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    Re: Lightning Strikes: Real Threat or Urban Legend
    From: Lu Abel
    Date: 2015 Feb 15, 00:04 +0000
    There are several ways lightning can damage on-board electronics.

    First of all, a boat's VHF antenna is likely to be the highest point on board and, since lightning is looking for the shortest path to the seawater, it's a prime target.  Many boating publications suggest disconnecting a VHF radio from its antenna at the first sign of a lightning storm -- otherwise it's sure to get fried.

    Except for radar, other electronics on a boat are likely not connected to anything outside the cabin (and above the waterline) and so are unlikely to receive a direct lightning strike.   Even so, a pulse of lighting traveling down a VHF antenna wire may induce a high voltage in adjacent metal.   So there have been cases reported of part or the entirety of a suite of electronics whose wiring ran near an antenna cable being wiped out by a lightning strike even though none of the electronics were connected to the antenna.

    As far as GPS is concerned, I believe there is a low probability of it being affected with one possible exception -- if I have my GPS connected to a VHF radio with Digital Selective Calling, a lightning strike that affects the radio could go up the wires to the GPS.

    If I were going offshore, I'd carry a sextant because it is nice to have an alternative way of determining my position.   But I'd buy an inexpensive plastic one (say a Davis Mark 15), and I'd spend the savings vs an expensive metal one on several spare GPSs -- which I'd keep wrapped in metallic foil and then sealed in a waterproof bag in the bilge of my boat so they would not be affected by a lightning strike on the boat.  

    BTW, I believe I read somewhere that one in every 10 boats in Florida is struck by lightning every year.  So I suspect that insurance companies have a lot of data on the likelihood of damage from a strike and what form(s) it takes.

    From: Doug MacPherson <NoReply_MacPherson@fer3.com>
    To: luabel@ymail.com
    Sent: Saturday, February 14, 2015 1:56 PM
    Subject: [NavList] Lightning Strikes: Real Threat or Urban Legend

    The recent discussion on why celestial navigation is utilized today had me talking with some friends. Inevitably, the justification for learning CN hinged on the danger of a lightning strike frying all of the electronics while at sea in your small sailboat. This seems to be the predominate reasoning included in the back page of many education books on celestial navigation.
    I am fairly competent at taking a sight and reducing it, but my knowledge of seagoing electonics is marginal at best. I can "push" the buttions and reset a fuse-that is about it.
    I was wondering if any experts in this area could answer the folliowing questions:
    1. If you did have a lightening strike at sea, what would be the probability of losing all of your hardwired "modern" electronic navigation equipment?
    2. Would it fry your battery powered digital watches? and GPS's?
    3. Would it effect your mechanical chronometers?
    4. Someone told me that if you placed a battery powered GPS in your onboard oven, it would be protected from a lightning strike by the oven acting as a "faraday cage".  Any truth to this. I would be afraid of someone "cooking" my GPS the old fashioned way in this scenario :)
    Thanks and happy Valentines Day to all.

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