We were doing a 6-day passage
with a friend. A couple times each day, the autopilot
would just do a Crazy Ivan and run way off course suddenly. For 3 days, I couldn't figure this out - ran down wiring
, voltage, etc. Then it occurred to me that it never happened when our friend was on watch - and, in fact, it always seemed to happen when he went below for rest.
Sure enough, shortly after he took his next rest period we had a crazy Ivan. So I went down and asked him if he had done anything or moved anything. He said no - just put some of his clothing
in a drawer and took a nap.
So I opened the small drawer and the boat immediately did another crazy Ivan. In the drawer was his metal-ribbed back brace for a back condition we didn't know about.
The drawer right above the fluxgate compass