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January/February 2018 Marine Electronics Journal 49
ran with outboards. Linear rudder senders
are used for applications where a rotary unit
is not feasible.
Sensor location is critical
The rudder sensor requires near perfect
geometry to function properly. Since steering
systems vary greatly, there are many configurations that are used, but an even, linear
response both port and starboard is desirable.
This means that the physical mounting of the
sensor is critical and can be challenging.
Improperly mounted or configured rudder
sensors may cause the pilot to steer differently
to port and starboard, which is disastrous for
pilot performance. A typical rotary rudder
sensor should show a rectangle at midship
and a parallelogram at all rudder positions,
hard over to hard over. The AMEI class
teaches autopilot installation techniques.
A basic autopilot includes a compass and
a rudder sensor. When turned on and
engaged, the pilot tries to keep the heading
steady as she goes. When the boat wanders off
course, a heading error is generated and then
corrected by applying rudder opposite the
heading error. Once the error is eliminated
and the boat is back on course, counter rudder is applied to stop the turn. This most
basic pilot function requires an accurate and
responsive compass and rudder sensor. Calibration of the rudder sensor, setting limits
and center are normally required. Compass
calibration to compensate for deviations is
also usually required. The physical planning
of the installation can make all the difference.
Perfect geometry on the rudder sensor, good
compass location—these things matter.
Poorly installed equipment may appear to
work, but will not perform in adverse conditions.
Autopilots are prone to failure, subject to
wildly varying conditions and they use a lot of
juice. This popular accessory helps with operator fatigue but introduces a level of danger
because of potential failures and operator
complacency. Today’s pilots have alarms to
warn the operator of failures and errors such
as Off Course, Compass Failure, etc. As long
as the operator sees the alarm and reacts to it
appropriately, alarms are a big safety addition.
Since autopilots are complex with many
modes, training the user is imperative. There
is no substitute for eyes through glass, an
actual human watch-stander. Just because the
autopilot steers for you, doesn’t mean you can
take a nap!
Next month we will take a wider look at troubleshooting. Complex devices, like autopilots
require a level of knowledge and proper techniques to diagnose failures. This type of knowledge typically cannot be taught in a classroom.
There are some tricks and methods that can help
troubleshooting any complex system.
Proper mounting of rudder sensors is critical for autopilots to steer correctly. A rotary rudder installation should resemble a rectangle at midship and a parallelogram at all rudder positions, hard over to
hard over. Credit: AMEI course materials