Section
1 General
1.1 Application
1.1.1 The requirements of this Chapter apply to the design and construction of
steering systems.
1.1.2 Whilst
the requirements satisfy the relevant regulations of the
SOLAS - International Convention for the Safety of Life at Sea
as amended, and the IMO Protocol of 1978, attention
should be given to any relevant statutory requirements of the National
Authority of the country in which the ship is to be registered.
1.1.3 Consideration
will be given to other cases, or to arrangements which are equivalent
to those required by the Rules.
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 ship 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 ship 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
ship 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.
1.2.9 Steering system means a complete system of sub-systems and equipment capable of
steering the ship including: the rudder (or podded propulsion unit, azimuth thruster,
steerable water jet as applicable), main steering gear, auxiliary steering gear and
steering gear control system.
1.2.10 Declared steering angle limits are the operational limits in terms
of maximum steering angle, or equivalent, according to manufacturer’s guidelines for
safe operation, also taking into account the ship's speed or propeller torque/speed or
other limitation. Trials to determine the ship's manoeuvring characteristics are to be
carried out with steering angles not exceeding the declared steering angle limits.
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 components used in the steering system are to be of sound reliable
construction to the Surveyor’s satisfaction.
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 the Manufacture, Testing and Certification of Materials, July 2022.
In general, such material is to have an elongation of not less than
12 per cent nor a tensile strength 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
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:
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 |
|
θ |
= |
cone taper
half angle in radians (e.g. for cone taper 1:10, θ = 0,05) |
|
μ |
= |
coefficient
of friction |
|
σr
|
= |
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) or 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 the proposed rudder
stock diameter in way of tiller does 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: t
s = 0,0014 δt mm
For 6 connecting
bolts: t
s = 0,0012 δt 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 δt
2 mm2
|
| Key thickness ≥ 0,17 δt 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:
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 ≥
δt
Thickness of boss in way of tiller ≥ 0,4 δt
|
| Symbols
|
|
bs
|
= |
distance between the section of the tiller arm under
consideration and the centre of the rudder stock, in mm |
|
| bT and bs are to
be measured with zero rudder angle
|
|
bT
|
= |
distance from the point of application of the load on
the tiller to the centre of the rudder stock, in mm |
|
|
ntb
|
= |
number of bolts in the connection flanges, but
generally not to be taken greater than six |
|
|
ts
|
= |
thickness of shim for machining bolted tillers and
quadrants, in mm |
|
|
ZTA
|
= |
section modulus of tiller arm, in cm3
|
|
|
|
|
δtb
|
= |
diameter of bolts securing bolted tillers and
quadrants, in mm |
|
|