I had a somewhat amusing experience with my flux gate
compass two weeks ago on a
passage from
Bermuda to
Antigua. To make a long story short we were sailing in light winds with a capable helmsman on watch, with the
autopilot engaged. I decided to
work on a couple things below and had a tool roll out for my
project. As I'm about to start some
work I hear a bit of a panicked "wtf" from above and the
autopilot veers the
boat off suddenly in a new direction; the
wheel spinning quite deliberately. Luckily the helmsman was on the ball, put the AP in standby, grabbed the
wheel and put us right back on course before a bad gybe ruined our day.
Now under control and looking at the chart plotter it thought we were 140 degrees off course. But we weren't. It was a big mystery for a moment until I realized I had unrolled my tool bag on the
cabin sole directly above (maybe 5") where the flux gate
compass is mounted just forward of the
mast, low and central where it belongs. Well that was it. Moving the tools corrected the problem immediately, and putting them back repeated it. Big lesson learned as to the sensitivity of the compass to
interference, and a good story to tell over
rum drinks in the future.
I'll add to this that I upgraded the flux gate last year to a faster more sensitive model than I had, which markedly improved the performance of my autopilot (all
B&G electronics). I wanted the ideal location low and central in the
boat but was worried about
interference, as there's lots of metal objects and
electrical stuff running around down there. I found an app that measured magnetic fields that worked great and gave me confidence in this new location for the compass. I don't seem to have that app anymore, but I see there are quite a few options in the app store. Very useful.
JR
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