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2.5 Tiller Movement (Gain)
The Tillerpilot will apply adjustments to the tiller in
order to compensate for heading variations, the amount
of movement being proportional to the heading error
detected by the compass unit. The amount of move-
ment is set by the Gain (sometimes referred to as the
rudder ratio).
The Gain setting can be likened to driving a car - at high
speeds, very little wheel movement is necessary to steer
the car (LOW gain). When driving at slow speeds, more
wheel movement is necessary (HIGH gain).
Fig 2.6A shows the effect of setting the Gain too low: the
vessel takes a long time to return to the correct heading.
Fig 2.6B shows the ideal setting, where errors are quick-
ly corrected. Fig 2.6C illustrates the effects of setting the
Gain too high, which causes the vessel to oscillate
around the correct heading. Excessive Gain (Fig 2.6D)
creates a tendency to instability of course, leading to
increasing error.
The Gain setting can be adjusted manually - see section
4.2. Additionally, if Speed data is available via NMEA,
the Tillerpilot will automatically optimise the Gain
within the manually set value.
2.6 Seastate
In rough weather, more variations in heading will be detected by the Tillerpilot due to the heavy
seas yawing the vessel. If no account of this was taken, then the Tillerpilot would be overworked,
causing unnecessary strain on the unit and excessive drain on the batteries. The Tillerpilot will
continuously monitor corrections applied to the tiller over the course of a voyage, and allow a
“dead band” within which the boat can go off course without corrections being made. The dead
band is automatically set and updated by the Tillerpilot to give the best compromise between
course holding and battery consumption. However, this can be manually set if so desired. To man-
ually adjust the Seastate, please refer to section 4.4.
2.7 Autotrim
Under differing conditions a tiller bias (sometimes known as standing helm or rudder trim) is
applied in order to steer a straight course. An example is when sailing close hauled where the ves-
sel will normally pull into the wind, and the helmsman applies a standing helm to leeward in order
to maintain course. The amount of this standing helm varies according to factors such as strength
of wind, boat speed, sail trim and amount of sail set. If no account of these were taken, then the
vessel would tend to veer off course, or pull round head to wind if sailing close hauled.
The Tillerpilot continuously monitors the average course error and applies a bias to the tiller to
compensate until the optimum condition is reached. This bias or standing helm is applied gradu-
ally, so as not to upset the normal performance of the Tillerpilot. Thus, it may take up to a minute
or so to fully compensate after changing tack. Once optimum trim is reached, the pilot will still
monitor for changes in the prevailing conditions and update the trim accordingly.
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