Page 231 - Introduction to Marine Engineering

Chapter 12
Steering gear

The steering gear provides a movement of the rudder in response to a
signal from the bridge. The total system may be considered made up of
three parts, control equipment, a power unit and a transmission to the rudder
stock. The control equipment conveys a signal of desired rudder angle
from the bridge and activates the power unit and transmission system
until the desired angle is reached. The power unit provides the force,
when required and with immediate effect, to move the rudder to the
desired angle. The transmission system, the steering gear, is the means
by which the movement of the rudder is accomplished.
Certain requirements must currently be met by a ship's steering
system. There must be two independent means of steering, although
where two identical power units are provided an auxiliary unit is not
required. The power and torque capability must be such that the rudder
can be swung from 35° one side to 35* the other side with the ship at
maximum speed, and also the time to swing from 35° one side to 30° the
other side must not exceed 28 seconds. The system must be protected
from shock loading and have pipework which is exclusive to it as well as
be constructed from approved materials. Control of the steering gear
must be provided in the steering gear compartment.
Tankers of 10000 ton gross tonnage and upwards must have two
independent steering gear control systems which are operated from the
bridge. Where one fails, changeover to the other must be immediate and
achieved from the bridge position. The steering gear itself must
comprise two independent systems where a failure of one results in an
automatic changeover to the other within 45 seconds. Any of these
failures should result in audible and visual alarms on the bridge.
Steering gears can be arranged with hydraulic control equipment
known as a 'telemeter', or with electrical control equipment. The power
unit may in turn be hydraulic or electrically operated. Each of these
units will be considered in turn, with the hydraulic unit pump being
considered first. A pump is required in the hydraulic system which can
immediately pump fluid in order to provide a hydraulic force that will
move the rudder. Instant response does not allow time for the pump to

211