Magnetic compass affected by electronics/instruments

Discussion in 'OnBoard Electronics & Controls' started by mordenviking, Jul 11, 2017.

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  1. mordenviking
    Joined: Jul 2017
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    Location: Denmark

    mordenviking New Member

    Hello guys
    hope you can help.
    Got my first boat back in march. I was out sailing 220nm a week ago just to test the boat, so i knew what to be fixed and got to learn her in different weather conditions. I noticed that the magnetic compass installed (silva compass 70) had some serious deviation problems, it was around 30-35 degrees off. I noticed it when I need to sail a course 035 but instead it showed that i sailed a course directly north.
    with the silva compass 70 it's also possibly to take it out of the holder and take a bearing, so i took the compass out and moved it to the other side of the boat and then it showed what should be the correct course.
    Is there a way to isolate the compass so it won't be affected by the electronics so it will show the correct course? i rather not move it other side, because i would like to have as few holes in the ship as possible. And no it isn't possible to calibrate the compass with magnets.
    Hope you guys can help
    Thanks :)
    Modernviking
     
    mordenviking, Jul 11, 2017
    #1
  2. hoytedow
    Joined: Sep 2009
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    hoytedow Carbon Based Life Form

    Welcome. Single wire carrying electric current develops a magnetic field. Double wire carrying equal current in both directions cancels out the magnetism. Could the single wire scenario be affecting your magnetic compass? You may be able to fix the problem by adjusting the wiring harness to balance the magnetism.
     
    hoytedow, Jul 11, 2017
    #2
  3. hoytedow
    Joined: Sep 2009
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    hoytedow Carbon Based Life Form

    hoytedow, Jul 11, 2017
    #3
  4. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    Using twisted pairs of wire cancels most of the magnetic field. However, the wiring should be as far as possible from the compass.
     
    gonzo, Jul 13, 2017
    #4
  5. CDK
    Joined: Aug 2007
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    CDK retired engineer

    Of course you can compensate any magnetic compass by placing one or more small magnets in its vicinity, but with a deviation of 35 degrees even a compass with built in compensation cannot be adjusted in all directions. First of all you must find out where the magnetic field originates. It may be an electrical conductor, an external noise filter in the supply line of an electronic device or a large steel object that for some reason has been magnetized.
     
    CDK, Jul 13, 2017
    #5

  7. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    Does the deviation change if you turn circuits on and off?
     
    gonzo, Jul 13, 2017
    #6
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