Seiwa SW AP03 - Manual (Page 10)

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
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
performance and the fact that it has been magnetically compensated. Alternatively, this
autopilot may take its heading in digital form from a ship’s gyro or other electronic heading
sensor. The autopilot has built-in facilities for automatic or manual compass calibration.
When connected into an NMEA data system, the autopilot can receive navigation data, as
mentioned above or wind direction data. Some of this data, which is not used for autopilot
operation, is displayed on the autopilot screen for convenience. The autopilot generates
output data containing the current heading, which can be fed into an instrument or radar
system.
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