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    Re: Lightning at sea
    From: George Huxtable
    Date: 2004 Oct 15, 22:34 +0100

    Courtney Thomas asked-
    
    >What do you think of a fiberglass boat with iron ballast and aluminum
    >mast, regarding lightning damage evasion ?
    >
    >How about bonding the aluminum mast to the iron [internal] ballast, then
    >ballast to sea ?
    >
    >But, I ask....what then, in this case, would be the best procedure
    >regarding the ballast to sea connection, as well as, mast to ballast ?
    
    ======================
    
    Courtney doesn't say whether his mast is stepped on deck or down below.
    
    With internal ballast, I suggest that for lightning protection purposes,
    bonding the mast to the internal ballast would be asking for trouble. This
    would take the ballast up to the instantaneous voltage of the mast, and
    apply that voltage across a large insulating area of fibreglass, separating
    that ballast from the sea outside. It could be the perfect way of devising
    a test system to search out any points of electrical weakness in that
    insulation layer, and then if one is found, bang! and the sea can get let
    in through the resulting hole. JUST what you don't need! I would leave the
    internal ballast unconnected, if it was mine.
    
    You could drill a hole in the hull and fit a metal plate outside it (rather
    like an anode fitting) in contact with an always-wet part of the hull, with
    a really substantial feed-through so that no lightning strike could ever
    evaporate it, bonded to the mast internally by a stout copper strap. You
    would have to be careful about electrolysis, inside and outside that
    hull-fitting. Me, I like to minimise such holes in the hull, so I would be
    reluctant to go that way.
    
    I would prefer to dangle a stout electrical lead from the mast foot into
    the water, in times of electrical storm. Of course, that's no protection
    when you leave the boat unattended.
    
    One suggestion I would make is not to use the croc. clip, usually fitted to
    such jump leads, to connect to the mast foot, as being likely to evaporate
    with really high currents. I would make a loop of the wire and fix it to
    the mast with some sort of stout nut-and-bolt, instead.
    
    But to be honest, I'm no guru on lightning protection, it doesn't fill my
    thoughts (except on certain dramatic nights), and I can offer Courtney no
    more than what strikes me as commonsense.
    
    George
    
    
    ================================================================
    contact George Huxtable by email at george---.u-net.com, by phone at
    01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
    Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    ================================================================
    
    
    

       
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