How to connect the mast to the lightning ground plate is the question. As I understand it, a lightning induced pulse of electricity (average 1,000,000,000 joules or watts/sec) isn't all that keen to go around bends in conductors. However, I'm inclined to think that it's rather tricky to connect the bottom of a mast to a grounding plate without putting bends in the conductor.

Some insurance reports suggest that, having travelled down the mast, lightning has a tendency to make for the waterline of the boat, peppering the hull with small holes as it leaves (fibreglass hulls).

In an earlier thread, there was a video of a wooden telegraph pole being struck by lightning and being blown to smithereens.

Like many of you, I dare say, I've read quite a bit on lightning and protecting a boat from it. There is a mass of contradictory information out there and a few companies marketing products of questionable effectiveness, based on claims made from questionable science.

My feeling is that lightning will basically do whatever it wants, irrespective of what measures have been taken, but I could be wrong...

Anonymous wrote:The current on the surface (skin effect) is an AC phenomenon.  DC does not behave that way at all.  Lightening of course is DC.

Keel bolts are not available on all boats.

How many junk rigs have sustained lightening strikes?     As a percentage of sailboats in total they are a very small percentage.   BoatUS states that the percentage of sailboats struck by lightening is about 3 per 1000.   I assume that is annual.   Power boats 5 per 10,000.   The difference is obviously the mast height.  Junk rigged boats usually have a lower aspect ratio and shorter mast, so I would expect the percentages to be somewhere between.   An unstayed wooden mast would seem to be a less likely "target" than an unstayed or stayed aluminum mast.

A free standing fiberglass / epoxy mast would be an insulator.... but such a thing does not to my knowledge exist.

       I've heard that painting lambs blood on the "door post" of the companionway solves the problem.....but only if you are Jewish ;-)   Something I learned in sunday school as a child....

Bonjour

The "lambs blood " method, as efficient it may be, may induce some issues with the Vegans.; probably more than any lightning stike on the boat !

I would suggest an alternative that has proved to be efficient from several centuries that consist in burying  a golden coin under the mast while stepping it. Otherwise the seamen would have stop that practice !

I've written stupid things. The lightning is both high tension AND high current. It is neither AC or DC but an intense inpuls.

For a more scientific aproach to lightning there is a nice PFD presentation on the subject (aircraft oriented I'm afraid !) :

search on the web for : sikorsky lightning protection  rob majkner

https://skybrary.aero/sites/default/files/bookshelf/3553.pdf

Eric

Bonjour

As the electric curant remains at the surface of the conductor it would be easier and more efficient to use a flat conductor. It could be plain or a more flexible braid (you should not have any loop).

A way to ground the lightning on « pointies »  is to use the mooring chain in loops dropping in the sea from around the shrouds. It could be around an aluminium mast.

French and perhaps European regulation requires to link the bottom of the mast to a keel nut with a flat copper braid.

In lightning the voltage is very important but the intensity is rather small. So the surface of the grounding is not that important. On an aircraft the groundings are the little sort of brush that you may see at the wing trailing edge. But if the lightning doesn’t find a proper way it will dig a hole to the sea (through the hull for example).

Eric

I've heard of bermudan rig boats putting jump leads from their shrouds into the sea to divert the electricity from passing through the boat.

Don't know how that might be effected with a free standing rig.

Maybe from below the lower batten to over the side?

Maybe 3-4 lines from the lower mast to create a faraday cage effect?

I plan to use a copper plate, about 1 square foot. Copper surface is an antifouling by itself. Copper plate dump in the water requires copper wire to be connecter to, not aluminum one, I think. Kind of expesive set.