NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Lightning at sea
From: Trevor Kenchington
Date: 2004 Oct 15, 21:39 +0000
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@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