Pt C, Ch 1, Sec 11

SECTION 11 STEERING GEAR

1 General • Ch 1, Sec 15, as regards sea trials

• Pt B, Ch 10, Sec 1, as regards the rudder and the rudder
1.1 Application stock
• Pt D, Ch 7, Sec 4, [7], when fitted to oil tankers, chemi-
1.1.1 Scope cal tankers or gas carriers.
Unless otherwise specified, the requirements of this Section
apply to the steering gear systems of all mechanically pro- 1.2 Documentation to be submitted
pelled ships, and to the steering mechanism of thrusters
used as means of propulsion. 1.2.1 Documents to be submitted for all steering
gear
1.1.2 Cross references Before starting construction, all plans and specifications
In addition to the those provided in this Section, steering listed in Tab 1 are to be submitted to the Society for
gear systems are also to comply with the requirements of: approval.

Table 1: Documents to be submitted for steering gear

Item Status of the

Description of the document (1)
No review (2)
1 I Assembly drawing of the steering gear including sliding blocks, guides, stops and other similar components
2 I General description of the installation and of its functioning principle
3 I Operating manuals of the steering gear and of its main components
4 I Description of the operational modes intended for steering in normal and emergency conditions
5 A For hydraulic steering gear, the schematic layout of the hydraulic piping of power actuating systems,
including the hydraulic fluid refilling system, with indication of:
• the design pressure
• the maximum working pressure expected in service
• the diameter, thickness, material specification and connection details of the pipes
• the hydraulic fluid tank capacity
• the flashpoint of the hydraulic fluid
6 I For hydraulic pumps of power units, the assembly longitudinal and transverse sectional drawings and the
characteristic curves
7 A Assembly drawings of the rudder actuators and constructional drawings of their components, with, for
hydraulic actuators, indication of:
• the design torque
• the maximum working pressure
• the relief valve setting pressure
8 I Constructional drawings of the relief valves for protection of the hydraulic actuators, with indication of:
• the setting pressure
• the relieving capacity
9 A Diagrams of the electric power circuits
10 A Functional diagram of control, monitoring and safety systems including the remote control from the
navigating bridge, with indication of the location of control, monitoring and safety devices
11 A Constructional drawings of the strength parts providing a mechanical transmission of forces to the rudder
stock (tiller, quadrant, connecting rods and other similar items), with the calculation notes of the shrink-fit
connections
12 I/A For azimuth thrusters used as steering means, the specification and drawings of the steering mechanism and,
where applicable, documents 2 to 6 and 8 to 11 above
(1) Constructional drawings are to be accompanied by the specification of the materials employed and, where applicable, by the
welding details and welding procedures.
(2) Submission of the drawings may be requested :
for approval, shown as “A”; for information, shown as “I”.

April 2007 Bureau Veritas 207

Pt C, Ch 1, Sec 11

1.2.2 Additional documents 1.3.7 Maximum ahead service speed

The following additional documents are to be submitted: Maximum ahead service speed is the greatest speed which
• analysis in relation to the risk of single failure, where the ship is designed to maintain in service at sea at the
required by [3.5.2] deepest seagoing draught.
• analysis in relation to the risk of hydraulic locking, 1.3.8 Maximum astern speed
where required by [3.5.5]
Maximum astern speed is the speed which it is estimated
• failure analysis in relation to the availability of the the ship can attain at the designed maximum astern power
hydraulic power supply, where required by [4.5.3], item at the deepest seagoing draught.
b)
• fatigue analysis and/or fracture mechanics analysis, 1.3.9 Maximum working pressure
where required by Pt D, Ch 7, Sec 4, [7.2.1] and Pt D, Maximum working pressure is the maximum expected pres-
Ch 7, Sec 4, [7.3.1]. sure in the system when the steering gear is operated to
comply with the provisions of [3.3.1] item b) or [4.3.1] item
1.3 Definitions b).

1.3.1 Main steering gear 1.4 Symbols

Main steering gear is the machinery, rudder actuators, steer-
ing gear power units, if any, and ancillary equipment and 1.4.1 The following symbols are used for strength criteria of
the means of applying torque to the rudder stock (e.g. tiller steering gear components:
or quadrant) necessary for effecting movement of the rud- V : Maximum service speed, in knots, with the ship
der for the purpose of steering the ship under normal serv- on summer load waterline. When the speed is
ice conditions. less than 10 knots, V is to be replaced by the
value (V+20)/3
1.3.2 Steering gear power unit ds : Rule diameter of the rudder stock in way of the
Steering gear power unit is: tiller, in mm, defined in Pt B, Ch 10, Sec 1, [4]
• in the case of electric steering gear, an electric motor and calculated with a material factor k1 = 1
and its associated electrical equipment dse : Actual diameter of the upper part of the rudder
• in the case of electrohydraulic steering gear, an electric stock in way of the tiller, in mm
motor and its associated electrical equipment and con- (in the case of a tapered coupling, this diameter
nected pump is measured at the base of the assembly)
• in the case of other hydraulic steering gear, a driving TR : Rule design torque of the rudder stock given, in
engine and connected pump. kN.m, by the following formula:
T R = 13 ,5 ⋅ d s ⋅ 10
3 –6
1.3.3 Auxiliary steering gear
Auxiliary steering gear is the equipment other than any part TE : For hand emergency operation, design torque
of the main steering gear necessary to steer the ship in the due to forces induced by the rudder, in kN.m,
event of failure of the main steering gear but not including given by the following formulae:
the tiller, quadrant or components serving the same pur-
pose. V E + 2 2
T E = 0 ,62 ⋅  --------------- ⋅ TR
 V +2
1.3.4 Power actuating system
where:
Power actuating system is the hydraulic equipment pro-
• VE = 7 where V ≤ 14
vided for supplying power to turn the rudder stock, com-
prising a steering gear power unit or units, together with the • VE = 0,5 V where V > 14
associated pipes and fittings, and a rudder actuator. The TG : For main hydraulic or electrohydraulic steering
power actuating systems may share common mechanical gear, torque induced by the main steering gear
components, i.e. tiller, quadrant and rudder stock, or com- on the rudder stock when the pressure is equal
ponents serving the same purpose. to the setting pressure of the relief valves pro-
tecting the rudder actuators
1.3.5 Rudder actuator
Note 1: for hand-operated main steering gear, the following
Rudder actuator is the component which directly converts value is to be used:
hydraulic pressure into mechanical action to move the rud-
TG = 1,25.TR
der.
TA : For auxiliary hydraulic or electrohydraulic steer-
1.3.6 Steering gear control system ing geas, torque induced by the auxiliary steer-
Steering gear control system is the equipment by which ing gear on the rudder stock when the pressure
orders are transmitted from the navigation bridge to the is equal to the setting pressure of the relief
steering gear power units. Steering gear control systems valves protecting the rudder actuators
comprise transmitters, receivers, hydraulic control pumps Note 2: for hand-operated auxiliary steering gear, the follow-
and their associated motors, motor controllers, piping and ing value is to be used:
cables. TA = 1,25.TE

