Autopilot Heading Adj

[ign]

My magnetic compass and my autopilot's digital compass show very different readings. I have tried adjusting the digital compass to match the boat's magnetic compass, but when I do this at one heading the variance between the boat's compass and the magnetic on a different heading is also off, often times by as much as 20 degrees.

What is the best way to align the magnetic and the electronic compass?

thanks for any tips,

 

[William_H]

Compass correction

Here is a difficult subject especially if it is on a steel boat.
However assuming you have a fibreglass boat then it can only be external influence that is causing errors.
Firstly you need to zero the correction on the a/p compass and find out which compass is correct on all headings.
A simple crude way to check compass is to use a hand bearing compass. Get someone in a dinghy towed behind to give actual heading of the boat on the various headings. Or a person sitting on the stern rail may be sufficiently far from other influences to get an accurate reading.
Once you find which compass is correct then you can look for external influences. Radios and especially loud speakers or analogue meters have strong magnets which can cause errors.Large masses of iron like an engine can also give some influence. The sensor for the a/p may be located away from the main equipment so it may be possible to move it if you have an error.
Something I never thought of at firstr is where an engine is under a compass. The influence can be different if the boat is on a heel. ie the engine is under the compass when flat but either to the left or right of under the compass when heeled over.
Ultimately you may need to fit a correction card for all compass headings for one or both compasses.
As a matter of interest an aircraft will have its compass (es) checked for error min. every 3 years.(a correction card is usually fitted.)(on single engined aircraft also each time engine is changed or overhauled or any new radios fitted)
I guess compass accuracy is not so critical with GPS continually checking location. So you may just have to accept errors. good luck olewill

 

[simonfraser]

i took the compass out of my tiller pilot and mounted it well away from the outboard, much better result.
but, you may just want to live with the course holding ability of the pilot and use other means to navigate.

 

[pampas]

Start your auto helm as if it was a brand new one, wait for slack water,away from traffic and go into set-up and do to circles at constant speed , should read ok then, Have you done this recently?

 

[ign]

Haven't tried this last option and understand it works for other electronic compasses. Also, I think the compass may be getting interferrence from some tools stowed near by.

thanks for the suggestions!

 

[Alcyone]

We did this last weekend with a Raymarine. You had to enter calibration mode, turn in a slow circle for 3 minutes and then you were given an adjustment figure. The detailed instructions were in the manual, which I think is available online, if that helps.