Wrong Way Corrigan

kas919

kas919

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Joined
Dec 9, 2025
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Age
62
Location
Venice, FL
Model
Freedom 285
I rarely get out of site of land, but I am noticing that my Garmin MFD and my Ritchie Compass are not reading the same heading. I would say it may be off as much as +/- 20 deg. I was thinking the other day that I should probably figure out who to believe. Of course we all assume that GPS is never wrong right? Should I have the compass professionally calibrated? Any thoughts or wisdom would be greatly appreciated. Thanks
 
Depending on the model of your compass, there could be adjustment screws on it.
 
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First check to see if you have your Garmin set to read "magnetic" as opposed to "true north".

Second... do you have any speakers/etc (sources of magnetic disturbance) close to the compass?

With the boat in your slip, does turning the wheel affect the compass? Does using/turning on any nearby electronics affect the compass?

The, yes, follow the compensation procedure (plenty of info out there about this). Look for two brass (usually brass) screws on the back side. This is a normal thing to be done based on where someone boats.
 
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Based on the OP location, the declination would be about 10 degrees so that doesn't explain the 20 degree difference.

One simple test for magnetic interference is to turn off all battery switches and note the compass heading. Not turn on the battery switches, note the heading again. Turn on things one at a time and look for changes, Don't forget the stereo if you have one, especially if there are speakers mounted close to the compass.
The above test will test for electromagnetic interference, the speakers can cause both magnetic and electro magnetic interference.
Phone chargers, magcase phones, magnetic mounts, heavy current cables and the like are all possible sources
It could be adjustment as noted but test for magnetic and electromagnetic interference first
 
When you are traveling in a channel and your chart shows you in the channel, the GPS is correct.
When you are offshore and you see Venice to the east on your chart and your track takes you back to the inlet, the Garmin is correct.

Compasses are notoriously inaccurate due to things that Dennis mentioned and the declination in venice Fl is about 8 degrees west

I never use a compass anymore. Your Chart allows you to see where you are going and where you've been vs pointing in a direction and trying to watch a compass and drive.
I wouldn't spend time or money trying to make a compass "correct" but yes you should figure out if there is something nearby effecting it.

You probably have a compass on your smartphone you can compare to.
 
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