208 Bureau Veritas April 2007

 Pt C, Ch 1, Sec 11

T’G : For steering gear which can activate the rudder to be permanently lubricated or provided with lubrica-
with a reduced number of actuators, the value tion fittings.
of TG in such conditions c) The construction is to be such as to minimise local con-
σ : Normal stress due to the bending moments and centration of stress.
the tensile and compressive forces, in N/mm2 d) All steering gear components transmitting mechanical
τ : Tangential stress due to the torsional moment forces to the rudder stock, which are not protected
and the shear forces, in N/mm2 against overload by structural rudder stops or mechani-
σa : Permissible stress, in N/mm2 cal buffers, are to have a strength at least equivalent to
that of the rudder stock in way of the tiller.
σc : Combined stress, determined by the following
formula: 2.1.2 Materials and welds

σc =
2
σ + 3τ
2 a) All steering gear components transmitting mechanical
forces to the rudder stock (such as tillers, quadrants, or
R : Value of the minimum specified tensile strength similar components) are to be of steel or other approved
of the material at ambient temperature, in ductile material complying with the requirements of
N/mm2 NR216 Materials and Welding. In general, such material
Re : Value of the minimum specified yield strength is to have an elongation of not less than 12% and a ten-
of the material at ambient temperature, in sile strength not greater than 650 N/mm2.
N/mm2 b) The use of grey cast iron is not permitted, except for
R’e : Design yield strength, in N/mm2, determined by redundant parts with low stress level, subject to special
the following formulae: consideration by the Society. It is not permitted for cyl-
inders.
• R’e = Re, where R ≥ 1,4 Re
c) The welding details and welding procedures are to be
• R’e = 0,417 (Re + R) where R < 1,4 Re
submitted for approval.
d) All welded joints within the pressure boundary of a rud-
2 Design and construction - der actuator or connecting parts transmitting mechani-
Requirements applicable to all ships cal loads are to be full penetration type or of equivalent
strength.
2.1 Mechanical components
2.1.3 Scantling of components
2.1.1 General The scantling of steering gear components is to be deter-
a) All steering gear components and the rudder stock are mined considering the design torque MT and the permissi-
to be of sound and reliable construction to the satisfac- ble value σa of the combined stress, as given in:
tion of the Society. • Tab 2 for components which are protected against over-
b) Any non-duplicated essential component is, where loads induced by the rudder
appropriate, to utilise anti-friction bearings, such as ball • Tab 3 for components which are not protected against
bearings, roller bearings or sleeve bearings, which are overloads induced by the rudder.

Table 2: Scantling of components protected against overloads induced by the rudder

Conditions of use of the components MT σa

Normal operation TG • if TG ≤ 1,25 TR : σa = 1,25 σ0
• if 1,25 TR < TG < 1,50 TR : σa = σ0 TG/TR
• if TG ≥ 1,50 TR : σa = 1,50 σ0
where σ0 = 0,55 R’e
Normal operation, with a reduced number of T’G • if T’G ≤ 1,25 TR : σa = 1,25 σ0
actuators • if 1,25 TR < T’G < 1,50 TR : σa = σ0 TG/TR
• if T’G ≥ 1,50 TR : σa = 1,50 σ0
where σ0 = 0,55 R’e
Emergency operation achieved by hydraulic or lower of TR and 0,8 TA 0,69 R’e
electrohydraulic steering gear
Emergency operation, with a reduced number lower of TR and 0,8 T’G 0,69 R’e
of actuators
Emergency operation achieved by hand TE 0,69 R’e

April 2007 Bureau Veritas 209

Pt C, Ch 1, Sec 11

Table 3: Scantling of components not protected against overloads induced by the rudder

Conditions of use of the components MT σa

Normal operation TR 0,55 R’e
Normal operation, with a reduced number of actuators lower of TR and 0,8 T’G 0,55 R’e
Emergency operation achieved by hydraulic or electrohydraulic steering gear lower of TR and 0,8 TA 0,69 R’e
Emergency operation, with a reduced number of actuators lower of TR and 0,8 T’G 0,69 R’e
Emergency operation achieved by hand TE 0,69 R’e

2.1.4 Tillers, quadrants and rotors b) The scantling of the quadrants is to be determined as
a) The scantling of the tiller is to be determined as follows: specified in a) for the tillers. When quadrants having
two or three arms are provided, the section modulus of
• the depth H0 of the boss is not to be less than 0,75.ds
each arm is not to be less than one half or one third,
• the radial thickness of the boss in way of the tiller is respectively, of the section modulus required for the
not to be less than the greater of: tiller.

