Seiwa SW AP01 - Manual (Page 10)

The action of the rate or counter-rudder during a turn is illustrated in Fig 1.3. Generally,
when the rate component is increased, vessels hold a course better but react to changes in
the reference course more slowly. Counter-rudder also improves control for most vessels
operating in a following sea.
REFERENCE
COURSE
NORMAL RUDDER
NEUTRAL RUDDER
COUNTER RUDDER
Figure 1.3 Rudder action during a turn in the RATE mode.
Autotrim
Vessels often show a steering bias or offset, which can be due to weather, propeller torque
or towing a load off-centre. The autopilot responds to this by progressively trimming the
centre position of the rudder until the average heading of the vessel equals the reference
course.
1.1.3 POWER STEERING
Since the autopilot controls a power steering system, options are available to use this to
steer the vessel by hand while away from the main wheel. This can be done by a hand-held
device on a cable or a permanently mounted second steering station.
1.1.4 OPTIONS 9
An autopilot commonly uses a fluxgate compass for its heading measurement. Such
compasses, though effective, suffer from acceleration errors and a very effective way to
reduce these errors is to combine a fluxgate with a rate-of-turn gyro. A further option is to fit
a pickup device (slave) on the ship’s compass and take advantage of its dynamic
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