Electric grounding to the Keel

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6 years 11 months ago #2532 by Jim Allaway
We sail Next Horizon, W42 #312, based in Milwaukee, WI. I am interested in hearing how other W42 owners have directed their electrical ground to the keel for a lightning ground. I have not seen any references on this site or others of such a ground to keel on a W42 but I am confident this question has been thought about by W42 owners. The encapsulated lead presents a construction problem, but hopefully not significant. On Next Horizon, the built-in Port water tank has been removed and replaced with two smaller tanks which occupy less space than the original tank. As a result, there is convenient access to the bilge area directly above the keel. I have considered accessing the lead in the keel by drilling down at this site through the glass layup and through the bedding mineral material (cement?). A substantial conductive cable could then be sent to the lead, and sealed in place. The main mast step is a straight line away from this grounded cable. A substantial grounding plate would then be attached to the exterior of the keel with conductive bolts sent directly into the lead of the keel. Certainly, the presence of even small amounts of water from these modifications, behind the glass layup, would present a mighty hazardous vaporization potential during a lightning event, and would be rigorously avoided.
The bonding system on Next Horizon is extensive and we are well-grounded through the engine and one Dynaplate. Also, we trail four substantial copper cables from shrouds, including the split main backstays when electrical activity is present in the area. We have been lucky, watched many strikes into the sea near us and we are still waiting for our first onboard lightning strike. Still, I would rest more easily with a good, direct-as-possible electrical route to water.
Thanks for your thoughts!
Jim Allaway
"Next Horizon"
W42 #312, FtMeyers, 1981

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6 years 11 months ago #2533 by Michael Smolek
Jim- I am certainly no expert on lightning grounding in boats, (if there is such a thing, since there is so much radically differing views on the subject). One thing to consider is that your lead MAY not be a single piece of lead. I don't know how the Ft Meyers Whitbys were built, but my Brewer 12.8 (the 7th one built in Ft Meyers ) has at least a portion of its lead in very tiny lead bbs. These were poured into the previously laid-up keel cavity in a fiberglass resin slurry. So the keel might not provide a single, straight line conductive path large enough to handle a strike. My boat has four grounding plates all on the hull above the keel and these appear to be connected to the bonding system and rigging, although I haven't mapped all the connections, so I can't tell you precisely. The wire connections to the plates are inside the hull, to bronze studs and through bolts. BTW this is my fourth boat in 40 years of sailing in some lightning prone areas (Fla, Bahamas, Chesapeake) --two boats with some kind of lightning grounding and two with ungrounded rigging. All I know is that I have never been struck, but I also always worry in the height of the storm if a grounded or ungrounded system is the right way to go. And if it is grounded, is the system adequate or is it just enough to attract lightning.......Mike Smolek Brewer 12.8 Hawk

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6 years 11 months ago #2534 by Robert Strickland
On Allegria, we have been struck once which resulted in all our 12 volt equipment being fried. As previously mentioned, there is a lot of differing opinion regarding lightning protection. The only thing I know for sure is that there is no absolute protection from a strike. There are, however, things you can do to minimize the chances of a strike and protect the occupants of your vessel. I'd suggest reading the webpage of Dr. Edwin Thompson of the U of Florida ( google lightning protection) for an intelligent discussion of options.
On Allegria, what we have done is put an air terminal at the top of the mainmast and bonded the mast and upper shrouds with large cable to 3"x48"x3/8" bronze bars mounted external to the hull with a 3/4 " spacers and mounted with 3 bronze bolts. The bars are 6-8" below the water line, one on each side.
We also keep our fingers crossed and karma full when thunderstorms come.
Dee, Allegria #199

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