• 235
0, 3 ⋅ d s ⋅ ---------- Arms of loose quadrants not keyed to the rudder stock
R′ e may be of reduced dimensions to the satisfaction of the
Society, and the depth of the boss may be reduced by
• 0, 25 ⋅ d s
10 per cent.
c) Keys are to satisfy the following provisions:
• the section modulus of the tiller arm in way of the
end fixed to the boss is not to be less than the value • the key is to be made of steel with a yield stress not
Zb, in cm3, calculated from the following formula: less than that of the rudder stock and that of the tiller
boss or rotor without being less than 235 N/mm2
0 ,147 ⋅ d L ′ R
3

Z b = -------------------------s ⋅ ---- ⋅ -----e′ • the width of the key is not to be less than 0,25.ds
1000 L Re
• the thickness of the key is not to be less than 0,10.ds
where:
L : Distance from the centreline of the rud- • the ends of the keyways in the rudder stock and in
der stock to the point of application of the tiller (or rotor) are to be rounded and the keyway
the load on the tiller (see Fig 1) root fillets are to be provided with small radii of not
less than 5 per cent of the key thickness.
L’ : Distance between the point of applica-
tion of the above load and the root sec- d) Bolted tillers and quadrants are to satisfy the following
tion of the tiller arm under consideration provisions:
(see Fig 1) • the diameter of the bolts is not to be less than the
• the width and thickness of the tiller arm in way of value db, in mm, calculated from the following for-
the point of application of the load are not to be less mula:
than one half of those required by the above formula
TR 235
• in the case of double arm tillers, the section modu- - ⋅ ----------
d b = 153 ---------------------------------
n ( b + 0 ,5d s e ) R e b
lus of each arm is not to be less than one half of the
section modulus required by the above formula. where:
n : Number of bolts located on the same
Figure 1: Tiller arm
side in respect of the stock axis (n is not
to be less than 2)
b : Distance between bolts and stock axis,
in mm (see Fig 2)
Reb : Yield stress, in N/mm2, of the bolt mate-
L'

rial
L

• the thickness of each of the tightening flanges of the

two parts of the tiller is not to be less than the fol-
lowing value:

n ⋅ ( b – 0, 5 ⋅ D e ) R e b
1, 85 ⋅ d b ⋅ ------------------------------------------ ⋅ -------
′
H0 Re
Where:
De : External boss diameter, in mm (average
H0
value)

210 Bureau Veritas April 2007

 Pt C, Ch 1, Sec 11

• in order to ensure the efficient tightening of the cou- b) in respect of the buckling strength:
pling around the stock, the two parts of the tiller are
4 -  8M
to bored together with a shim having a thickness not ----------- ⋅ ωF c + --------- ≤ 0 ,9σ a
π D2  D2 
2
less than the value j, in mm, calculated from the fol-
lowing formula: where:
j = 0,0015 ⋅ ds D2 : Piston rod diameter, in mm
Fc : Compression force in the rod, in N, when it
Figure 2: Bolted tillers
extends to its maximum stroke
M : Possible bending moment in the piston rod,
n bolts db
in N.mm, in way of the fore end of the cyl-
inder rod bearing
ω : ω = β + (β2 − α)0,5
d se with:
α = 0,0072 (ls D 2)2 . R’e/235
β = 0,48 + 0,5 α + 0,1 α0,5
ls = Length, in mm, of the maximum unsup-
ported reach of the cylinder rod.

2.2 Hydraulic system

b
2.2.1 General

e) Shrink-fit connections of tiller (or rotor) to stock are to a) The design pressure for calculations to determine the
satisfy the following provisions: scantlings of piping and other steering gear components
subjected to internal hydraulic pressure shall be at least
• the safety factor against slippage is not to be less 1,25 times the maximum working pressure to be
than: expected under the operational conditions specified in
• 1 for keyed connections [3] and [4], taking into account any pressure which may
exist in the low pressure side of the system.
• 2 for keyless connections
At the discretion of the Society, high cycle and cumula-
• the friction coefficient is to be taken equal to:
tive fatigue analysis may be required for the design of
• 0,15 for steel and 0,13 for spheroidal graphite piping and components, taking into account pulsating
cast iron, in the case of hydraulic fit pressures due to dynamic loads.
• 0,17 in the case of dry shrink fitting b) The power piping for hydraulic steering gear is to be
• the combined stress according to the von Mises cri- arranged so that transfer between units can be readily
terion, due to the maximum pressure induced by the effected.
shrink fitting and calculated in way of the most c) Arrangements for bleeding air from the hydraulic system
stressed points of the shrunk parts, is not to exceed are to be provided, where necessary.
80 per cent of the yield stress of the material consid-
ered d) The hydraulic piping system, including joints, valves,
flanges and other fittings, is to comply with the require-
Note 1: Alternative stress values based on FEM calculations may ments of Ch 1, Sec 10 for class I piping systems, and in
also be considered by the Society. particular with the requirements of Ch 1, Sec 10, [14],
• the entrance edge of the tiller bore and that of the unless otherwise stated.
rudder stock cone are to be rounded or bevelled.
2.2.2 Materials
2.1.5 Piston rods a) Ram cylinders, pressure housings of rotary vane type
The scantling of the piston rod is to be determined taking actuators, hydraulic power piping, valves, flanges and
into account the bending moments, if any, in addition to fittings are to be of steel or other approved ductile mate-
compressive or traction forces and is to satisfy the following rial.
provisions:
b) In general, such material is to have an elongation of not
a) σc ≤ σa less than 12% and a tensile strength not greater than
650 N/mm2.
where:
Grey cast iron may be accepted for valve bodies and
σc : Combined stress as per [1.4.1]
redundant parts with low stress level, excluding cylin-
σa : Permissible stress as per [2.1.3] ders, subject to special consideration.

April 2007 Bureau Veritas 211

Pt C, Ch 1, Sec 11

2.2.3 Isolating valves Note 1: For cargo ships of less than 500 tons gross tonnage and for
Shut-off valves, non-return valves or other appropriate fishing vessels, the storage means may consist of a readily accessi-
ble drum, of sufficient capacity to refill one power actuating system
devices are to be provided:
if necessary.
• to comply with the availability requirements of [3.5] or
[4.5] 2.2.7 Hydraulic pumps
• to keep the rudder steady in position in case of emer-
a) Hydraulic pumps are to be type tested in accordance
gency.
with the provisions of [8.1.1].
In particular, for all ships with non-duplicated actuators,
b) Special care is to be given to the alignment of the pump
isolating valves are to be fitted at the connection of pipes to
and the driving motor.
the actuator, and are to be directly fitted on the actuator.

