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    Re: Lightning at sea
    From: Trevor Kenchington
    Date: 2004 Oct 15, 21:39 +0000

    I have been scanning the messages on this thread with growing disbelief:
    Contributors who are so well versed in navigation techniques seem
    willing to express themselves on an issue, lightning protection, on
    which they seem woefully ignorant. It is off-topic for this list and, in
    any case, I don't have time to type out even an abbreviated account. But
    I would recommend that anyone operating a boat in lightning-prone areas
    should pay close attention to Henry Halboth's contribution:
    
    > Current criterion recommends that vessels of the type being discussed on
    > this List be fitted with adequate lightning protective devices. In
    > capsule, this generally is construed to consist of a common ground
    > conductor, connected to a suitable ground plate, and to which all items
    > to be protected are grounded. The specifics of such a system are beyond
    > the purposes of this List, however, those interested, and probably should
    > not be sailing without such protection, are referred to the ABYC
    > publication ""Standards and Recommended Practices for Small Craft" - at
    > one time lightning protection was Section E-4. Please don't assume that
    > such protection is in your vessel just because you spent a lot of money
    > for it - it may not be.
    
    George, sailing in the English Channel, may be able to get away without
    worrying over ground plates and lightning bonding. Anyone who operates a
    boat in Florida or the Chesapeake in summer cannot.
    
    
    Since someone is bound to think that I am being unduly harsh, I will
    give a few examples of errors in this thread:
    
    > But if it's going to hit your boat anywhere, it's almost certainly going to
    > be the top of the mast.
    
    
    Try mounting a VHF whip antenna on the taffrail and the relative
    probabilities of being hit on the masthead or the antenna will be not
    far different from the ratio of their heights. Alternatively, if you
    have the typical low mast of a powerboat, the bow and stern of your
    vessel will have significant probabilities of being hit.
    
    > It's worth
    > trying to deter current flow down the rigging wires
    
    Professional opinion is that it is worth trying to facilitate current
    flow down the rigging by bypassing rigging screws and the like with
    heavy-gauge copper conductor, so as to avoid the heating and sparking
    that would result if lightning had to jump the breaks in continuity.
    
    > I do my best to keep away from any metal fittings that intrude from
    > outside
    
    Better to keep away from any metal inside too, or at least be careful to
    avoid contacting two different pieces of metal. The massive current
    flows involved in a lightning strike will induce very considerable
    voltages in any nearby conductors. It is not desirable to provide a
    route to earth through your body.
    
    > 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.
    
    
    In lightning-prone areas, careful boat owners do indeed hang the end of
    a conductor over the side when they leave their boats. The problem with
    just dangling something from the foot of the mast, however, is that it
    would likely form a right-angle bend in the conducting path which won't
    do the job. There are minimum radii of curvature requirements in
    lightning conductors.
    
    
    Again: Follow Henry's recommendation and the ABYC standards if you are
    operating in areas where lightning is at all common.
    
    
    Trevor Kenchington
    
    
    
    --
    Trevor J. Kenchington PhD                         Gadus{at}iStar.ca
    Gadus Associates,                                 Office(902) 889-9250
    R.R.#1, Musquodoboit Harbour,                     Fax   (902) 889-9251
    Nova Scotia  B0J 2L0, CANADA                      Home  (902) 889-3555
    
                         Science Serving the Fisheries
                          http://home.istar.ca/~gadus
    
    
    

       
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