A telemotor is the remote-control link that carries the helm order from the bridge to the steering gear room. It consists of a transmitter on the bridge, a receiver at the steering gear, and the pipes or cables joining them.
This guide is written for deck and engineering cadets and junior officers. It explains what the telemotor does, its parts, how hydraulic and electric telemotors work, and how the system is maintained.
What Is the Function of a Telemotor?
The telemotor transmits the rudder angle ordered at the wheel to the steering gear control unit, often 100 metres or more aft. It turns a small movement on the bridge into a matching movement at the steering gear.
The telemotor does not move the rudder itself. It only delivers the order. The steering gear power unit supplies the force that turns the rudder and holds it at the ordered angle.
- Transmits the order: the wheel or tiller position becomes a fluid displacement or an electrical signal.
- Reproduces it aft: the receiver moves the control linkage of the steering gear by a proportional amount.
- Returns to midships: on a hydraulic telemotor, centring springs return the receiver, and with it the wheel, to midships when the wheel is released.
Where Does the Telemotor Fit in the Steering Gear System?
The telemotor is the first of the three main parts of the steering gear: the telemotor, the control unit and the power unit. It sends the order, the control unit converts it, and the power unit moves the rudder.
The propeller drives the ship, but the rudder changes its heading. The steering gear turns the rudder on its stock, and the telemotor tells the steering gear how far to turn it.
The control unit, power unit, types of steering gear and SOLAS performance requirements are covered in the main guide to steering gear on ships.
What Are the Parts of a Hydraulic Telemotor?
A hydraulic telemotor has a bridge transmitter, a receiver in the steering gear room and two pipes between them. A charging unit fills the system, and a bypass valve and replenishing tank sit on the transmitter.
Transmitter
The transmitter is built into the steering pedestal on the ship’s bridge, under the wheel. It is a cylinder on a pedestal base containing a piston, or a pair of rams, driven by a rack and pinion from the wheel.
Turning the wheel to starboard pushes fluid into one pipe and draws it from the other. Turning to port reverses the flow.
Receiver
The receiver sits in the steering gear compartment, mounted on or next to the steering gear. Its rams are fixed, and the cylinder body slides over them when fluid is displaced.
As the cylinder moves it compresses centring springs and moves the control linkage, called the hunting gear or floating lever. When the wheel is released, the springs return the receiver to midships.
Bypass Valve and Replenishing Tank
The bypass valve connects the two sides of the system when the wheel is at midships. This equalises pressure and lets fluid expand or contract with temperature without moving the rudder.
The replenishing tank on the transmitter keeps the system full and makes up for small leaks.
Charging Unit
The charging unit is a small tank and hand pump used to fill the system and purge air after maintenance. Air in the pipes is the most common cause of sluggish telemotor response.
How Does a Hydraulic Telemotor Work?
Turning the wheel moves a piston in the transmitter, which pushes fluid through the pipes to the receiver. The receiver cylinder moves by a matching amount and shifts the steering gear control linkage, which starts the rudder moving.
- The helmsman turns the wheel. The pinion drives the rack and moves the transmitter piston.
- Fluid is displaced into one pipe and drawn back from the other, so the system stays closed.
- The receiver cylinder slides over its fixed rams, compressing the centring springs.
- Linkage from the receiver moves the floating lever, which puts the variable delivery pump on stroke.
- The pump sends oil to the rudder actuator, and the rudder starts to turn.
- Feedback from the rudder stock moves the other end of the floating lever. When the rudder reaches the ordered angle, the pump returns to neutral.
On a four-ram steering gear the principle is the same. The telemotor receiver moves the floating lever, and the pump supplies two pairs of rams instead of one.
How Does an Electric Telemotor Work?
An electric telemotor sends the ordered rudder angle as an electrical signal instead of fluid. The control box compares the order with the actual rudder angle and drives the pump until the difference is zero.
The order from the steering stand is compared with the feedback angle from the rudder. The difference, or deviation signal, becomes a pump control signal in the control box.
This signal drives a torque motor that moves the hydraulic regulator of the pump. Oil from the pump goes to the hydraulic cylinder, and the ram and ram pin rotate the tiller.
On some gears a control spindle, pinned to the cylinder unit, moves the pump control. That is the swash plate of an axial-piston pump or the floating ring of a radial-piston pump.
