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post #1 of 6 Old 05-18-2019 Thread Starter
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Magnetic interference from mast affecting AP?

Ok. Before I waste a whole bunch of time troubleshooting I figured I ask if anyone every saw something similiar.

I have a CPT autopilot that last year was working awesomely. I went to use it this year (first trip of the year) and it's all screwy now.The only change from last year is that I have my mast down as I will be transiting the Erie canal shortly. It's strapped on deck.

Is it possible the mast is interfering to the point my autopilot doesn't work? The CPT's compass is in the control unit directly. I've tried moving it into every position I could reach in the cockpit and everywhere gives the same result. As soon as I turn on the "hold heading", it turns hard to port (like a good 1/4 turn of the steering wheel), and then keeps turning the wheel every second further to port until I'm clearly driving in a circle.

It will be a long trip if I can't use my autopilot :O

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post #2 of 6 Old 05-18-2019
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Re: Magnetic interference from mast affecting AP?

first? is your mast steel? if so then yes it is affecting the AP. type of boat might be helpful is it a steel hull? have you tried using a hand held compass to see if you have a magnetic field that is affecting the AP


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post #3 of 6 Old 05-19-2019
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Re: Magnetic interference from mast affecting AP?

I would be surprised if your mast itself is made of any sort of ferrous iron. If aluminum, that would not interfere with the compass. Of course, any stainless steel bits might.

Generally, magnetic interference would cause the AP compass to be wrong, but typically consistently wrong and not necessarily cause a constant turn. Nevertheless, APs don't always work on magnetics alone and there could be other interference. Indeed, there could be another problem altogether.

Would it be too difficult to lift the mast off the deck and test it again? Unfortunately, electronics going screwy over the winter is SOP. Sometimes it's just corroded connections that get worse as metal contracts in the colder temps.

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post #4 of 6 Old 05-19-2019 Thread Starter
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Re: Magnetic interference from mast affecting AP?

Sorry, guess I should have mentioned that. Mast is Aluminum, though standing rigging is steel. I checked with a compass and I can't find any deviation anywhere in the cockpit (aside from relatively close the the ship's main compass, as that's a magnet :P)

I'll try calling CPT tomorrow and see what they say. Thanks!
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post #5 of 6 Old 05-20-2019
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Re: Magnetic interference from mast affecting AP?

Most of the steel on your mast is likely to be some type of austinitic stainless. Austinitc stainless steel is generally not magnetic and unlikely to cause this problem.
Many auto pilots do a find zero motion when you start them up. It sounds like the auto pilot is not sensing the zero point so it keeps turning. My guess is a mechanical problem with how the unit senses position inside the drive unit and not a compass problem at all.
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post #6 of 6 Old 05-20-2019
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Re: Magnetic interference from mast affecting AP?

I'm not familiar with CPT autopilots, but do you ever have to calibrate or "swing" its compass? We experienced a similar problem with our Raymarine authohelm. It would turn hard to port and just go in circles. We fixed it by re-calibrating the compass.
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