ComNav 1101 Autopilot INSTALLATION 4 - 13
Plug the end of the Fluxgate Compass cable into the “COMPASS”
receptacle on the SPU. If the 12m (40') cable is too short, plug-in
Compass Extension Cables are available in various lengths from
your ComNav dealer. Cutting and splicing the Fluxgate Compass
cable is NOT recommended.
Note: Because of the sensitivity of Fluxgate Compasses to the
earth’s vertical magnetic field, it is recommended that a Heading
Rate Stabilizer be added to the compass at latitudes greater than
50 degrees north or south. Consult the factory for special
instructions for mounting Fluxgate Compasses and Heading Rate
Stabilizers on steel vessels.
Magnetic Compasses
The advantage of using a Magnetic Compass with a Magnetic
Compass Sensor attached to it is that the Autopilot is sensing the
position of the magnets on the compass card rather than sensing
the earth’s magnetic field directly.
Since the card of the compass has physical inertia, it does not
react immediately to the changes in the magnetic field it is
immersed in, but only to those changes which persist long enough
to overcome the resistance of the compass card to movement.
This means that the compass is a more stable heading reference
than a Fluxgate Compass. The Magnetic Compass will largely ignore
changes in the magnetic field in the plane of the compass card
caused by vessel motion to which the Fluxgate Compass may react.
This is particularly important in high latitudes, (such as Alaska,
Labrador or the North Sea), where the horizontal component of the
earth’s magnetic field (which is the portion that the compass is
trying to detect) is very small relative to the magnetic field of the
vessel.
The disadvantage of the Magnetic Compass is that in very rough
weather with the vessel going to windward, it is possible for the
vessel motion to upset or “tumble” the compass card, disabling
the Autopilot.
Because of the relative insensitivity of the Magnetic Compass to
both the earth’s and the vessel’s vertical magnetic fields, (due to
its inertia), it is recommended for use at latitudes higher than 50
degrees (north or south), and for use on steel vessels when
optional quadrantal spheres are included.
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