lightning strikes/ avoiding them?

[GordMay]

I don’t really have any personal anecdotal evidence that the Dynaplate isn’t an effective lightning ground electrode, but most (*if not all) the authorities agree:

1. The increased surface area, due to the “bubbled” surface, does not increase the plate’s effective area. The bubbles are so close together, that the surface area is only equal to the outside dimensional area, once the lightning gets a minute distance into the water. Accordingly the plate is too small (minimum of 144 square inches in salt water, ‘more’ in fresh).

2. As noted, the theory suggests that the water enclosed in the cavities between bubbles can vapourize explosively.

3. The most recommended lightning ground electrode is a long strip, perhaps 4" wide x 1/4" minimum thick, and 36" minimum long, installed on the outside of the hull, from the base of the mast, leading aft. The ends should be secured with two fasteners, to prevent “twisting” under dynamic loading. Strips are recommended due to their increased “edge length”, which form better attachments than flat surfaces. Do not fair the edges, but allow them to remain in “sharp” contact with the water.

4. Ewen M. Thomson has patented a new electrode geometry, claimed to be more effective.
Goto: http://www.marinelightning.com/ and see the patent at:
http://www.marinelightning.com/USPTO...708638_001.pdf

[CaptainK]

Ewen Thomson of the University of Florida, happens to be the foremost expert on the topic of lightning protection.

The very long post. That I posted on Feburary 6th. Alot of that was based by Ewen Thomson's research. I have copied, and made word document files on his research in the past. And find his articles fascinating.

But this new desgin that he has now. Sounds more workable, than his older designs. This might be the one everybody has been looking for?

[Steve Rust]

I was sailing during a thunderstrom once when I heard a ticking noise behind me. I could see tiny sparks of static electrcity jumping the backstay insulator. I did not get hit but it made me very nervous. I had read that one theory is that a buildup of a static charge may attract a strike. My boat has a center cockpit sitting over the centerboard trunk. There is a 6' long x 2" x 1/4" copper plate running down the forward edge of the trunk and fastened to the mast by a large gauge battery cable.

[CaptainK]

A static charge can attract a lightning bolt to your mast!!

So yes Steve. You are very very correct!!

Bet that made your hair stand on end
It does bring to mind a concern I have. I have a chain set up for my boat that snaps onto the shroud and drags in the water as a lightning ground. What I am wondering is can the chain generate static electricity from dragging through the water? I know metal dragging through air will, but what about salt water? I agree that static electricity will attract lightning. I have heard of way too many related instances to discount this as a myth.

[CaptainK]

I don't think so Kai.

But it very might be possible. But, I doubt it.

Your chain from the shroud. Which boat is it on?

Which ever boat I am sailing on. It is just an 8' piece of 3/8" chain with a snap shackle. It is currently in my storage shed with the rest of the pieces to the Challenger.

[CaptainK]

It should work.

But it would work even better. If you had a ligtning rod (there's another name for it..dissapator?)

Start with a dissapator (lightninig rod) at the tippy top of the mast. Then the thickest insulated copper wire you could get your hands on. Connect the wire to the lightning rod at the top.

Run the wire down the mast to that chain that you were talking about. Connect the copper wire to the chain. And when you're out sailing in parts of the world, were lightning is frequent. Just throw the chain down over the side. And you have a path, for lightning to travel.

Remember this everybody. Current runs along the least path of resistance. And that's the most direct path. You do not want that lightning bolt to travel around through your boat. And short out all your electronics.

Another thing to remember is this. Even if you this idea I stated here. I would still advise the extra caution, of dissconecting your radio antenna. And disconect all your electronics from the electrical outlets. Just incase a stragler bolt goes dancing along the wires?

Reasonable, but that is not what I was asking. While I have a good grasp on electronics, and grounding systems, static electricity is still a mystery to me.

[CaptainK]

Static electricity is a mystery to me as well, Kai?

Were both in the same boat, called mystery!!

I guess I missed my turn to play with the tesla coil when I was a kid

[CaptainK]

Played with Tesla coils alot in Jr. High!!

I used to get the girls in the classroom with the static charges, and zap them in the right spots!!

If ya know what I mean?

[Steve Rust]

I think CaptK may be confusing a lightning rod with a static dissapator. Two differant animals. The lightning rod should terminate in a sharp point and be the tallest thing on the mast. As most of us also have a vhf anntenae up there this can sometimes be a problem. I decided to accept a few miles less vhf range and mount a powerboat stlye fiberglass whip on the stern pulpit. The static dissapator looks like a dried out dandelion on a medal rod and supposedly will dissapate the static charge buld up. Should also be located at the masthead.
To throw a few thoughts out there. What you want is the most direct path with the least amount of turns and bends. On my boat it is a straight shot from the masthead to the grounding strap in the centerboard trunk. Of course this may not always be possible and the chain clamped to a stay may be the only option. I recall reading that stainless steel is a poor conductor compaired to copper or aluminuim, so would the main charge tend to follow the mast and not the stays?
It seems there is no 100% correct answer to this problem. My own boat was hit before I owned it and before the ground strap was installed. It blew six tiny pinholes at the waterline. Small fractures radiated out several inches on the inside but were not evident on the outside. It looked like a daddy long leg spider. There was some disscusion about ungrounded boats being less likely to be hit and while this may be true if you are hit the lighning will be seeking a path to ground through the hull.

[CaptainK]

Correct Steve.

A static dissapator. That word kept evading me while I was typing this last night. Sorry about that!!

[CaptainK]

Steve!!

So when the lightning struck that boat, before you owned it. Besides the (six) pin holes, with the daddy long legs cracks. The lightning never blew out any through hulls?