Is it possible to shield the compass for an auto-pilot?

Discussion in 'OnBoard Electronics & Controls' started by sportfisher, Aug 19, 2009.

  1. sportfisher
    Joined: Aug 2007
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    Location: New york

    sportfisher Junior Member

    I recently purchased a used 2004 27' Center Console. The boat came with a Ray Marine ST6001 auto-pilot. I calibrated the compass according to the units owner’s manual. I cannot get the auto pilots compass deviation better than 30 deg. The compass for the auto pilot is located in the inside of the console and against the most forward wall. It is about 4' - 5' from any electronics and about 3' to 4' from the batteries. It is right next to the electric head.
    I'm assuming there is something interfering with the compass and not something wrong with it.
    Is there any way I can shield the compass from ferrous metals. If shielding is not an option, does anyone have a suggestion for a new location?
     
  2. TerryKing
    Joined: Feb 2007
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    Location: Topsham, Vermont

    TerryKing On The Water SOON

    You need to find what is causing the extra magnetic field near your autopilot.

    Start with a handheld compass, such as for hiking. Hold it as far above the location as possible to determine the unaffected indication. Now start right at the autopilot location. How much is it deflected? Start moving it around and quite close to metal objects to find out what might be affecting the autopilot.

    I'd bet that you'll get a big deflection near the motor on the head...

    Current-carrying wires will also have a field. Totally disconnect the battery, and then check the same location with the battery connected.

    I've heard stories of autopilots that steered differently as electric winches were operated.

    Shielding: You obviously don't want to shield the autopilot which is looking for the earth's magnetic field! Shielding the SOURCE of a magnetic field is possible. Steel sheet of perhaps .050 inches is a start. Multiple layers with insulating material in between are sometimes used. More complex multilayer shielding (google "mu metal" ) is possible but not cheap.

    I'd use the hand compass to find a good relocation prospect. Check any location again with the boat yawed 90 degrees: you MIGHT have been on a bearing where effects cancelled out..

    And let us know what you find...
     
  3. Luckless
    Joined: Mar 2009
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    Location: PEI, Canada

    Luckless Senior Member

    My first thought is, can you get somewhere fairly clear of power lines, running engines, and large amounts of iron? (like a field) that you can work out detailed bearings from a map, and be sure the unit is functioning properly away from the boat.

    No sense chasing EM emissions around your boat if the unit is half dead already.
     
  4. Fanie
    Joined: Oct 2007
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    Location: Colonial "Sick Africa"

    Fanie Fanie

    If it is magnetism causing the problem then you can shield it off.

    http://www.lessemf.com/mag-shld.html

    You will typically need the MagnetShield product, they have a description there somewhere on how to shield magnets. It sounds like it is the electric head you will want to shield.

    Couldn't find a shop closer to home ;)
     

  5. sportfisher
    Joined: Aug 2007
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    Location: New york

    sportfisher Junior Member

    Thank you for the reply. I'm going to take a hand held compass and compare a few different readings. I'll let you know what I come up with.
     
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