A The value is set too high. Steering becomes unstable and often the overshoot will
increase
B The value is set too low. It will take a long time to compensate for a heading error,
and the autopilot will fail to keep a steady course
Counter rudder
Counter rudder is the amount of counteracting (opposite) rudder applied to stop the turn at
the end of a major course change. The settings depend on vessel’s characteristics, inertia, hull
shape and rudder efficiency.
• If the vessel has good dynamic stability, a relatively small value will be sufficient
• An unstable vessel will require high value
• The greater the vessel’s inertia, the greater value will be required
Increasing counter rudder value may result in some higher rudder activity also when steering
a straight course, particularly in high waves.
The best way of checking the value of the Counter rudder setting is when making turns. The
figures illustrate the effects of various Counter Rudder settings.
A Counter rudder value too low; overshoot response
B Counter rudder value is too high; sluggish and creeping response
C Correct setting of Counter rudder; ideal response
Perform various course changes and observe how the boat settles on the new heading. Start
with small changes, 10-20 degrees, and proceed with bigger changes, 60-90 degrees. Adjust
Counter rudder value to obtain best possible response as in illustration C.
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Note: As many boats turns differently to port versus starboard (due to propeller rotation
direction), do the course changes in both directions. You may end up with a
compromise setting of Counter rudder that gives a little overshoot to one side and a bit
creeping response to the other.
Autotrim
Controls how fast the autopilot will apply rudder to compensate for a constant heading
offset, e.g. when external forces such as wind or current affects the heading. Lower autotrim
will give faster elimination of a constant heading offset
32
Work profiles| AP70 MK2 Operator Manual
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