2.2.4 Flexible hoses 2.2.8 Filters

a) Flexible hoses may be installed between two points a) Hydraulic power-operated steering gear shall be pro-
where flexibility is required but are not to be subjected vided with arrangements to maintain the cleanliness of
to torsional deflexion (twisting) under normal operation. the hydraulic fluid taking into consideration the type
In general, the hose is to be limited to the length neces- and design of the hydraulic system.
sary to provide for flexibility and for proper operation of
b) Filters of appropriate mesh fineness are to be provided
machinery.
in the piping system, in particular to ensure the protec-
b) Hoses are to be high pressure hydraulic hoses according tion of the pumps.
to recognised standards and suitable for the fluids, pres-
sures, temperatures and ambient conditions in question. 2.2.9 Accumulators
c) They are to be of a type approved by the Society. Accumulators, if fitted, are to be designed in accordance
d) The burst pressure of hoses is to be not less than four with Ch 1, Sec 10, [14.5.3].
times the design pressure.
2.2.10 Rudder actuators
2.2.5 Relief valves
a) Rudder actuators, other than non-duplicated rudder
a) Relief valves shall be fitted to any part of the hydraulic actuators fitted to tankers, chemical carriers and gas car-
system which can be isolated and in which pressure can riers of 10000 gross tonnage and above, are to be
be generated from the power source or from external designed in accordance with the relevant requirements
forces. The setting of the relief valves shall not exceed of Ch 1, Sec 3 for class 1 pressure vessels also consider-
the design pressure. The valves shall be of adequate size ing the following provisions.
and so arranged as to avoid an undue rise in pressure
above the design pressure. b) The permissible primary general membrane stress is not
to exceed the lower of the following values:
b) The setting pressure of the relief valves is not to be less
than 1,25 times the maximum working pressure. R- Re
--- or -----
c) The minimum discharge capacity of the relief valve(s) is A B
not to be less than the total capacity of the pumps which where A and B are given in Tab 4.
can deliver through it (them), increased by 10%. Under
such conditions, the rise in pressure is not to exceed c) Oil seals between non-moving parts, forming part of the
10% of the setting pressure. In this respect, due consid- external pressure boundary, are to be of the metal upon
eration is to be given to the foreseen extreme ambient metal or equivalent type.
conditions in relation to oil viscosity.
d) Oil seals between moving parts, forming part of the
2.2.6 Hydraulic oil reservoirs external pressure boundary, are to be duplicated, so that
the failure of one seal does not render the actuator inop-
Hydraulic power-operated steering gear shall be provided
erative. Alternative arrangements providing equivalent
with the following:
protection against leakage may be accepted.
• a low level alarm for each hydraulic fluid reservoir to
give the earliest practicable indication of hydraulic fluid e) The strength and connection of the cylinder heads (or,
leakage. Audible and visual alarms shall be given on the in the case of actuators of the rotary type, the fixed
navigation bridge and in the machinery space where vanes) acting as rudder stops are to comply with the
they can be readily observed. provisions of [7.3.1].
• a fixed storage tank having sufficient capacity to
recharge at least one power actuating system including Table 4: Value of coefficients A and B
the reservoir, where the main steering gear is required to
be power operated. The storage tank shall be perma- Nodular cast
Coefficient Steel Cast steel
nently connected by piping in such a manner that the iron
hydraulic systems can be readily recharged from a posi-
A 3,5 4 5
tion within the steering gear compartment and shall be
provided with a contents gauge. B 1,7 2 3

212 Bureau Veritas April 2007

 Pt C, Ch 1, Sec 11

2.3 Electrical systems b) Motors for steering gear power units may be rated for
intermittent power demand.
2.3.1 General design The rating is to be determined on the basis of the steer-
The electrical systems of the main steering gear and the ing gear characteristics of the ship in question; the rating
auxiliary steering gear are to be so arranged that the failure is always to be at least:
of one will not render the other inoperative. • S3 - 40% for motors of electric steering gear power
units
2.3.2 Power circuit supply
• S6 - 25% for motors of electrohydraulic steering
a) Electric or electrohydraulic steering gear comprising gear power units and for convertors.
one or more power units is to be served by at least two c) Each electric motor of a main or auxiliary steering gear
exclusive circuits fed directly from the main switch- power unit is to be provided with its own separate
board; however, one of the circuits may be supplied motor starter gear, located within the steering gear com-
through the emergency switchboard. partment.
b) Auxiliary electric or electrohydraulic steering gear,
associated with main electric or electrohydraulic steer- 2.3.4 Supply of motor control circuits and steering
gear control systems
ing gear, may be connected to one of the circuits sup-
plying the main steering gear. a) Each control for starting and stopping of motors for
power units is to be served by its own control circuits
c) The circuits supplying electric or electrohydraulic steer- supplied from its respective power circuits.
ing gear are to have adequate rating for supplying all
motors which can be simultaneously connected to them b) Any electrical main and auxiliary steering gear control
and may be required to operate simultaneously. system operable from the navigating bridge is to be
served by its own separate circuit supplied from a steer-
d) When, in a ship of less than 1600 tons gross tonnage, ing gear power circuit from a point within the steering
auxiliary steering gear which is required by [3.3.2], item gear compartment, or directly from switchboard busbars
c) to be operated by power is not electrically powered supplying that steering gear power circuit at a point on
or is powered by an electric motor primarily intended the switchboard adjacent to the supply to the steering
for other services, the main steering gear may be fed by gear power circuit. The power supply systems are to be
one circuit from the main switchboard. protected selectively.
e) Where the rudder stock is required to be over 230 milli- c) The remote control of the power unit and the steering
metres in diameter in way of the tiller, excluding gear control systems is to be supplied also by the alter-
strengthening for navigation in ice, an alternative power native power source when required by [2.3.2], item e).
supply either from the emergency source of electrical
power or from an independent source of power located 2.3.5 Circuit protection
in the steering gear compartment is to be provided, suf-
a) Short-circuit protection is to be provided for each con-
ficient at least to supply the steering gear power unit
trol circuit and each power circuit of electric or electro-
such that the latter is able to perform the duties of auxil-
hydraulic main and auxiliary steering gear.
iary steering gear.
b) No protection other than short-circuit protection is to be
This power source is to be activated automatically, provided for steering gear control system supply cir-
within 45 seconds, in the event of failure of the main cuits.
source(s) of electrical power.
c) Protection against excess current (e.g. by thermal
The independent source is to be used only for this pur- relays), including starting current, if provided for power
pose. circuits, is to be for not less than twice the full load cur-
The alternative power source is also to supply the steer- rent of the motor or circuit so protected, and is to be
ing gear control system, the remote control of the power arranged to permit the passage of the appropriate start-
unit and the rudder angle indicator. ing currents.
d) Steering gear motor circuits obtaining their power sup-
f) In every ship of 10 000 tons gross tonnage and upwards,
ply via an electronic converter, e.g. for speed control,
the alternative power supply is to have a capacity for at
and which are limited to full load current are exempt
least 30 minutes of continuous operation and in any
from the requirement to provide protection against
other ship for at least 10 minutes.
excess current, including starting current, of not less
than twice the full load current of the motor. The
2.3.3 Motors and associated control gear
required overload alarm is to be set to a value not
a) To determine the required characteristics of the electric greater than the normal load of the electronic converter.
motors for power units, the breakaway torque and max- Note 1:“Normal load” is the load in normal mode of operation that
imum working torque of the steering gear under all approximates as close as possible to the most severe conditions
operating conditions are to be considered. The ratio of of normal use in accordance with the manufacturer’s operating
pull-out torque to rated torque is to be at least 1,6. instructions.

