Steering Gears Maintenance
Steering Gears Maintenance
Steering Gears Maintenance
a
M
e
c
an
n
nte
Rudder
movement
too slow.
a. repair/replace as
reqd.
b. valve to set proper
c. Blow out air and
rectify leakage chances
and maintain oil level in
tank
h. check up controls
c.Adjust rudder to be in
mid ship w.r to helm
temporarily.
REPAIR /REPLACE
STOCK URGRNTLY
Control stiff to
operate but free
binding in hunting gear, pump
when disconnected stroke mechanism or control
from gear.
valves
a. air in system
Noise and vibration b. motor-pump misalignment
from pump
c. mechanical pump fault
a.air in system
b.motor-pump misalignment
c.mechanical pump fault
When checking steering in still waters, rudder locking valves can be used to simulate a load to
the system.
Trials
The steering gear is to be tried out on the trial trip in order to demonstrate to the
Surveyor's satisfaction that the requirements of the Rules have been met.
The trial is to include the operation of the following:
(a) The steering gear, including demonstration of the performances required For the
main steering gear trial, the propeller pitch of controllable pitch propellers is to be at
the maximum design pitch approved for the maximum continuous ahead RPM. If
the vessel cannot be tested at the deepest draught, alternative trial conditions may
be specially considered. In this case, for the main steering gear trial, the speed of
the ship corresponding to the maximum continuous revolutions of the main engine
should apply;
(b) The steering gear power units, including transfer between power units;
(c) The isolation of one power actuating system, checking the time for regaining
steering capability;
(d) The hydraulic fluid recharging system;
(e) The emergency power supply required
(f) The steering gear controls, including transfer of control and local control;
(g) The means of communication between the steering gear compartment and the
wheelhouse, also the engine room, if applicable;
(h) The alarms and indicators.
(j) Where the steering gear is designed to avoid hydraulic locking this feature shall
be demonstrated.
Test items (d), (g), (h) and (j) may be effected at the dockside.
Additional requirements
For tankers, chemical tankers or gas carriers of 10 000 tons gross and above
(a) The main steering gear is to be so arranged that in the event of loss of steering
capability due to a single failure in any part of one of the power actuating
systems of the main steering gear, excluding the tiller, quadrant or components
serving the same purpose, or seizure of the rudder actuators, steering capability
is to be regained in not more than 45 seconds after the loss of one power
actuating system.
b) The main steering gear is to comprise either:
(i) two independent and separate power actuating systems, each capable of
meeting the requirements
or
(ii) at least two identical power actuating systems which, acting simultaneously in
normal operation, are capable of meeting the requirements of 2.1.2(b). Where
necessary to comply with these requirements, inter-connection of hydraulic
power actuating systems is to be provided. Loss of hydraulic fluid from one
system is to be capable of being detected and the defective system
automatically isolated so that the other actuating system or systems remain fully
operational.
(c) Steering gears other than of the hydraulic type are to achieve equivalent
Additional requirements
For tankers, chemical tankers or gas carriers of 10 000 tons gross and
upwards but of less than 100 000 tons deadweight
Solutions other than those set out which need not apply the single failure criterion
to the rudder actuator or actuators, may be permitted provided that an equivalent
safety standard is achieved and that:
(a) Following loss of steering capability due to a single failure of any part of the
piping system or in one of the power units, steering capability is regained within 45
seconds; and
(b) Where the steering gear includes only a single rudder actuator special
consideration is given to stress analysis for the design including fatigue analysis
and fracture mechanics analysis, as appropriate, the material used, the installation
of sealing arrangements and the testing and inspection and provision of effective
maintenance..
Manufacturers of steering gear who intend their product to comply with the
requirements of the `Guidelines' are to submit full details when plans are
forwarded for approval
Additional requirements
Acceptance of non-duplicated rudder actuators for tankers, chemical
tankers and gas carriers of 10 000 tons gross and upwards but of less
than 100 000 tons deadweight
Parts subject to internal hydraulic pressure or transmitting mechanical forces to
the rudder-stock are to be made of duly tested ductile materials complying with
recognized standards. Materials for pressure retaining components are to be in
accordance with recognized pressure vessel standards. These materials are not
to have an elongation less than 12 per cent and a tensile strength in excess of
650 N/mm2.
Design pressure. The design pressure should be assumed to be at least equal
to the greater of the following:
(a) 1,25 times the maximum working pressure to be expected under the
operating conditions required
(b) The relief valve(s) setting.
contd.
Additional requirements
Analysis. In order to analyse the design the following are required:
(a) The manufacturers of rudder actuators should submit detailed calculations
showing the suitability of the design for the intended service.
(b) A detailed stress analysis of pressure retaining parts of the actuator should be
carried out to determine the stresses at the design pressure.
(c) Where considered necessary because of the design complexity or
manufacturing procedures, a fatigue analysis and fracture mechanics analysis
may be required. In connection with these analyses, all foreseen dynamic loads
should be taken into account. Experimental stress analysis may be required in
addition to, or in lieu of, theoretical calculations depending upon the complexity of
the design.
The assumption for dynamic loading for fatigue and fracture mechanics analysis
where required are to be submitted for appraisal. Both the case of high cycle and
cumulative fatigue are to be considered.
