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Old 04-12-2007, 03:14   #16
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hi, I'm just about to buy an elite which will need all instruments replacing and probably boat re-wired/new batteries/ battery management system/ charger / mains electric panel etc, any suggestions re electronic management systems appreciated, I'm in UK but jobs will be done in France
Time is of the moment
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Old 04-12-2007, 06:52   #17
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You can make a magnetic shield with mu-metal foil (nickel-iron) - google for info. The material is available from McMaster-Carr and elsewhere...

Cheers,
Steve
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Old 04-12-2007, 10:00   #18
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Magnetic fields and EMF are being confused. They are very different in how they affect a compass. Lead will stop EMF but not a steady magnetic field such as the Earths magnetic field. DC currents create steady magnetic fields, which will destroy a compasses accuracy and lead will not stop it. Besides, if lead really did stop a steady magnetic field then why would you want to put it anywhere near a compass? Only ferrous metals affect steady magnetic fields.

A deviation card is considered no good if it generally has any corrections above 15 degrees or so. This is what I have been told by compass adjusters as far as the Coasties are concerned. I have seen compasses swing over 30 degrees when exposed to DC caused magnetic fields making any sort of deviation card worthless. Really the best thing is to get a standard compass and have a professional make the adjustment and create a deviation table for you. You can then put the steering compass where ever you want and you won't have to worry about inaccuracies. You can then make a second deviation table for the differences between the steering and standard compasses.

You can find a better and more detailed explanation in Bowditch.
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Old 04-12-2007, 10:29   #19
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One more related thing: If you absolutely have to run DC wires near a magnetic compass then twist the pos and neg wires tightly together. This will partially attenuate the fields (cancel out the opposite magnetic fields) generated by each wire.
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