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Go Back   SailNet Community > General Interest Forums > Gear & Maintenance
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  #1  
Old 07-04-2008
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lightning

what do you do to be safe at sea in a lightning storm? how do you set up your boat to be able to handle lightning safely?
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The only 100% guaranteed solution, is planning and not being there ! We don't have that storms here frequently, but I don't take any special measure against it, except for a good and sound boat and systems. There are extensive literature on the net, including some gear used for militar antennas, etc ... Avoiding storms comes with time and experience, but I always count on the little probability of being struck, and pray for Thor to look at those masts far higher than mine ....

So (note: for me only !!), your question sounds more like "what measure you take when you fall off your boat, in a shark crowded sea ?" ....... as chances are the same here ....
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Last edited by negrini; 07-04-2008 at 04:32 PM.
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Old 07-04-2008
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I suppose if you're in the thick of lightning syotrm, there's not much you can do about it except to seek shelter where possible. I from lightning capital of the world and we don't take special precaution while at sea. Some people say lightning strikes the tallest structure around. That is not true. It strike whereever and whenever it wants (i.e. if there's a build up of ionisation charges) even when there is no storm. Where I work, lightning often strike a storage tank, but when the surrounding site construction activities changes the terrain, the storage tank seems to see less strike. The "attracter" now is somewhereelse. Btw storage tank wasn't the tallest structure.
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Old 07-04-2008
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I was just in a thunderstorm on Wednesday night with some very impressive lightning bolts and it never ceases to amaze me that more sailboats don't get hit.
My personal theory is that if the mast etc is not grounded to the keel/lake/ocean then you are slightly less likely to get hit. On the other hand if you do get hit you are MUCH better off to have everything well grounded which tends to minimize damage.
Your electronics will be fried but you will still be afloat hopefully.

Good Luck
Gary
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Old 07-04-2008
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i was struck in the bahamas just after i dropped anchor and that was after going through at least 2 or 3 storms on the way across the bahamas bank - it was a side stick and the thinking was it ran down the jib stay and out the anchor chain but it did take out all my electronics and most things electrical - about a month ago i was on the icw and sat through 5 hours of thunderstorms holding my breath - it is what it is - if i could have moved out of their way i would have - in the past i have been able to avoid some using radar and trying to move around them or slowing down or doing whatever i could to stay out of the way - but that is not always possible -
i do have a thing at the top of my mast that suppose to help - you will get all sorts of opinion on it but if i feel better about it then it is worth it being there
lightening is ligthening and it will do what it wants and only God knows exactly where it is going to go - so try to avoid if you can otherwise it is part of sailing
just my thoughts
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Old 07-05-2008
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Just remember there are two schools of thought on lightning and sailboats:

School 1—Don't ground the boat. Grounded boats are hit more often than ungrounded boats. Grounding the boat increases your chances of being hit.

School 2—Ground the boat. Grounded boats get hit more often, but suffer far less damage when they are hit. So you may risk getting hit a bit more, but you will survive a hit better.

Personally, I like the idea of not getting hit in the first place. I don't have any metal throughhulls on my boat and sinking is a very, very remote possibility in the case of a strike holing the hull. Also, I've never seen a good grounding system that made sense on a folding trimaran.
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Old 07-05-2008
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Funny how this topic has come up within a couple of days on a couple of other boards I frequent. Here is my favorite article:
Lighning and The Small Boat
It leans toward not grounding small boats, but makes the point that a lot of boats are grounded, just not well. It links to all kinds of info.

For me, the one data point that can't be explained away has nothing to do with boats. It's the tractor issue. During a storm, all kinds of vehicles are out - the vast majority being cars and trucks. So why are farm tractors with gear in the ground struck far more often than vehicles insulated from the ground completely by rubber tires? If you think grounding is a good idea, please answer that question.
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Old 07-16-2008
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Hello - new guy here and Id like to join this discussion if you don't mind.

I'm curious about where the reference information that grounding or not grounding the mast changes your chances of getting struck by lightning? I've seen two sources (besides internet bb chats) - Dr. Ewen Thomsons web site which I believe says there isn't any differences in the chances and the referenced Arlyn Stewart article which has some "data" at the very end which says there is a difference. Are there any other sources?

Regarding the tractor reference, I think its a very large conceptual leap to make a conclusion about what happens on a sailboat over water by what happens to a tractor. There are some similarities but many difference. For example, water has a very large influence on electric fields (water has a dielectric constant 80 times larger than air) and also generally has some conductivity - i.e., mobile charges. Both the dielectric constant and the conductivity of a material in the vicinity of a downcomming lightning strike are going to have some influence on the path the lightning takes. Its possible that since cars generally travel on paved roads which shed water, that it is the dry "low dielectric" soil under the cars as opposed to the wet soil under the tractor which has the largest influence on the statistics. The point is that there are lots of variables which could influence the tractor being struck which have little to do with a sailboat having something conductive in the water which is attached to the mast. Interesting but in my opinion, not at all conclusive.

I am under the impression that the water surface is very important in what happens with lightning and the premise is basically that water is much more difficult to ionize than air so much of the dissipation of the lightning charge and also the chances of generating an upwards streamer are due to effects at the water surface. This web site will explain:
(note - I cant post a link so you will have to cut and paste)

analogengineering.com/lightning/surface.html

Last edited by waltsn; 07-16-2008 at 07:51 PM.
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Old 07-16-2008
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Those photos would explain the reason nearby lightning strikes seem to be able to do far more damage than a strike on land at the same distance would. Thanks for the link waltsn.
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You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

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Old 07-16-2008
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Well...

In airplanes, we try NOT to get hit, and are supposed to give thunderstorms a 10 mile pass. Fact is airplane do get struck and they way we handle it is by effective grounding and bonding within surfaces.

Airplanes want the lightning to exit the airframe in a controlled manner through static discharge wicks, so our school of thought is control the exit of lightning..
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