Rudder angle indicator | Definition, Working and Circuit Diagram

Rudder angle indicator | Definition, Working and Circuit Diagram
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.

Basic Steering gear system

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.
Non Follow-up Steering System
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.

Auto & Follow up Steering System
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.

Electronic Steering Control
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.

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Author Arpit Singh & Amit                                                                Article Requested by: kesavan s

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