STEERING GEARS

157

STEERING GEARS

The simplest form of lever for turning a rudder is the "helm," now
known as the "tiller" in small boats. A wheel and axle purchase i&
substituted in small ships in order to
get more power to turn the heavier
rudder. It is simply a rope with its
middle part wound round a barrel and
the ends led through leading blocks at
the side of the deck and made fast to the
end of the tiller. The steering wheel is on
the end of the barrel and when the wheel
is turned the barrel with the rope on it is
turned also and the rope pulls the tiller to
one side or the other.

The figure shows a type of screw steering
gear fitted in larger vessels A crosshead A
is keyed firmly to the rudder head B, the
crosshead is equivalent to the tiller because
when it is turned the rudder post turns.
C and C are the port and starboard rods,
the port rod has one end bolted to the
crosshead at A and the other end to a
sleeve Dl. The starboard rod is similarly
connected to the crosshead and to the sleeve
JD2. The sleeves Dl and D2 work, respec-
tively, in right and left-handed screws cut
on the common shaft JP, which is turned by
the steering wheel, so that the sleeves
move in opposite directions and turn the
crosshead.

The Requirements of a steering gear are,
to move the rudder to any position with as

Fig. 22.—Principle of the
Screw Steering Gear.

The crosshead (equivalent

Of tiller),
little delay as possible; to hold the rudder B. Rudder head.

t , -i * i • C. Connecting1 rods.

in position under the stresses imposed in Dt sleeves ^working on guide

manoeuvring the ship; to give way before
any abnormal stress such as caused by a
^uve, and automatically to return to its
former position; to be absolutely reliable.
Usually eight turns of the steam steering
wheel are require^ to put the rudder from

rods
Gears with right handed
thread and Z>* with left
handed thread, both
threads being cut on
shaft F, which is oper-
ated in either direction
by hand wheel or engine.