April 2007 Bureau Veritas 213

Pt C, Ch 1, Sec 11

e) Where fuses are fitted, their current ratings are to be two control and follow-up control, it is to be ensured that
step higher than the rated current of the motors. How- the follow-up amplifier is protected selectively.
ever, in the case of intermittent service motors, the fuse i) Control circuits for additional control systems, e.g.
rating is not to exceed 160% of the rated motor current. steering lever or autopilot, are to be designed for all-
f) The instantaneous short-circuit trip of circuit breakers is pole disconnection.
to be set to a value not greater than 15 times the rated j) The feedback units and limit switches, if any, for the
current of the drive motor. steering gear control systems are to be separated electri-
g) The protection of control circuits is to correspond to at cally and mechanically connected to the rudder stock or
least twice the maximum rated current of the circuit, actuator separately.
though not, if possible, below 6 A. k) Actuators controlling the power systems of the steering
gear, e.g. magnetic valves, are to be duplicated and sep-
2.3.6 Starting and stopping of motors for steering arated.
gear power units
a) Motors for power units are to be capable of being 2.4 Alarms and indications
started and stopped from a position on the navigation
bridge and from a point within the steering gear com- 2.4.1 Power units
partment. a) In the event of a power failure to any one of the steering
b) Means are to be provided at the position of motor start- gear power units, an audible and visual alarm shall be
ers for isolating any remote control starting and stopping given on the navigating bridge.
devices (e.g. by removal of the fuse-links or switching b) Means for indicating that the motors of electric and elec-
off the automatic circuit breakers). trohydraulic steering gear are running shall be installed
c) Main and auxiliary steering gear power units are to be on the navigating bridge and at a suitable main machin-
arranged to restart automatically when power is restored ery control position.
after a power failure. c) Where a three-phase supply is used, an alarm shall be
provided that will indicate failure of any one of the sup-
2.3.7 Separation ply phases.
a) Duplicated electric power circuits are to be separated as d) An overload alarm shall be provided for each motor of
far as practicable. electric or electrohydraulic steering gear power units.
b) Cables for duplicated electric power circuits with their e) The alarms required in c) and d) shall be both audible
associated components are to be separated as far as and visual and situated in a conspicuous position in the
practicable. They are to follow different routes separated main machinery space or control room from which the
both vertically and horizontally, as far as practicable, main machinery is normally controlled.
throughout their entire length.
2.4.2 Hydraulic system
c) Duplicated steering gear control systems with their asso-
ciated components are to be separated as far as practi- a) Hydraulic oil reservoirs are to be provided with the
cable. alarms required in [2.2.6].
b) Where hydraulic locking, caused by a single failure,
d) Cables for duplicated steering gear control systems with
may lead to loss of steering, an audible and visual
their associated components are to be separated as far
alarm, which identifies the failed system, is to be pro-
as practicable. They are to follow different routes sepa-
vided on the navigating bridge.
rated both vertically and horizontally, as far as practica-
Note 1: This alarm is to be activated when, for example:
ble, throughout their entire length.
• the position of the variable displacement pump control
e) Wires, terminals and the components for duplicated system does not correspond with the given order, or
steering gear control systems installed in units, control • an incorrect position in the 3-way valve, or similar, in the
boxes, switchboards or bridge consoles are to be sepa- constant delivery pump system is detected.
rated as far as practicable.
Where physical separation is not practicable, separation 2.4.3 Control system
may be achieved by means of a fire-retardant plate. In the event of a failure of electrical power supply to the
steering gear control systems, an audible an visual alarm
f) All electrical components of the steering gear control shall be given on the navigating bridge.
systems are to be duplicated. This does not require
duplication of the steering wheel or steering lever. 2.4.4 Rudder angle indication
g) If a joint steering mode selector switch (uniaxial switch) The angular position of the rudder is to be:
is employed for both steering gear control systems, the a) indicated on the navigating bridge, if the main steering
connections for the control systems are to be divided gear is power operated. The rudder angle indication is
accordingly and separated from each other by an isolat- to be independent of the steering gear control system
ing plate or air gap. and be supplied through the emergency switchboard, or
h) In the case of double follow-up control, the amplifier is by an alternative and independent source of electrical
to be designed and fed so as to be electrically and power such as that referred to in [2.3.2], item e);
mechanically separated. In the case of non-follow-up b) recognisable in the steering gear compartment.

