Home Plate

John Manzano of Charlottesville, Virginia, asks:

"I am planning to install a copper grounding plate on the hull of my Pearson 365 for lightning protection, but I’m not sure how to connect the mast and shrouds to that plate. The boat has no keelbolts. Do I drill a hole through the hull, and if so how big should the hole be? What should I use to seal the hole?"

Don Casey replies:

If the hull is thick enough that short self-tapping screws won’t penetrate to the interior you can use these to fasten three corners of the grounding plate. For the fourth corner you’ll need a bronze bolt that penetrates the plate and the hull to serve as a wire terminal inside the boat. I suggest using a 3/8in bronze carriage bolt. Before you install it, file the hole in the plate to make it square. This will keep the bolt from turning when the retaining nut inside the hull is turned. The bolt must be long enough so that you can secure it against the hull with a shoulder washer and nut, and still have enough bolt length to accept all the wiring ring terminals, along with a second washer and nut to hold them in place. Use a polyurethane sealant, such as 3M’s 5200, to seal the bolt and mounting screws.