Dear Sailors:Last summer, I was reefing the sail, had my hand on my aluminum mast, and a thunderstorm that was a mile away sent an invisible charge my way and gave me quite a shock with a boom that I think was caused by the main bolt hitting a nearby ridge. What are the odds of getting a strong bolt through the mast? What will occur? We were sailing down in the Keys last month, and a lightning bolt hit a sailboat mast while the boat was on the trailer, out of the water. The mast glowed red for five minutes. I can’t find any information on this subject. Does a lightning bolt destroy radios? Can it hurt the hull? Best regards, Chris
Hi Chris:The entire subject of lightning is not totally understood, and the odds of being hit difficult to quantify. I am by no means expert on the subject, but here is what I think is the case:
1. You want to make sure that all the metal aboard is bonded electrically, so that if you do take a direct hit, your body does not become the means of equalizing the charges between various bits on the boat–that can be a fatal experience!
2. It is better to avoid the strike in the first place by bleeding off the ion charge which precedes the bolt from the cloud. This is done with brush like devices, typically placed on the masthead, and proper grounding of the spars and rigging. On our fiberglass boats we typically fit a sintered metal bonding plate below the heel of the mast to help in this regard.
This is all covered in somewhat more detail in our Offshore Cruising Encyclopedia.
Good Luck.
Posted by Steve Dashew (November 30, 1999)
