5.2 All components transmitting mechanical forces to the rudder stock are to
be tested according to the requirements of the Rules for the Manufacture, Testing
and Certification of Materials (hereinafter referred to as the Rules for
Materials).
1.5.3 Ram cylinders, pressure housings of rotary vane type actuators,
hydraulic power piping, valves, flanges and fittings, and all steering gear
components transmitting mechanical forces to the rudder stock (such as tillers,
quadrants, or similar components) are to be of steel or other approved ductile
material, duly tested in accordance with the requirements of the Rules for
Materials. In general, such material is to have an elongation of not less than 12
per cent and a tensile strength not in excess of 650 N/mm2. Special
consideration will be given to the acceptance of grey cast iron for valve bodies and
redundant parts with low stress levels.
1.5.4 Where appropriate, consideration will be given to the acceptance of
non-ferrous material.
1.6 Rudder, rudder stock, tiller and
quadrant
1.6.3 In bow rudders having a vertical locking pin operated from the deck
above, positive means are to be provided to ensure that the pin can be lowered only
when the rudder is exactly central. In addition, an indicator is to be fitted at the
deck to show when the rudder is exactly central.
1.6.4 The factor of safety against slippage, S (i.e. for torque
transmission by friction) is generally based on:
S = 
where
M. is the maximum torque at the relief valve pressure which is
generally equal to the design torque as specified by the steering gear
manufacturer.
1.6.5 For conical sections, S is based on the following equation:
S = 
where
|
A |
= |
interfacial surface area, in mm2
|
|
W |
= |
weight of rudder and stock, if applicable, when tending to
separate the fit, in N |
|
Q |
= |
shear force =  in N |
where
 is the mean contact diameter of tiller/stock interface and
M in Nmm is defined in Pt 5, Ch 19, 1.6 Rudder, rudder stock, tiller and quadrant 1.6.4, in mm
|
θ |
= |
cone taper half angle in radians (e.g. for cone taper 1:10, θ
= 0,05) |
|
μ |
= |
coefficient of friction |
 |
= |
radial interfacial pressure or grip stress, in
N/mm2. |
Table 19.1.1 Connection of tiller to
stock
| Item
|
Requirements
|
|
(1) Dry fit – tiller to stock,
see also
Pt 5, Ch 19, 1.6 Rudder, rudder stock, tiller and quadrant 1.6.4 and Pt 5, Ch 19, 1.6 Rudder, rudder stock, tiller and quadrant 1.6.5
|
(a) For keyed connection, factor of safety against
slippage, S = 1,0
The maximum stress in the fillet radius of the
tiller keyway should not exceed the yield stress
For conical sections, the cone taper should be ≤
1:10
|
|
(b) For keyless connection, factor of safety against
slippage, S = 2,0
The maximum equivalent Von Mises stress should not
exceed the yield stress
For conical sections, the cone taper should be ≤
1:15
|
| (c) Coefficient of friction (maximum) = 0,17
|
| (d) Grip
stress not to be less than 20 N/mm2
|
|
(2) Hydraulic fit – tiller to stock,
see also
Pt 5, Ch 19, 1.6 Rudder, rudder stock, tiller and quadrant 1.6.4 and Pt 5, Ch 19, 1.6 Rudder, rudder stock, tiller and quadrant 1.6.5
|
(a) For keyed connection, factor of safety against
slippage, S = 1,0
The maximum stress in the fillet radius of the
tiller keyway should not exceed the yield stress
For conical sections, the cone taper should be ≤ 1:10
|
|
(b) For keyless connection, factor of safety against
slippage, S = 2,0
The maximum equivalent Von Mises stress should not
exceed the yield stress
For conical sections, the cone taper should be ≤
1:15
|
| (c)
Coefficient of friction (maximum) = 0,14
|
| (d) Grip
stress not to be less than 20 N/mm2
|
|
(3) Ring locking assemblies fit – tiller to
stock,
see also
Pt 5, Ch 19, 1.6 Rudder, rudder stock, tiller and quadrant 1.6.3
|
(a) Factor of safety against slippage, S =
2,0
The maximum equivalent Von Mises stress should not
exceed the yield stress
|
| (b)
Coefficient of friction = 0,12
|
| (c) Grip
stress not to be less than 20 N/mm2
|
|
(4) Bolted tiller and quadrant
(this arrangement could be accepted provided
theproposed rudder stock diameter in way of tillerdoes not
exceed 350 mm diameter), see symbols
|
Shim to be fitted between two halves before machining to take
rudder stock, then removed prior to fitting
|
| Minimum thickness of shim,
|
For 4 connecting bolts:  = 0,0014  mm
|
For 6 connecting bolts:  = 0,0012  mm
|
| Key(s) to be fitted
|
Diameter of bolts, 
|
| A
predetermined setting-up load equivalent to a stress of
approximately 0,7 of the yield strength of the bolt material should
be applied to each bolt on assembly. A lower stress may be accepted
provided that two keys, complying with item (5), are fitted
|
Distance from centre of stock to centre of bolts should generally
be equal to 
|
Thickness of
flange on each half of the bolted tiller ≥ 
|
|
(5) Key/keyway,
see symbols
|
Effective sectional area of key in shear ≥ 0,25  mm2
|
Key thickness ≥ 0,17  mm
|
| Keyway is to
extend over full depth of tiller and is to have a rounded end.
Keyway root fillets are to be provided with suitable radii to avoid
high local stress
|
|
(6) Section modulus – tiller arm
(at any point within its length about vertical
axis),
see symbols
|
To
be not less than the greater of:
|
(a) 
|
(b) 
|
| If more than one arm fitted, combined modulus is to be not less
than the greater of (a) or (b)
|
| For solid
tillers, the breadth to depth ratio is not to exceed 2
|
|
(7) Boss,
see symbols
|
Depth of boss ≥ 
Thickness of boss in way of tiller ≥ 0,4 
|
| Symbols
|
 = distance between the section of the tiller arm
under consideration and the centre of the rudder stock, in mm
|
 = thickness of shim for machining bolted tillers
and quadrants, in mm
|
NOTE:  and  are to be measured with zero rudder angle
|
 = section modulus of tiller arm, in
cm3
|
 = distance from the point of application of the
load on the tiller to the centre of the rudder stock, in mm
|
 = Rule rudderstock diameter in way of tiller,
see
Pt 3, Ch 13 Ship Control Systems of the Rules for Ships
|
 = number of bolts in the connection flanges, but
generally not to be taken greater than six
|
 = diameter of bolts securing bolted tillers and
quadrants, in mm
|
|