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Old 10-07-2002
Sue & Larry Sue & Larry is offline
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Lightning Protection

I am considering putting a lightning protection system in my boat. The keel is lead encapsulated in the hull as opposed to a bolted-on keel. What's my best approach for a ground plate? If I bolt a copper strip or bronze plate next to the keel how should I seal the bolt holes?

Sue & Larry respond:
To install a lightning ground on a boat with an encapsulated keel your best option is to affix an external ground. You have an option of using a commercially produced bronze ground plate, like a Newmar Ground Shoe, or fabricating your own by attaching a strip of copper externally to the hull. Both of these recognized and commonly used grounds are attached externally to the hull with machine screws, washers, and locknuts. To seal around the bolt holes, use a quality marine sealant such as 101 by 3-M or Sikaflex 291. 

As lightning likes to travel in a direct path, youíll want to locate your new ground plate as close to the bottom of your mast as is practical. To ensure that you have access to the back of the plate for attaching your fasteners and ground wires, drill your first hole in the hull from the inside out. Make this first hole a small pilot hole, and then drill your full size holes from the outside in. As each hole is drilled, temporarily insert each machine screw to hold the ground in place and ensure the perfect alignment of the holes in your plate with the holes in your boat. 

Our lightning ground on Serengeti, our 46-footer, is a six inch x 18 inch Newmar Ground Shoe. Itís mounted about a foot and a half on the port side of the mast and is held to the outside of the hull by four bronze machine screws.

You might also want to have a look at the series of articles that Kevin Hughes has written for SailNet. He's a master electrician with a lot of experience in grounding and bonding systems on sailboats. Have a look at his most recent article on the topic of lightning protection: Understanding Lightning, Part Two.