214 Bureau Veritas April 2007

 Pt C, Ch 1, Sec 11

2.4.5 Summary table Note 1: The mentioned diameter is to be taken as having been cal-
Displays and alarms are to be provided in the locations culated for rudder stock of mild steel with a yield stress of 235
N/mm2, i.e. with a material factor k1 = 1.
indicated in Tab 5.
3.3.2 Auxiliary steering gear
3 Design and construction - Requirements The auxiliary steering gear and rudder stock shall be:
for cargo ships of 500 tons gross ton-
a) of adequate strength and capable of steering the ship at
nage or more and for passenger ships navigable speed and of being brought speedily into
action in an emergency
3.1 Application
b) capable of putting the rudder over from 15° on one side
3.1.1 The provisions of this Article apply in addition to to 15° on the other side in not more than 60s with the
those of Article [2]. ship at its deepest seagoing draught and running ahead
at one half of the maximum ahead service speed or 7
knots, whichever is the greater, and
3.2 General
c) operated by power where necessary to meet the
3.2.1 Unless expressly provided otherwise, every ship shall requirements of b) and in any case when the Society
be provided with main steering gear and auxiliary steering requires a rudder stock of over 230 mm diameter in way
gear to the satisfaction of the Society. of the tiller, excluding strengthening for navigation in ice.
Note 1: The mentioned diameter is to be taken as having been cal-
3.3 Strength, performance and power opera- culated for rudder stock of mild steel with a yield stress of 235
tion of the steering gear N/mm2, i.e. with a material factor k1 = 1.

3.3.1 Main steering gear

The main steering gear and rudder stock shall be:
3.4 Control of the steering gear
a) of adequate strength and capable of steering the ship at 3.4.1 Main and auxiliary steering gear control
maximum ahead service speed which shall be demon-
Steering gear control shall be provided:
strated
b) capable of putting the rudder over from 35° on one side a) for the main steering gear, both on the navigation bridge
to 35° on the other side with the ship at its deepest sea- and in the steering gear compartment
going draught and running ahead at maximum ahead b) where the main steering gear is arranged in accordance
service speed and, under the same conditions, from 35° with [3.5.2], by two independent control systems, both
on either side to 30° on the other side in not more than operable from the navigation bridge and the steering
28s gear compartment. This does not require duplication of
c) operated by power where necessary to meet the the steering wheel or steering lever. Where the control
requirements of b) and in any case when the Society system consists in a hydraulic telemotor, a second inde-
requires a rudder stock of over 120 mm diameter in way pendent system need not be fitted, except in a tanker,
of the tiller, excluding strengthening for navigation in ice, chemical tanker or gas carrier of 10 000 gross tonnage
and and upwards
d) so designed that they will not be damaged at maximum c) for the auxiliary steering gear, in the steering gear com-
astern speed; however, this design requirement need partment and, if power operated, it shall also be opera-
not be proved by trials at maximum astern speed and ble from the navigation bridge and to be independent of
maximum rudder angle. the control system for the main steering gear.

Table 5: Location of displays and alarms

Alarms Location
Item Display (audible Navigation Engine Steering gear
and visible) Bridge Control Room compartment
Power failure of each power unit X X X
Indication that electric motor of each power unit is running X X X
Overload of electric motor of each power unit X X X
Phase failure of electric motor of each power unit X X X
Low level of each hydraulic fluid reservoir X X X
Power failure of each control system X X X
Hydraulic lock X X
Rudder angle indicator X X X

April 2007 Bureau Veritas 215

Pt C, Ch 1, Sec 11

3.4.2 Control systems operable from the navigating 3.5.5 Hydraulic locking
bridge Where the steering gear is so arranged that more than one
Any main and auxiliary steering gear control system opera- system (either power or control) can be simultaneously
ble from the navigating bridge shall comply with the follow- operated, the risk of hydraulic locking caused by single fail-
ing: ure is to be considered.
• if electrical, it shall be served by its own separate circuit
supplied from a steering gear power circuit from a point 4 Design and construction -
within the steering gear compartment, or directly from Requirements for cargo ships of less
switchboard busbars supplying that steering gear power than 500 tons gross tonnage and for
circuit at a point on the switchboard adjacent to the
supply to the steering gear power circuit fishing vessels
• means shall be provided in the steering gear compart-
4.1 Application
ment for disconnecting any control system operable
from the navigation bridge from the steering gear it 4.1.1 The provisions of this Article apply in addition to
serves those of Article [2].
• the system shall be capable of being brought into opera-
tion from a position on the navigating bridge 4.2 General
• in the event of failure of electrical power supply to the
4.2.1 Unless expressly provided otherwise, every ship is to
control system, an audible and visual alarm shall be
be provided with main steering gear and auxiliary steering
given on the navigation bridge, and
gear to the satisfaction of the Society.
• short-circuit protection only shall be provided for steer-
ing gear control supply circuits. 4.3 Strength, performance and power opera-
tion of the steering gear
3.5 Availability
4.3.1 Main steering gear
3.5.1 Arrangement of main and auxiliary steering The main steering gear and rudder stock are to be:
gear
a) of adequate strength and capable of steering the ship at
The main steering gear and the auxiliary steering gear shall maximum ahead service speed, which is to be demon-
be so arranged that the failure of one will not render the strated
other inoperative. b) capable of putting the rudder over from 35° on one side
to 35° on the other side with the ship at its deepest sea-
3.5.2 Omission of the auxiliary steering gear
going draught and running ahead at maximum ahead
Where the main steering gear comprises two or more identi- service speed and, under the same conditions, from 35°
cal power units, auxiliary steering gear need not be fitted, on either side to 30° on the other side in not more than
provided that: 28s
a) in a passenger ship, the main steering gear is capable of c) operated by power where necessary to fulfil the require-
operating the rudder as required in [3.3.1] while any ments of b), and
one of the power units is out of operation d) so designed that they will not be damaged at maximum
b) in a cargo ship, the main steering gear is capable of astern speed; however, this design requirement need not
operating the rudder as required in [3.3.1] while operat- be proved by trials at maximum astern speed and maxi-
ing with all power units mum rudder angle.

c) the main steering gear is so arranged that after a single 4.3.2 Auxiliary steering gear
failure in its piping system or in one of the power units, The auxiliary steering gear is to be:
the defect can be isolated so that steering capability can
a) of adequate strength and sufficient to steer the ship at
be maintained or speedily regained.
navigable speed and capable of being brought speedily
Steering gear other than of the hydraulic type is to achieve into action in an emergency,
standards equivalent to the requirements of this paragraph b) capable of putting the rudder over from 15° on one side
to the satisfaction of the Society. to 15° on the other side in not more than 60s with the
ship at its deepest seagoing draught and running ahead
3.5.3 Hydraulic power supply at one half of the maximum ahead service speed or 7
The hydraulic system intended for main and auxiliary steer- knots, whichever is the greater, and
ing gear is to be independent of all other hydraulic systems c) operated by power where necessary to meet the require-
of the ship. ments of b).
3.5.4 Non-duplicated components 4.3.3 Hand operation
Special consideration is to be given to the suitability of any Hand operation of steering gear is permitted when it
essential component which is not duplicated. requires an effort less than 160 N.

