Page 252 - Introduction to Marine Engineering

228 Steering gear

Twin system steering gears

To meet the automatic changeover within the 45 seconds required for
tankers of 10000 ton gross tonnage and above, a number of designs are
available. Two will be described, one for a ram type steering gear and
one for a rotary vane type steering gear. In each case two independent
systems provide the power source to move the tiller, the failure of one
resulting in a changeover to the other. The changeover is automatic and
is achieved within 45 seconds.
The ram type steering gear arrangement is shown diagrammatically in
Figure 12.11. A simple automatic device monitors the quantity of oil in
the circuit. Where a failure occurs in one of the systems it is located and

Proximity switch 'A'
Proximity switch 'B'
Motor Motor

Pump Pump
No. 1 No, 2

Spool valve Spool valve
position when position when
pump operating pump stopped
(for anticlockwise
tiller movement)

Figure 12.11 Ram type twin circuit system—pump 1 running circuit 2 leaking