In order to turn a rudder a force is applied to a tiller. As ships became larger the rudders also increased in size and the manpower necessary to turn the rudder increased. Brunel's large steamship Great Eastern was the first ship fitted with a powered steering gear; this was a steam engine-driven system developed by John McFarlane Gray and it was fitted in 1867. Steering gear powered by steam engines continued to be used in ships until the 1930s by which time the ram-type hydraulic steering gear proved more efficient and more reliable. This consisted of hydraulically driven rams connected with the tiller attached to the rudder stock. The hydraulic rams are supplied with oil from pumps which are driven by electric motors. Control instructions are relayed to the steering gear control system from the bridge by electronic means or by means of a hydraulic telemotor system.
The most modern system is the rotary vane steering gear which is very compact compared with the more traditional hydraulic ram type. A cylindrical actuator unit sits on top of the rudder stock with the vaned rotor connected to the rudder stock. The actuator cylinder has fixed vanes or stoppers which divide the actuator into a number of sections, usually two or three, and each section houses one of the rotor's vanes. The steering gear pump forces oil to one side of each rotor vane and takes oil from the other side of the rotor vane, thus causing the rotor to turn. As the rotor is connected to the rudder this causes the rudder to turn to the desired angle. As with the ram-type hydraulic steering gear, the rotary vane steering gear for large ships, particularly oil tankers, has two separate hydraulic pump systems so that if one fails the other is available to steer the ship.
All steering gear in large ships can be controlled automatically by gyroscopic pilots. The ship's course is set on a gyro compass, and if it strays from this setting the rudder is automatically moved to bring the ship back on course. See also vane self-steering gear.
Subjects: Maritime History.