Steering gear (rotary vane)

A rotary-vane steering gear is a hydraulic actuator that turns the rudder stock directly with vanes inside an annular housing instead of with rams and a tiller. A rotor keyed to the rudder stock carries vanes that sweep against fixed stator vanes; pumping oil into the chambers on one side rotates the rotor and the rudder. It is compact and gives high torque in a small footprint, common where deck space is tight. SOLAS Ch II-1 Reg 29 governs steering gear, requiring a main and an auxiliary system, duplicated power units on many ships, and the ability to put the rudder from 35 degrees one side to 30 degrees the other within 28 seconds.