Lighting strikes to mast ?

[Glenn Basore]

The other day we had some pretty good thunder showers here in the north Los Angeles area which brought lighting and hail.

As a trailer sailor, I never thought to much about lighting striking a sail boat but with those tall mast it must happen right?

Glenn B

[Bob23]

Yes. A few years ago a good friend of mine had his restored Morgan 30 struck. Went down the mast and drilled 2 perfectlly round 3/8" holes in the hull below the waterline, exactly opposite each other. She went down in 6 feet of water fortunately and was afloat by the next morning.
He was quite near many other sailboats, most with much taller rigs. Why him? We'll never know.
Casualties? Electronics, the mainsail, standing rigging and almost a whole sailing season.
   Hope it never happens to anyone else.
Bob23

[skip1930]

Our friends Dave and Carol Biddick who's 30 something foot sailboat had it's mast struck by lighting while stored on the hard in Kewaunee, Wisconsin ended up with 'millions of tiny fisher-like cracks' in the hull and a massive blown out chunk where the bolt of juice found a good ground, making it impossible to float.

Dave ended up giving the boat to a fellow who chopped-sawed it up and salvaged all the parts for a boat resale shop near Racine, Wisconsin.

Lightening killed the boat.

Now in his trailer sailor book, Burgess said something about keeping battery jumper cables used for a car on board his CP-19 down in the keys and those could be hung over the side, I assume grounding in the water.

I thought about 'O' size copper cable bolted onto the back stay tang and following the transom and the trailing edge of the keel down to a welded on lug at my 6mm aluminum 'Keel Boot' that is glued on to the underside of the flat foiled keel. But then again, one must always be prepared to just walk away from the damaged boat and never look back.  After all it's only lightening.

skip.

[Joseph]

Good question. The answer is yes, it happens and sometimes with devastating results. Unfortunately, lightning is extremely unpredictable and no universal consensus exists on what's best to do... The bulk of professionals providing boat grounding advice and equipment - at the risk of potential conflict of interest - insist on the need for proper grounding(*). This usually consists in providing a straight path (no kinks!) for the lightning charge from the tip of the mast to one or more metal structures or plates outside the hull. Others will argue that this "encourages" strikes and that what is required is the opposite: no electrical connection between the rigging and the water. Some will insist on the need for a lightning dissipator (kind of a lightning rod with many points) but will differ on whether it should be electrically grounded to the water or not. In the end what to do seems to depend more on beliefs than data. So, after spending long hours consulting experts and books on these topics and having seen more electric storms above my head than I could have cared for, I've decided that lightning is one of those forces of nature completely beyond human prevention and control, and that the best preserver against their devastating power is to carry onboard a copy of the sacred book of your theological persuasion... Since none of my boats has ever received a lightning strike I must conclude that it works...

BTW, if you are ever in a boat and you realize that it has just been hit by lightning... rejoice! you've made it through... and don't move! you have just proven that spot safe, and lightning does strike more than once in the same place...

J.

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(*) There are two types of "grounding" both for very different purposes: a) one for directing electrical charges like lightning, usually connecting a lightning rod to one or more copper plates outside the hull, and b) another to provide a "counterpoise" for HF vertical antennas, connecting the "negative" terminal of the HF radio to copper strips fiber-glassed inside the hull below the water line capacitively coupling with the water outside. These two kinds of "grounding" are very different from each other and should be designed separate.