A hydraulic steering gear consists of a bridge control which applies helm, an engine control which is operated jointly by the helm and hunting gear (when fitted) and a power pump and rudder actuator which constitutes the steering engine.

Telemotor systems

The telemotor system consists of a transmitter on the bridge and a receiver fitted on the steering gear forming a part of the hunting gear. The system may be electrical or hydraulic or a combination of the two.

Most modern vessels are fitted with electric or electro-hydraulic systems. Due to the increasing size of vessels pipe runs have lengthen causing lags in the operation of the receiver in hydraulic systems. In addition hydraulic only systems generally require more maintenance.

Hydraulic transmitter

Shown above is a typical hydraulic transmitter unit. The pinion driving the pistons is turned by the bridge wheel.

The casing is usually gun metal, with bronze rams, and copper pipes are led in by frilled leads on the casting.

To test the system, with the steering gear actuating pumps stopped, the wheel may be lashed at hard over and the pressure recorded. It should maintain this pressure for some time

To allow for expansion in the system and to allow topping up a 'by-pass valve' is fitted. It will also act as a safety valve.

Author note:
The main problem appears to be the effect of air entrained within it. Thus regular venting of the system is required.

By-pass valve

The operating rod is pushed down making both line common whenever the wheel is at midships, generally by a cam fitted to the pinion. This ensures they system is always balanced

The charging valves are opened only when filling or flushing.

The moving cylinder is attached to the hunting gear. When the bridge wheel is turned hydraulic pressure acts on the cylinder causing it to move. This in turn moves the hunting gear. The steering gear is then moved to compensate until the hunting gear is moved back to the neutral position. The total movement of the receiver is limited by stops.

Electro-hydraulic type telemotor system

Shown is a very simple system capable of operating a steering hunting gear. A pressure relief valve would normally be fitted after the valve and across the pump to prevent over pressurisation of the system.

The signal is derived from the action on the steering wheel, created by the autopilot or directly from the non-follow up control levers.

Telemotor fluid

should be a good quality mineral oil with the following properties;

1. low pour point
2. non sludge forming
3. non corrosive
4. good lubricating properties
5. high flash point
6. low viscosity