ComNav Commander P2 & P2VS Installation & Operation Installation
Document PN 29010074 V4.1 - 50 -
Magnetic Compass and Sensor
The ComNav Magnetic Sensor can be mounted to ComNav’s standard Magnetic
Compasses, and also to a wide variety of other brands of externally-gimballed compasses.
Caution! The Magnetic Sensor MUST NOT be attached to an internally
gimballed compass (that is, where the compass card is gimballed and the
bowl of the compass is not).
Doing so will result in large errors between the compass and the autopilot. This
is because the compass card does not remain parallel to the sensor when the
boat rolls or pitches.
Locate and mount the compass in a position that minimizes magnetic interference. The
compass should be at least 1 metre [about 3’] away from such equipment as radios, radars,
depth sounders, and engine instruments.
To reduce the possibility of the card ‘tumbling’ in rough weather, mount the compass as close
as practical to the center of pitch and roll. Mounting the compass far forward under a bunk or
similar location is a poor choice for rough weather performance.
Important! Always keep in mind that the compass is the single most vital part of an
autopilot system. Locating a Magnetic Compass properly, particularly on
steel-hulled boats, is essential to ensure proper operation of the autopilot.
ComNav strongly recommends that the services of a qualified compass adjuster
be used to select the best installation location, and to compensate the compass
properly for deviation, including that caused by heeling error.
Care must be taken not to place compensating magnets too close to the
compass, as this will cause the Compass Sensor, mounted underneath the
compass, to read incorrectly. To correct compass deviation on steel boats, or on
other boats with magnetic compensation problems (typically caused by
interference from adjacent ferrous masses such as an engine block or winches),
the use of a pair of compensating quadrantal spheres is recommended.
The Sensor can be mounted to the bottom of the compass using the brass screw supplied, or
it may be bonded directly to the compass bowl using a suitable adhesive. The Nylon Washer
should be placed between the Compass Sensor and the bottom of the compass bowl.
Check to see that the Senor’s brass screw does not touch anything when the compass bowl
gimbals – e.g., a reservoir for the compass’ damping fluid
With the Sensor mounted to the bottom of the bowl, the magnetic compass may be used as a
steering compass, if desired.
It is also possible to mount the Sensor above the compass. This reduces the possibility of
interference from the compensating magnets, but also reduces the visibility of the compass.
Optimum positioning of the sensor can only be accomplished once the Autopilot system has
been installed and powered up, during the Compass setup procedures (see page 93 in the
Setup Procedures
section of the manual).
Electrical Connection
Route the Magnetic Compass Sensor cable from the Compass to the location where the SPU
will be.
Ensure that there is sufficient slack in the cable to allow the compass bowl to tilt and rotate
freely in all directions.
See
Compasses
on page 66 for further details on connecting the cable to the SPU.
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