Steel hull boats can cause a magnetic compass to
read incorrectly. A Steel Boat Compass
comes with two spheres, one on each side of the binnacle and they are used to compensate
for the deviation caused by the steel boat hull.
These soft iron quadrantal spheres are used to adjust
and compensate for the steel hull and it may have to be adjusted by a professional
compass adjuster. In some steel boats, flinders bars or heeling
magnets may also be needed to be used to compensate the deviation.
Large changes in latitude effect the deviation of a steel or
iron boat compass. This must be considered when cruising.
When sailing vessels heel out of a horizontal trim, this may
cause a compass to need heeling magnets to reduce their deviation. The heeling magnets
go under the compass. By sailing an N-S heading and maintaining a constant
heading, heel the boat slightly. Place the correction magnet vertically under
the compass so as to ELIMINATE ONLY THE DEVIATION INDUCED BY THE HEELING. If
you cannot make the adjustment, then at least note the difference the heel had on your
compass.
The quadrantal spheres of soft iron are used to compensate the
deviation caused by the iron or steel hull.
Electronic or Fluxgate compasses are subject to the same disturbing
influences as are ordinary compasses, but with electronic compasses the sensor
unit may be remotely located in a position where the bad effects are absent or
minimal. With these units the compensation can be done with magnets or electronically.
A variation can be electronically inserted so that the instrument gives a true
heading. This is one big advantage to a digital compass. A disadvantage is that
it has to have electricity to work.
With a digital compass system, multiple displays are easy.
You can have them both above and below deck, and many need no wiring to connect
them. It is nice to have a Tell-Tail compass below deck.
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