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Telstar 28
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992 Posts
The brush like lightning dissapators don't make much sense on a boat, since they require a fairly decent ground connection, which most boats lack.

There are basically two schools of thought on lightning protection on sailboats.

1) Ground the boat, and bond all the major metal structures to the lightning grounding system. This will give lightning a path to the water in the case of a strike and also act to protect the occupants as much as possible. However, grounding the boat as such will increase the chance of getting struck slightly.

2) Don't ground anything on the boat. This reduces the chances of you actually getting struck. However, if you do get struck, the chances for catastrophic damage go way up, as sideflashes may occur and there is greater risk to the occupants of said boat.
 

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Telstar 28
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992 Posts
Rick-

Statistically, from what I've read, an ungrounded, non-lightning bonded boat is less susceptible to being hit, but if it is hit, will generally suffer much greater damage-like blown out through-hulls, pinholes in the laminate where lightning passed through it, damaged chainplates from sideflashing, etc.
Brushes are wire brushes... they contain a LOT of "points" to dissipate static and are by virtue of the amount of AREA better than a single point.

School of thought #1 above is correct....

School of thought #2 above is incorrect....

Salt water is VERY conductive. Fresh water is almost NON-Conductive, but will still kill you if you're in it and lightning hits near by (near by meaning within up to 10 MILES).

It amazes me to see some of the stuff that people put on the internet in this forums that they "believe is true" because "they have seen it".

I've read a dozen or so things about radios and antennas in this forum and on Cruisers forums that are just plain wrong, and sometimes dumb.
Not disagreeing at all with your description of lightning or how dangerous it is....

Lightning, if there is a DIRECT STRIKE can and will KILL you, and destroy every piece of electronic gear on your boat. Period. REGARDLESS of any and ALL protective measures you take.

Lightning is a non-discriminatory function of electrical energy and will seek the path of least resistance to ground (or in the case of the boat to water). It can and probably WILL be through your electrical system. It most LIKELY WILL destroy everything connected to the battery/electrical systems.

At the extreme amperage ratings of a bolt of lightning, and the unpredictability of what it can (and WILL) do you have to assume the worst is possible, take every precaution and then if the boat is hit, hope it paths to the water over the surface of the wet deck, and not through you, your electrical system and other people.

But, NOT taking ANY precautions at all will ensure that whatever is highest (your mast) will conduct the next bolt through your mast, to the hull, where it will leap to the electrical system (lighting on the mast) into your electrical system.

Placing a lightning rod on the highest points of the boat and surge arrestors on equipment will reduce the damage, but not completely mitigate it.

It takes approximate 600 volts to jump across one mil (1/1000th of an inch)... A lightning bolt typically A lightning strike can be from 300kv to 600kv, and can push as much as 15000 - 20000 AMPERES (current, the stuff that will kill you). It takes 10 milliamperes to stop your heart.

Remember the 600 volts and 1/1000th of an inch? Lightning can travel many MILES...

Don't play around in it, and don't play with it. Put protection up on the boat, and stay under cover if you can in a storm. (Obviously you might not be able to do this caught IN one at sea, but don't make yourself a target either).
 
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