A cautionary tale.

[Norman_E]

A bit of a cautionary tale.
I sailed from Marmaris to Bozukale Bay yesterday. It was the first sail this year and started in about 2 knots of wind, and ended docking the boat at Sailors House in 20 knots. After leaving the Marmaris inner harbour I switched on the Simrad Robertson AP11 autopilot and after motoring straight for a short distance the boat started a turn to port which had me rushing back to the helm to correct it. I reset the autopilot and after a short while it started a turn to starboard, which was when I noticed that the autopilot was showing a course of 300 degrees, when our actual course was 155 degrees.

My first thought was that the fluxgate compass needed calibration, which is achieved by going into the autopilot menus and then slowly turning the boat in circles. I did that with no good result and then the penny dropped. In the winter I had changed a pump in the waste system and put the old but still serviceable one into a locker. Of course the old pump was one with a heavy steel case and I had put it in the locker where the fluxgate compass is fitted. All was well once I removed it, so the moral is be careful where you stow things.

 

[prv]

Probably had magnets in the pump motor as well, just to make things worse

I had a similar experience when my dad stowed a 4-pack of Fosters in steel tins hard up against the compass. I later moved the compass to a position inside the cabin table structure where it should be safer from having things stowed against it.

Pete

 

[Fenders]

Also happened to me when I had tidied up my locker. When I next went sailing the boat was rolling about a tad and the spare gas bottle had slid on the plywood floor jamming itself against the flux gate.
Took a while to discover the problem but as soon as the gas bottle was removed all systems returned to normal.

 

[colind3782]

I found a similar problem when I used to keep my two phones in a handy tray on the helm pedestal. Moved the phones, no more problem.

 

[bigwow]

Probably had magnets in the pump motor as well, just to make things worse

I had a similar experience when my dad stowed a 4-pack of Fosters in steel tins hard up against the compass. I later moved the compass to a position inside the cabin table structure where it should be safer from having things stowed against it.

Pete

Would it not have been easier to drink the Fosters than move the compass?

 

[savageseadog]

We have a B&G electronic compass on our Hydra 2000 system it's always been reliable and accurate. One race we were on it was noticed the reading was about 10 degrees out, I assumed the worst until we got into port and realised my bag had a small radio in it fitted with a speaker about 0.5m away from the sensor. The magnet had indeed deflected the reading.