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    Re: Lightning Strike Damage To Navigation Equipment
    From: Bill Morris
    Date: 2015 Mar 10, 21:24 -0700

    I wonder if I understand this correctly?

    When a boat is struck by lightning, many millions of volts and quite a lot of amps flow through various conductors in the boat to earth (or is it from earth?).

    This pulse of direct current causes a pulse of magnetism which induces current in conductors such as those in electronic circuits nearby the original current path.

    As these are used to a diet of only a few volts and they get many more, they die.

    The pulse, having a beginning and an end also radiates in the radio spectrum, which is why lightning (and switching the light on and off) causes scratchy noises on the radio.

    Iff I have understood the matter correctly, then a sextant should survive unless it is in the path of the original current, except perhaps for its lighting circuit. It is less clear that a mechanical chronometer would be unscathed if it has a steel balance spring, which could conceivably become magnetised. I once accidentally magnetised such a spring, with an immediate and large change in the rate of the chronometer. Needless to say, quartz chronometers and wrist watches are at risk as they contain low voltage electronic circuits. A modern mechanical wrist watch is likely to have a "non-magnetic" nickel steel balance spring such as Elinvar, but who knows how it might behave with very large pulses of magnetism. Does anyone own an MRI scanner? I have a mechanical watch I would be prepared to sacrifice for the good of NavList.

    Bill Morris

    Pukenui

    New Zealand

       
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