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lightning grounds
Jere Lull wrote in message ...
In article , (Parallax) wrote: We often see some discussions about lightning protection but here in FL, it is really a major problem snip My normal lightning protection method is to try to get it to ground as quickly as possible. I have a 2'X2' copper sheet with a very large tinned copper braid soldered and crimped to it that I drop overboard. The otehr end of the braid has two welding clips that I attach to the upper and lower shrouds near the deck. I turn off and unplug all electronics and stay away from all metal fittings. I have even considered a retractable Faraday cage attached to the mast head consisting of small wires to protect the boat inside it. Am I too paranoid? Having lived in Clearwater for 5 years, I'd say "NO!" to being paranoid. Sometimes they ARE out to get you. My 28' S2 has internal ballast, otherwise I'd use the keel as ground. Being VERY familiar with high voltage discharges, I use braid because such discharges have high frequency components so they need a lot of surface area to carry the current. I considered fastening the copper directly to the hull with the braid fastened from inside but considered: 10,000 amps X10,000,000 volts = 10E10 watts dissipatted in about 50 nanoseconds,sorta like hitting your hull with a big sledgehammer. Thunderstorms in Clearwater may be even worse. In that area of FL, I'd probably have leads hanging from all 4 "corners", permanently attached with bulldog clamps, not dinky welding clips ;-) They would be clipped to something while under way. I figure about 6' of copper strand in the water is sufficient and plates are bulky, so would use zinc guppies to weigh them down so they could "live" in the water while we were away from the boat. However, I am curious about lightning protection for less afflicted ppl. I have seen these ground plates consisting of sintered bronze powder that are fairly small but have high surface area due to the many sintered particles (Dyna-Plate). I can believe these may work for low E fields and low current but I do not believe they work for high fields and high currents (like lightning). I think the small passages act like tiny Faraday cups allowing no field inside and the effective surface area is not much larger than the external area. What do others think? That sounds sorta reasonable to me. Our iron keel is our ground, so I haven't worried about it much. I believe most people hope that making the mast "look" like ground with a good Dyna-Plate or similar will protect them. Personally, I think that making a Faraday cage out of the shrouds is the best bet, but there are no guarantees. Friends put one of those bottle brushes up on the mast -- factory approved tech did it -- and they got struck a week or so later. |
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