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 The requirements
of this Chapter are based on the assumption of heavy traffic on relatively
narrow waterways through densely populated areas. When ships are intended
to be used on waterways with service conditions different from this,
they will receive special consideration.
1.1.3 Attention
is also drawn to additional requirements of National or International
Authorities, e.g. the Rules issued by the Central Rhine Commission.
1.1.4 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 wheel house 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 rudderstock (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 electro
hydraulic 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 maximum loaded draught, at maximum
propeller RPM and corresponding engine MCR.
1.2.7
Rudder
actuator means the components which converts directly hydraulic
pressure into mechanical action to move the rudder.
1.2.8
Maximum
working pressure means the maximum expected pressure in the
system when the steering gear is operated to comply with Pt 5, Ch 15, 2.1 General 2.1.2.
1.2.9
Steering
arrangements means the complete system of components for providing
ship directional control.
1.2.10
Directional
control systemmeans the equipment used to effect changes in
ship direction, e.g. the rudder, podded propulsion unit, azimuth thrusters
or water jet nozzle. Note that, for podded propulsion systems, azimuth
thrusters, water jet systems, or other similar systems for effecting
changes in ship direction, it is to be assumed that the units must
provide thrust in addition to rotation and hence the directional control
system must include the propulsion system.
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.
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
components used in steering arrangements for ship directional control
are to be manufactured in accordance with the Rules for Materials.
1.5.3 All steering
unit components transmitting mechanical forces are to be of steel
or other approved ductile material. 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 low pressure valve bodies
and mechanical 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
1.6.2 For the
requirements of tillers and quadrants including the tiller to stock
connection, see
Table 15.1.1 Connection of tiller to
stock.
Table 15.1.1 Connection of tiller to
stock
| Item
|
Requirements
|
| (1)
|
Dry fit – tiller to
stock,
see also
Pt 5, Ch 15, 1.6 Rudder, rudder stock, tiller and quadrant 1.6.5 and Pt 5, Ch 15, 1.6 Rudder, rudder stock, tiller and quadrant 1.6.6
|
(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 15, 1.6 Rudder, rudder stock, tiller and quadrant 1.6.5and Pt 5, Ch 15, 1.6 Rudder, rudder stock, tiller and quadrant 1.6.6
|
(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 15, 1.6 Rudder, rudder stock, tiller and quadrant 1.6.5
|
(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
|
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 = 0,0014δsu mm For 6 connecting bolts: t
s = 0,0012δsu mm
Key(s) to be
fitted
|
Diameter of bolts, 
|
A predetermined setting-up load equivalent to a stress of a
proximately 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
|
Effective sectional area of key in shear ≥ 0,25δsu
2 mm2
Key thickness ≥ 0,17δsu 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)
|
To be not less than the greater of:
|
| (a)
|
Z
TA = 
|
| (b)
|
Z
TA = 
|
| 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 4
|
| (7)
|
Boss
|
Depth of boss ≥ δsu mm
Thickness of
boss in way of tiller, irrespective of the keyway: ≥ 0,4δsu mm
|
| Symbols
|
|
b
s
|
= |
distance between the section of the tiller arm under
consideration and the centre of the rudder stock, in mm |
|
|
= |
NOTE: b
T and b
s are to be measured with zero rudder angle |
|
b
T
|
= |
distance from the point of application of the load on
the tiller to the centre of the rudder stock, in mm |
|
n
tb
|
= |
number of bolts in the connection flanges, but
generally not to be taken greater than six |
|
t
s
|
= |
thickness of shim for machining bolted tillers and
quadrants, in mm |
|
Z
TA
|
= |
section modulus of tiller arm, in cm3
|
|
|
= |
The rudderstock diameter obtained from Table 12.2.1 Rudder stock diameter in Pt 3, Ch 12 is based
on the specified material properties of the rudder stock. An
equivalent rudder stock diameter δe may be applied for
components having a different material from the rudder stock
material. This equivalent diameter may be determined as follows:-
|
where
|
|
= |
σo = the yield stress of the rudder stock
material |
|
|
= |
σoc = the yield stress of the component
material |
|
|
= |
Both stresses are to be taken not greater than 70 %
of the ultimate tensile strength or 450 N/mm2, whichever
is lesser. As a minimum, the stresses are to be not less than 200
N/mm2
|
|
d
tb
|
= |
diameter of bolts securing bolted tillers and
quadrants, in mm |
|
1.6.3 An efficient
locking or brake arrangement is to be fitted to all gears to keep
the rudder steady when necessary. In the case of hydraulic steering
gears which are fitted with isolating valves on the body of the gear
and duplicate power units, an additional mechanical brake need not
be fitted.
1.6.4 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.
1.6.5 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.
1.6.6 For conical
sections, S is based on the following equation:
|
S
|
= |
|
|
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, Q =
0,05)
|
|
μ |
= |
coefficient
of friction |
|
σr
|
= |
radial
interfacial pressure or grip stress, in N/mm2.
|
1.6.7 On double
rudder installations, where the two tillers are connected by mechanical
means (tie-bar), the strength and stability of the tie-bar is to be
assessed using the maximum steering torque applied to the stock.
1.6.8 Where
higher tensile steel bolts are used on bolted tillers and quadrants,
the yield and ultimate tensile stresses of the bolt material are to
be stated on plans submitted for approval, together with full details
of the methods to be adopted to obtain the required setting-up stress.
Where proprietary nuts or systems are used, the manufacturer's instructions
for assembly are to be adhered to.
|