Too close?

[doc g]

Navigate to a waypoint instead of a compass heading. ........Pat

[Captain Ralph]

The later flux-gate compasses can be calibrated. A special program helps them make a real 360 degree swing. Check your owners manual.
I remember working on older APs like Benmar, a real compass with spokes in the card that an optical eye would read. No calibration on these beast.
Other mfg's used this style and some are still in service.

I have also chased later compass issues when mounted close to bilge, sump and black water pumps.
I remember an engine alternator driving one compass crazy at different speeds.

The best horror story; compass installed in the bottom of a state room closet. All was good till suddenly one weekend the AP went crazy; Found steel toed shoes in there also.

What model AP do you have?
Find the compass and survey the area well. Could be a tool box close by.

[SeaEric]

Did I miss the comment that says what brand the A/P is? If it's a Garmin, I own one and have some related experience.

[oscarvan]

Yep, late model Garmin.

[bigbill]

is the garmin networked with other stuff through a nmea 2000 backbone? mine had similar problems until i put a terminator plug on the backbone. check to see if you have a terminator

[SeaEric]

The compass for the Garmin AP that I have is about the size of a tennis ball. We had all sorts of trial and error before we found a good location which ended up being low in the port side hanging locker in the aft stateroom. We tried various locations as suggested by the Garmin install instructions. At one point we thought we had it, but while underway it would unexpectedly veer off - often when I was doing an engineroom check. it turned out that the 12v DC lighting had a major effect on the compass. Turning the DC engineroom lights on caused mayhem. The small hand held compass was a big help in the search. One more thing: When I purchased the AP Garmin said that the "Rudder Feedback Sensor" was optional. It's not. Without it we couldn't get the unit to work properly. With it added (plug and play) no problem. it also adds the rudder angle indicator to the Garmin display, which is nice to have.

[racclarkson@gmail.com]

Exactly. Go back to Post #5. It can be the most insignificant combination that causes the swing. And your description is exactly in line with my experience aboard Aslan.

[oscarvan]

Thanks all for the excellent suggestions. I will now find the tennis ball and follow the suggestion in post #5.

[Boatsb]

Which model garmin?

The "tennis ball" is older technology. The last 2 or 3 models don't use it.

[wallison]

When installing the Clear Cruise system I used a magnetometer iPhone app called iNstall from Gemeco. The app (recommended by Raymarine) is free, worked like a charm and will tell you how much RMI there is, and whether it’s a problem.