I had a somewhat amusing experience with my flux gate compass
two weeks ago on a passage
. 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.