NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Lightning at sea
From: George Huxtable
Date: 2004 Oct 15, 22:34 +0100
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@huxtable.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. ================================================================