For manual control, the changeover pin is removed from the cylinder unit and fitted to the local handwheel drive. The gear can then be steered from the steering gear room.
What Are the Types of Telemotor?
There are three types of telemotor: hydraulic, electric and electro-hydraulic. Most modern merchant ships use electric or electro-hydraulic telemotors, while hydraulic telemotors remain on older ships and some smaller craft.
- Hydraulic telemotor: fluid in two pipes links the transmitter and receiver directly. Simple and independent of electrical power, but long pipe runs need regular venting.
- Electric telemotor: the wheel drives a transmitter, such as a synchro or potentiometer. The receiver is an electric motor or actuator at the steering gear.
- Electro-hydraulic telemotor: an electrical signal from the bridge drives a small hydraulic servo at the receiver. This servo moves the steering gear control linkage.
Electric systems allow several control stations, follow-up and non-follow-up modes, and an autopilot to share the same receiver end.
What Safety Features Does a Telemotor System Have?
Telemotor and steering gear control systems have limit switches, a relief valve, and pressure and level alarms. These stop the rudder before it reaches its mechanical stops and warn the crew of oil loss.
- Limit switches stop the gear before the rudder reaches its mechanical stops, set just beyond the 35° hard-over angle.
- Relief valve protects the telemotor if the wheel is forced past the hard-over position.
- Pressure and level sensors raise an audible and visual alarm if hydraulic oil is lost.
- Changeover arrangements let the crew isolate the telemotor and steer locally from the steering gear room.
The alarms required on the bridge come from SOLAS Chapter II-1, Regulations 29 and 30. They cover the steering gear as a whole, rather than the telemotor alone.
How Is a Telemotor Maintained?
Telemotor maintenance means keeping the system full of clean fluid, free of air and free of leaks. The replenishing tank, lubrication points and pipe joints are checked regularly, and the system is vented if response becomes sluggish.
- Fluid level: keep the tank topped up with low-viscosity, non-freezing mineral oil, which also stops internal corrosion.
- Leaks: repair any leak or damage at once, since the steering gear is safety-critical equipment.
- Air venting: vent the system when the wheel feels slow or sluggish to answer.
- Fluid renewal: if venting does not cure sluggish response, drain the system and refill with new oil.
- Lubrication: grease the rack, pinion and linkage points per the maker’s schedule.
- Wheel handling: never force the wheel beyond hard over. Excess pressure strains the gears and seals.
Work on the telemotor is done when the ship is in port or at anchor and the steering gear is not needed. The system is then tested as part of the pre-departure steering gear checks required by SOLAS Chapter V, Regulation 26.
Why Is the Titanic’s Telemotor Famous?
The Titanic’s bronze telemotor still stands on the wreck’s bridge, in its original position. It is the only bridge fitting still where it was in 1912.
It connected the wheels on the bridge to the steering gear under the poop deck. It marks where the quartermaster stood when the ship tried to steer clear of the iceberg.
Related Topics
Frequently Asked Questions
What is a telemotor in a ship?
A telemotor is the remote-control link between the ship’s wheel on the bridge and the steering gear aft. It has a transmitter on the bridge, a receiver at the steering gear, and pipes or cables between them.
What is the function of the telemotor in steering gear?
It transmits the rudder angle ordered at the wheel to the steering gear control unit. The telemotor only carries the order; the power unit supplies the force that moves the rudder.
What are the two main parts of a telemotor?
The transmitter and the receiver. The transmitter is in the steering pedestal on the bridge, and the receiver is mounted on the steering gear in the steering gear room.
Where is the telemotor located on a ship?
The transmitter is on the bridge, under the steering wheel. The receiver is in the steering gear compartment at the stern, directly above the rudder.
What fluid is used in a hydraulic telemotor?
A low-viscosity, non-freezing mineral oil. It must stay fluid in cold weather and protects the cylinders and pipes from internal corrosion.
Why does a telemotor respond sluggishly?
Air in the system is the usual cause, so the first step is to vent it. If venting does not cure the problem, the oil is drained and replaced.
What does the bypass valve in a telemotor do?
It connects both sides of the system when the wheel is at midships. This equalises pressure and allows for fluid expansion with temperature changes.
What is the difference between a telemotor and steering gear?
The telemotor is one part of the steering gear system. It carries the order from the bridge, while the control unit and power unit turn that order into rudder movement.
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