Jeff wrote in :

Sounds to me like you have a boatload of people who have forgotten how
to use a compass, if they ever knew.



You mean that big round thingy we moved out of the way to install the radar
display that bobs around and spins crazy when the waves slap the hull?
What kind of reading can you get from something swinging 30 degrees off
course?

Just kidding. It's there and we use it, sort of. Over time, we made up a
compass correction chart for it using the chartplotter headings and compass
readings. The chart looks like a big sinewave. The compass reads
correctly at 2 points where the chart crosses zero. Otherwise, it's off by
as much as 13 degrees at two other points at the peaks. Totally disabling
DC currents has no effect. I have all the wiring as far from it as
practical. There's no close magnetic objects, either. All the electronics
is plastic with copper circuit boards. We tried to compensate it out with
the compensating adjustments and this chart is the result of the "best
setting" of those magnets.

Try that with your compass. Chart its error against the GPS headings over
time as you sail and plot it on a line chart. I was amazed how far off it
is. Sure glad we don't use it for NAVIGATION!....(C;