216 Bureau Veritas April 2007

 Pt C, Ch 1, Sec 11

4.4 Control of the steering gear 5.1.3 Equivalent rudder stock diameter
Where the rudders are served by a common actuating sys-
4.4.1 Control of the main steering gear
tem, the diameter of the rudder stock referred to in [3.3.1],
a) Control of the main steering gear is to be provided on item c) and [4.3.1] is to be replaced by the equivalent diam-
the navigation bridge. eter d obtained from the following formula:
b) Where the main steering gear is arranged in accordance
with [4.5.2], two independent control systems are to be
provided, both operable from the navigation bridge.
d = 3 ∑d
j
j
3

This does not require duplication of the steering wheel

or steering lever. with:
dj : Rule diameter of the upper part of the rudder
4.4.2 Control of the auxiliary steering gear stock of each rudder in way of the tiller, exclud-
a) Control of the auxiliary steering gear is to be provided ing strengthening for navigation in ice.
on the navigation bridge, in the steering gear compart-
ment or in another suitable position.
5.2 Synchronisation
b) If the auxiliary steering gear is power operated, its con-
trol system is also to be independent of that of the main 5.2.1 General
steering gear.
A system for synchronising the movement of the rudders is
to be fitted, either:
4.5 Availability
• by a mechanical coupling, or
4.5.1 Arrangement of main and auxiliary means for • by other systems giving automatic synchronising adjust-
actuating the rudder ment.
The main steering gear and the auxiliary means for actuat-
ing the rudder are to be arranged so that a single failure in 5.2.2 Non-mechanical synchronisation
one will not render the other inoperative.
Where the synchronisation of the rudder motion is not
4.5.2 Omission of the auxiliary steering gear achieved by a mechanical coupling, the following provi-
sions are to be met:
Where the main steering gear comprises two or more iden-
tical power units, auxiliary steering gear need not be fitted, a) the angular position of each rudder is to be indicated on
provided that the main steering gear is capable of operating the navigation bridge
the rudder:
b) the rudder angle indicators are to be independent from
a) as required in [4.3.1], item b), while operating with all each other and, in particular, from the synchronising
power units system
b) as required in [4.3.2], item b), while any one of the
c) in case of failure of the synchronising system, means are
power units is out of operation.
to be provided for disconnecting this system so that
4.5.3 Hydraulic power supply steering capability can be maintained or rapidly
regained. See also Pt D, Ch 7, Sec 4, [7.2.1].
Hydraulic power installations supplying steering gear may
also supply other equipment at the same time provided that
the operation of the steering gear is not affected: 6 Design and construction -
a) by the operation of this equipment, or Requirements for ships equipped
b) by any failure of this equipment or of its hydraulic sup- with thrusters as steering means
ply piping.
6.1 Principle
5 Design and construction -
Requirements for ships equipped with 6.1.1 General
several rudders The main and auxiliary steering gear referred to in [3] and
[4] may consist of thrusters of the following types:
5.1 Principle • azimuth thrusters

5.1.1 General • water-jets

In addition to the provisions of Articles [2], [3] and [4], as • cycloidal propellers
applicable, ships equipped with two or more aft rudders are
to comply with the provisions of the present Article. complying with the provisions of Ch 1, Sec 12, as far as
applicable.
5.1.2 Availability
Where the ship is fitted with two or more rudders, each 6.1.2 Actuation system
having its own actuation system, the latter need not be Thrusters used as steering means are to be fitted with a main
duplicated. actuation system and an auxiliary actuation system.

