Compass adjustment

[KayakDan]

The compass on my M is way off-like 20o! I know there's some interference,and I know it can be compensated so it will read correctly. Short of moving it to the bulkhead(it's on the pedestal) does anyone know how-where I can get this done?
Compass GPS is fine,but it's no substitute.

[richandlori]

Almost every compass can be adjustedyou can also try and remove the electromagnetic interferences to lesson the error. By make no mistake about it, EVERY compass on a boat will have error and there is no such thing as perfect. Compose a compass deviation table and simply add/subtract the correct amount to make it read properlyor use you GPSwhich is perfect so long as the US Government doesnt turn if off in the event of an emergency or if you sail around a sensitive security zone (like the Nuke Plant in my home port)

[baldbaby2000]

There should be adjustment magnets unless it's a cheap one. Usually the procedure is something like: line the boat up close to magnetic north and south, adjust one set of magnets to the proper reading, then line it up close to magnetic east and west and adjust the other set to the proper reading. Then repeat if needed. Remember you want to use magnetic north and south.

I also like the compass over the GPS because the boat doesn't have to be moving. Besides, the compass is powered by the earth and let's me stay in touch with nature!

[Terry]

I remember when I got my Plastimo hand held compass and proceeded to find a spot to mount the bracket, the pedestal seemed the likely spot. As soon as I put it near the pedestal it started to swing so I tried testing the area with my old Silva hiking compass, same thing, it swung. I decided the wiring and throttle controls in the pedestal was the culprit and then mounted my compass on the bulkhead where I could read it easily or pick it up to take a reading. The hand held does not have adjustments since you can take it in your hand and move it away from magnetic interference. Since my street runs north & south and my driveway east & west it was easy to set it right. Even though some other compasses can be adjusted I have to wonder if the deviation changes when more or less current is flowing through the wires in the pedestal or when the ignition is on or off. I would find a more favourable position than the pedestal to mount it myself.

[baldbaby2000]

Since my street runs north & south and my driveway east & west it was easy to set it right.

Doesn't the metal trailer mess up the readings?

I'm not sure if there's enough electrical current variation near the pedestal to mess up the reading but it's possible. On our Surburban we have a compass suction cupped to the inside of the windshield and it changes a little when the heater fan is turned on.

BB

[richandlori]

. Remember you want to use magnetic north and south.

Just remember...when reading the charts make sure you are aware of the magnetic vs the true readings on the compass rose. You do your Navigation calculations in True readings, then convert to magnetic readings, THEN add you ships compass' deviation to the reading as standard Navigation. So either way...you still want to know you compass' deviation for the 8 points of the compass. (seemy ASA 105 Navigation Class at least taught me something!)