Autopilot Losing It's Way !

[rebel heart]

Originally Posted by colemj

His boat is a 50' Simonis catamaran. No windvane could possibly steer that boat for many reasons.

Mark

Yeah sorry, I only know about properly sized monohulls.

[colemj]

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...

Mark

[Ex-Calif]

Originally Posted by colemj

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...

Mark

When I went to mechanic school (a couple of moons ago) one project was to take a box of parts (ultimately the box had incorrect and too many parts) select the correct parts and asssemble and rig all the parts of a remote fluxgate compass. Then calibrate the compass. When you had it right you brought the instructor over to check your fluxgate project. Of course the instructor carried a nice big magnet in his lab coat for this part. Caught more than a few aspiring mechanics.

[Opie91]

I had a similar problem moving a power boat for a friend from Norfolk, VA to CT. We were cruising along just fine with the autopilot on in fairly rough conditions when suddenly the boat turned 90 deg to port.

Long story short the guy who installed the autopilot mounted the flux sensor on a piece of insulation board. One good wave and it fell off the wall.

One thing, compare your autopilot heading indication to your compass. If there is a big split, suspect an issue with the fluxgate sensor.