April 2007 Bureau Veritas 217

Pt C, Ch 1, Sec 11

6.1.3 Control system 7.2 Rudder actuator installation

Where the steering means of the ship consists of two or
more thrusters, their control system is to include a device 7.2.1
ensuring an automatic synchronisation of the thruster rota-
tion, unless each thruster is so designed as to withstand any a) Rudder actuators are to be installed on foundations of
additional forces resulting from the thrust exerted by the strong construction so designed as to allow the transmis-
other thrusters. sion to the ship structure of the forces resulting from the
torque applied by the rudder and/or by the actuator,
considering the strength criteria defined in [2.1.3] and
6.2 Use of azimuth thrusters
[7.3.1]. The structure of the ship in way of the founda-
6.2.1 Azimuth thrusters used as sole steering means tions is to be suitably strengthened.
Where the ship is fitted with one azimuth thruster used as b) Where the rudder actuators are bolted to the hull, the
the sole steering means, this thruster is to comply with grade of the bolts used is not to be less than 8.8. Unless
[3.3.1] or [4.3.1], as applicable, except that: the bolts are adjusted and fitted with a controlled tight-
a) the main actuation system is required to be capable of a ening, strong shocks are to be fitted in order to prevent
rotational speed of at least 0,4 RPM and to be operated any lateral displacement of the rudder actuator.
by power where the expected steering torque exceeds
1,5 kN⋅m 7.3 Overload protections
b) the auxiliary actuation system is required to be capable
of a rotational speed of at least 0,1 RPM and to be oper- 7.3.1 Mechanical rudder stops
ated by power where the expected steering torque
exceeds 3 kN⋅m. a) The steering gear is to be provided with strong rudder
stops capable of mechanically stopping the rotation of
6.2.2 Azimuth thrusters used as auxiliary steering the rudder at an angle slightly greater than its maximum
gear working angle. Alternatively, these stops may be fitted
Where the auxiliary steering gear referred to in [3.2.1] or on the ship to act on another point of the mechanical
[4.2.1] consists of one or more azimuth thrusters, at least transmission system between the rudder actuator and
one such thruster is to capable of: the rudder blade. These stops may be built in with the
• steering the ship at maximum ahead service speed actuator design.
• being brought speedily into action in case of emergency b) The scantlings of the rudder stops and of the compo-
• a rotational speed of at least 0,4 RPM. nents transmitting to the ship’s structure the forces
applied on these stops are to be determined for the
The auxiliary actuation system referred to in [6.1.2] need
greater value of the torques TR or TG.
not be fitted.
Where TG ≥1,5TR , the rudder stops are to be fitted
6.2.3 Omission of the auxiliary actuation system between the rudder actuator and the rudder stock,
Where the steering means of the ship consists of two inde- unless the rudder stock as well as all the components
pendent azimuth thrusters or more, the auxiliary actuation transmitting mechanical forces between the rudder
system referred to in [6.1.2] need not be fitted provided that: actuator and the rudder blade are suitably strengthened.
• the thrusters are so designed that the ship can be steered
with any one out of operation 7.3.2 Rudder angle limiters
• the actuation system of each thruster complies with a) Power-operated steering gear is to be provided with pos-
[6.2.1], item b). itive arrangements, such as limit switches, for stopping
the gear before the rudder stops are reached. These
6.3 Use of water-jets arrangements are to be synchronised with the gear itself
and not with the steering gear control.
6.3.1 The use of water-jets as steering means will be given
special consideration by the Society. b) For power-operated steering gears and where the rudder
may be oriented to more than 35° at very reduced
7 Arrangement and installation speed, it is recommended to fit a limit system 35° for full
speed. A notice is to be displayed at all steering wheel
stations indicating that rudder angles of more than 35°
7.1 Steering gear room arrangement are to be used only at very reduced speed.
7.1.1 The steering gear compartment shall be:
7.3.3 Relief valves
a) readily accessible and, as far as practicable, separated
from machinery spaces, and Relief valves are to be fitted in accordance with [2.2.5].
b) provided with suitable arrangements to ensure working
access to steering gear machinery and controls. These 7.3.4 Buffers
arrangements shall include handrails and gratings or Buffers are to be provided on all ships fitted with mechani-
other non-slip surfaces to ensure suitable working condi- cal steering gear. They may be omitted on hydraulic gear
tions in the event of hydraulic fluid leakage. equipped with relief valves or with calibrated bypasses.

218 Bureau Veritas April 2007

 Pt C, Ch 1, Sec 11

7.4 Means of communication • cylindrical shells of hydraulic cylinders, rams and

piston rods
7.4.1 A means of communication is to be provided • tillers, quadrants
between the navigation bridge and the steering gear com-
partment. • rotors and rotor housings for rotary vane steering gear
• hydraulic pump casings
If electrical, it is to be fed through the emergency switch-
board or to be sound powered. • and hydraulic accumulators, if any,
are to be duly tested, including examination for internal
7.5 Operating instructions defects, in accordance with the requirements of NR216
Materials and Welding.
7.5.1 For steering gear comprising two identical power b) A works’ certificate may be accepted for low stressed
units intended for simultaneous operation, both normally parts, provided that all characteristics for which verifica-
provided with their own (partly or mutually) separate con- tion is required are guaranteed by such certificate.
trol systems, the following standard notice is either to be
placed on a signboard fitted at a suitable place on the steer- 8.2.2 Hydraulic piping, valves and accessories
ing control post on the bridge or incorporated into the oper-
ation manual: Tests for materials of hydraulic piping, valves and accessories
are to comply with the provisions of Ch 1, Sec 10, [20.3].
CAUTION

IN SOME CIRCUMSTANCES WHEN 2 POWER UNITS ARE 8.3 Inspection and tests during manufactur-
RUNNING SIMULTANEOUSLY, THE RUDDER MAY NOT ing
RESPOND TO THE HELM. IF THIS HAPPENS STOP EACH
PUMP IN TURN UNTIL CONTROL IS REGAINED. 8.3.1 Components subject to pressure or
transmitting mechanical forces

8 Certification, inspection and testing a) The mechanical components referred to in [8.2.1] are to
be subjected to appropriate non-destructive tests. For
hydraulic cylinder shells, pump casings and accumula-
8.1 Type tests of hydraulic pumps tors, refer to Ch 1, Sec 3.

b) Defects may be repaired by welding only on forged

8.1.1 Each type of power unit pump is to be subjected in the parts or steel castings of weldable quality. Such repairs
workshop to a type test of not less than 100 hours’ duration. are to be conducted under the supervision of the Sur-
The test arrangements are to be such that the pump may run veyor in accordance with the applicable requirements
both: of NR216 Materials and Welding.

• in idling conditions, and 8.3.2 Hydraulic piping, valves and accessories

• at maximum delivery capacity at maximum working Hydraulic piping, valves and accessories are to be
pressure. inspected and tested during manufacturing in accordance
with Ch 1, Sec 10, [20], for a class I piping system.
During the test, idling periods are to be alternated with peri-
ods at maximum delivery capacity at maximum working 8.4 Inspection and tests after completion
pressure. The passage from one condition to another is to
occur at least as quickly as on board.
8.4.1 Hydrostatic tests
During the test, no abnormal heating, excessive vibration or a) Hydraulic cylinder shells and accumulators are to be
other irregularities are permitted. subjected to hydrostatic tests according to the relevant
provisions of Ch 1, Sec 3.
After the test, the pump is to be disassembled and inspected.
b) Hydraulic piping, valves and accessories and hydraulic
Note 1: Type tests may be waived for a power unit which has been
pumps are to be subjected to hydrostatic tests according
proven to be reliable in marine service.
to the relevant provisions of Ch 1, Sec 10, [20.4].

8.2 Testing of materials 8.4.2 Shipboard tests

After installation on board the ship, the steering gear is to be
8.2.1 Components subject to pressure or subjected to the tests detailed in Ch 1, Sec 15, [3.11].
transmitting mechanical forces
8.4.3 Sea trials
a) Materials of components subject to pressure or transmit-
ting mechanical forces, specifically: For the requirements of sea trials, refer to Ch 1, Sec 15.

April 2007 Bureau Veritas 219