For the purpose of determining the general scantlings of parts of rudder actuators
subject to internal hydraulic pressure the allowable stresses should not exceed
limits calculated using the materials to be used
Pressure retaining parts not requiring fatigue analysis and fracture mechanics
analysis may be accepted on the basis of a certified burst test and the detailed
stress analysis required The minimum bursting pressure should be calculated
using set formulae:
Construction details
The construction should be such as to minimize local concentrations of stress.
(a) The welding details and welding procedures should be approved.
(b) All welded joints within the pressure boundary of a rudder actuator or
connection parts transmitting mechanical loads should be full penetration type
or of equivalent strength.
Oil seals forming part of the external pressure boundary are to be of the metal
upon metal type or of an equivalent type
Isolating valves are to be fitted at the connection of pipes to the actuator, and
should be directly mounted on the actuator.
Relief valves for protecting the rudder actuator against over-pressure as
required to comply with the following:
(a) The setting pressure is not to be less than 1,25 times the maximum working
pressure expected under operating conditions
(b) The minimum discharge capacity of the relief valve(s) is to be not less than
110 per cent of the total capacity of all pumps which provided power for the
actuator. Under such conditions the rise in pressure should not exceed 10 per
cent of the setting pressure. In this regard due consideration should be given to
extreme foreseen ambient conditions in respect of oil viscosity.
POWER
The peak power that a steering gear must develop is the product of the
maximum torque (T) usually at hard over with the ship traveling at full
speed, and the maximum speed (S) of rudder movement i.e. Power
(max) - T x S.
The combination of maximum power and speed only exists for 2 or 3
seconds during each manoeuvre; so clearly the average power required
to operate the steering gear is considerably below the peak. Because
the steering gear must have sufficient power to overcome friction and
still have ample reserve of power, the value for used in the foregoing
expression is significantly higher than that used in the expression for
rudder torque. When considering the diameter of the rudder stock,
bending and shear stresses must be taken into account.
Special requirements
Owners may specify additional requirements such as faster hard-over to hard-over
time, strength of components above that required by the Rules, additional control
points and additional duplication,
New tankers of 100 000dwt and above-shall comply with the following
The main steering gear shall comprise of either
two independent and separate power actuating systems each capable of
meeting the hard over port to 30o starboard in 28 sec requirements,
or
at least two identical power actuating systems which acting
simultaneously in normal operation, shall be capable of meeting the
hard over requirements. Where necessary to comply with this
requirement inter connection of hydraulic power systems shall be
provided. Loss of hydraulic fluid from one system shall be capable of
being detected and the defective system isolated so that the other
system shall remain fully operational
In the event of loss of steering capability due to a single failure other than the
tiller, quadrant or components serving the same purpose (these are excluded
from single failure concepts), or seizure of the rudder actuators. The steering
capability shall be regained in not less than 45 seconds after the loss of one
power actuating system.
Steering gear other than hydraulic should meet the same standards
Relief Valves
Hydraulic actuators are provided with relief and bypass
valves between complementary pairs of cylinders or
chambers of vane gears. The relief valves are set to lift at
pressures above the normal maximum.
Bypass Valves
The bypass valves are normally closed but can be opened on a
two cylinder gear to enable emergency steering to be used. On
a four cylinder gear one pair of cylinders can be bypassed
while the other pair provide emergency steering at a reduced
torque, an instruction plate is fitted over the controls valve
block giving a combination of failures and which valves have to
be open or shut to cope with the emergency etc. It should be
noted that if one ram or cylinder in a four ram system breaks
down, then never isolate the cylinder diagonally opposite the
damaged unit, since the steering gear will not operate due to
the fact that the remaining two cylinders will be either on all
pressure or on all suction at the same time.
Isolating Valves
Another
Another method
method of
of protection
protection against
against rotation
rotation of
of the
the stand by
by
pump
pump is
is to
to fit
fit Servo
Servo pressure operated automatic change over
valves
valves in
in the
the pipelines;
pipelines; these
these ensure
ensure that
that the
the pump
pump can
can only be
be
started
started in the unloaded condition (neutral) and in addition
prevents
prevents the stand by pump from being motored by the pump
in
in service.
service.
On
On some
some ships
ships it
it has
has been
been discovered
discovered that
that the
the ball
ball bearing
bearing
races
races on
on the
the stand-by
stand-by pump
pump have
have been
been failing
failing due
due to
to brinelling
brinelling
of
of the
the ball
ball bearings,
bearings, caused
caused by
by ship
ship vibrations,
vibrations, and
and in
in these
these
cases
cases it
it is usual
usual to
to fit
fit devices
devices which
which allows
allows the
the stand
stand by
by pump
pump
to
to be
be motored
motored slowly.
slowly.
When
When fixed
fixed delivery
delivery pumps
pumps are
are duplicated
duplicated in
in supplying
supplying oil
oil to
to a
a
common
common hydraulically
hydraulically operated
operated control
control valve,
valve, an
an automatic
automatic
change
change over
over valve
valve can
can be
be fitted
fitted which
which will
will isolate
isolate the stand by
pump
pump when
when it
it is
is at
at rest,
rest, but
but will
will connect
connect it to the actuator when
the
the pump
pump is started up.
Circumstances when
more than one steering power unit required.
In areas where navigation demands special caution,
ships shall have more than one steering gear power
unit in operation when such units are capable of
simultaneous operation.