A device to display the current position of the rudder installed in
the control house of the bridge. In the angle indicator system Rudder is
independent of the steering system and is only for the display. There
is an IMO requirement which states regardless of the steering control
system there must be installed steering indicator system installed on
board. The specification of the rudder angle is required for each
cockpit and steering position in the rudder emergency room.
The
various regulatory authorities vary the requirements of the Rudder
Level Indicator (RAI). DNV needs a second angle indicator independent
bar on deck. Regulation of the Panama canal requires large instruments
(min 192x192mm) Bridge, visible wing operator and IMO pull to train /
MED (ISO 20673) requires that the accuracy of the system is over a
degree.
Rudder angle indicator consists of a control
unit, a transmitter and receiver. This includes indicators with
different dimensions, different scales and rudder angle display.
A
rudder angle indicator consists of a transmitter and a receiver
direction of the rudder rudder. The emitter is connected to the steering
head by means of a lever, etc. in the wheel housing. Communicates
rudder direction and rotation angle for self-synchronization of the
machine in the sender and causes the self-synchronization of the
machine, in the receiver that I have in the wheelhouse or another that
is for with their directions of synchronicity. Self-synchronous
transmitters and display units used in the control angle display systems
are manufactured by various companies refer to names such as Selsyns,
Synchro, and Automatic Syns Telmotors.
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| Non Follow-up Steering System |
Control equipment – conveys a
signal of the desired rudder angle from the bridge to the steering flat
where it is received to activate the power unit and transmission system
until the desired rudder angle is reached. This equipment can be of 2
types (1)hydraulic telemotor systems (tele- means far away in Greek
& motor means motion or movement) & (2) electrical electronic
control equipment.
Hydraulic telemotor systems: The
telemotor employs master and slave principle. The transmitter is
situated on bridge and the receiver at the steering gear unit.
Mechanical movement is transduced hydraulically or electrically for
distance telemetering and is then transduced back again.
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| Auto & Follow up Steering System |
Hydraulic
Transmitter: As the bridge steering wheel is moved to starboard the
rotating pinion causes the RH ram to move down, pushing oil out to the
receiver unit along the RH pipe. The LH ram moves up, so allowing a
space for oil to come from the receiver unit. The fluid being virtually
incompressible, any down movement of the RH produces an identical
movement at the receiver unit. This in turn displaces the same quantity
of fluid which is taken up in the extra space created by the LH ram
moving up. The fluid in the replenishing tank acts as reservoir. The
casing is usually gunmetal with bronze rams, and copper pipes are led in
by drilled leads in the casting. A device (called bypass valve) is
required in the system to allow for variation in oil volume due to
temperature changes and also to allow for equilibrium between both sides
of the system. This bypass valve also has function of topping up the
system in the case of leakages and acts as relief valve in case of
pressure rise.
Bypass valve: Operation can only be
carried out when the wheel is in the mid position. This is achieved by
having the operating rod butting against a circular disc, in mid
position of the wheel the slot in the driven revolving disc allows the
operating rod to be depressed through it. With some types the operating
rod is depressed by hand, whilst with some types the rod is
automatically depressed by a cam each time the wheel passes mid
position. In case of hand operated types the rod is operated at regular
intervals and must be operated when either pressure gauge registers
above 4.5 bar with wheel in mid position. When the rod is depressed both
sides of system are connected thus giving pressure balance. The
connection to the replenishing tank is also joined to both sides of the
system, so that any expansion or contraction of the oil can be
compensated.
Hydraulic Receiver: Consider
the starboard (clockwise) movement of the bridge wheel. The depressed RH
ram pressurizes the right hand side of the system. The pressure force
acts on the central web of the moving cylinder until the movement caused
corresponds to the movement of the ram in the steering telemotor. Oil
is pushed back on the left hand side of the moving cylinder central web
to the steering unit. After a small initial movement the LH sleeve butts
against the nut and further movement by the moving cylinder to the left
compresses the springs. When the steering wheel is returned to mid-ship
the springs, which are under initial compression, return the moving
cylinder to mid position. For port wheel rotation the LH ram of the
steering unit moves down and the receiver moving cylinder goes in the
opposite direction i.e. in this case left to right.
The moving
cylinder is connected by a linkage to the control unit of the steering
engine. Thus any movement of the bridge telemotor unit by wheel rotation
is almost directly operating the control device which causes rotation
of the steering engine and rudder movement.
electrical
electronic control equipment: This system is based on the electrical
and electronic circuits, the monitoring and control of the valves, which
control the movement of the rudder. The system also includes a logic
circuit that prevents the side rudder from reaching its physical limits.
In the steering system can only work, under preset electronic limits.
When the bar has reached a limit, the power of the solenoid valve closes
automatically.
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| Electronic Steering Control |
The system consists of the following
parts: The control unit transmits to the angle of the desired direction
from the bridge in the direction of the plane,Hand Steering without
follow-up, Hand Steering with follow-up and Auto Steering using Gyro
Compass.
The power supply provides the energy to move
the rudder at the desired angle and the transfer unit to move the
motions of the rudder.
The central steering of the
movement of the rudder affect the ship's engines control. And rudder
actuators single unit servo steering is the torque means is applied to
the i-th rudder shaft. Lance or Quadrant
Control system
of the device by means of which the commands from the computer to the
power units of the steering mechanism and other necessary parts are
transmitted to operate the steering. Including transmitters, receivers,
hydraulic control pumps and motors associated hoses and cables.
The
rudder actuator, the element that directly moves to a hydraulic
pressure on the mechanical effect moves the rudder. Wheel drive means
that the parts that transfer the force from the actuator to the aileron
of the flow including the rudder. Power unit means:
- in the case of electrical steering gear ; an electric motor and its associated electrical equipment
- in case of electro-hydraulic steering gear ; an electric motor and its associated equipment and connected pump
- in case of other hydraulic steering gear ; a driving engine and connected pump
Steering Gear Regulations
1.Every ship is to
be provided with two power unit (main and auxiliary) steering gear, each
independent of the other. This is because if one fail another can take
over the power. If however two identical power unit is available, the
presence of stand-by(Auxiliary) is not required.
2.The
capacity of the unit must be such that, it may swing the rudder from
35º on one side to 35º to the other side of the ship with the maximum
speed and at deepest draft.The time required to do so must not exceed 28
Seconds.
3.Steering gear must be power operated if
rudder stock diameter is greater than 120mm. Mostly we use hydraulic
power for operating the rudder post.
Power of the
auxiliary steering shall be such that rudder can be swung from 15º on
one side to 15º to the other in 60 seconds at deepest draft and of 7
knots.
5.Steering gear should be prevented from any
abnormalities, such as overloading, short circuit, overload, and visual
and audible indicator should be available on bridge, ECR and steering
gear room, alarms and trips is also present to minimize the damage.
6.For Hydraulic Oil tank, Low level alarm is present.
7.A
Tanker of 10000 GRT and more must be provided with two steering gear
systems, So in case of failure the steering gear change automatically to
the stand-by Steering gear system within 45 seconds, along-with alarm
for indication. It is provided for a reason, that if in case failure
occur the ship keep moving in the same direction.
#Cover image credit: http://marine-data.co.uk
Author Arpit Singh & Amit Article Requested by: kesavan s
#Cover image credit: http://marine-data.co.uk
Author Arpit Singh & Amit Article Requested by: kesavan s
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