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Old 11-06-2008, 12:29   #1
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Lightning

I am strongly considering buying my first boat, and so have many naive questions. One of the first just occurred to me: Do sailers worry about lightning striking masts? I am now watching a violent thunderstorm, typical of those that roll across Florida most afternoons in summer, and am happy not to be sitting under a 50 ft mast. Is this not a concern? Thanks!
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Old 11-06-2008, 12:38   #2
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Do sailers worry about lightening striking masts?
You bet! I was worried about it last Saturday night from about 2300 to 0230. I was lucky again. <knock, knock>

Lightning is unpredictable and can fry your electronics, blow out a through hull and swamp/sink your boat - or do nothing.

But a person on a boat under a mast is considered to be quite safe - as long as you're not in contact with any grounded metal.

Dave
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Old 11-06-2008, 12:41   #3
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You're probably pretty safe, as long as the rig is well-grounded to the water.

Lightning has been a popular topic here on Cruisers Forum. Here are a few links to some reading material on the topic:
Lightning Safety
lightning strikes/ avoiding them?
http://www.cruisersforum.com/forums/...ran-11542.html
Lightning protection of boats and marine facilities
http://www.kp44.org/LightningProtection.php
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Old 11-06-2008, 12:53   #4
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Thanks for the quick replies, and thanks particularly for the links, Hud3. My sailing instructor said don't worry about it, but its hard not worry. The boat I am considering does not have lightning protection of any kind, but you've given me some reading to do.
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Old 12-06-2008, 11:04   #5
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lightening strikes

Our boat had lightening damage last Wednesday, June 4, while at the marina. Apparently terrible storm. Apparently didn`t receive a direct hit, but a boat about 8-10 slips away apparently was the one that did (a large powerboat) and we probably got a surge or something--boat was taken back to the marina where we just purchased it and they are in the process of surveying everything. Unfortunately, we had only sailed her once.
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Old 12-06-2008, 12:49   #6
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Our boat had lightening damage last Wednesday, June 4, while at the marina. Apparently terrible storm. Apparently didn`t receive a direct hit, but a boat about 8-10 slips away apparently was the one that did (a large powerboat) and we probably got a surge or something--boat was taken back to the marina where we just purchased it and they are in the process of surveying everything. Unfortunately, we had only sailed her once.
That is terrible luck! I guess lightning protection is a good idea.
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Old 12-06-2008, 12:53   #7
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That is terrible luck! I guess lightning protection is a good idea.
There is no lightning protection.
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Old 12-06-2008, 12:58   #8
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There is no lightning protection.
Any thoughts about the bonding and grounding systems described in Ewan Thomson's booklet (http://www.kp44.org/ftp/LightningAnd...daSeaGrant.pdf)

Is that a waste of time and money?
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Old 12-06-2008, 13:02   #9
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bonding, no bonding whatever, there is no evidence that it makes any difference.
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Old 12-06-2008, 14:30   #10
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There is no way to prevent lightning from striking a boat. There are techniques that can be used to increase the chance that you will not be injured and the boat will not be sunk by a lightning strike. However, even using these techniques, the boat's electronics and electrical equipment will still be at risk of damage.

Fiberglass and wood sailboats are a real "hard case" when it comes to lightning protection/mitigation. The best that can be done is to tie everything metal together and provide as much grounding as is practicable.

The major risk during a lightning strike is when the lightning seek a path to the sea that goes through you or the hull of your boat. This is known as a "flashover" event. Lightning will take ALL possible paths to get from ANY metal object above the waterline to the sea. To prevent flashover events all metal objects aboard should be connected to a common seawater ground. This includes stays, shrouds, air terminal, mast, poles, sail tracks, lifelines, stanchions, anchor(s), anchor chain(s), tanks, through-hulls, electrical components, electronic equipment, RF grounding plates, engines, etc. As an example, the recommended wire size for the connection from the masthead located air terminal should be #4 GA tinned copper. However, an old stainless steel backstay would work as good or better. For the other connections #8 GA tinned copper or equivalent should be adequate.

The purpose of the #4 Ga wire is to ensure that as direct and uninterrupted path as possible exists between the masthead and seawater ground. This is much better then letting the mast rise to tens of thousands of volts relative to other metal object in the cabin or to the surrounding seawater. This rise in potential would most likely result in a flashover event that could injure someone or blow a hole in the hull. The goal is to ensure that flashover events don't occur by keeping all metal objects at the same electrical potential. And to do this it is necessary to bond every metal object together.

Some common sense is required when making these connections. If an anchor is laying on a already grounded anchor roller then it too is grounded. However, the bitter end of the anchor chain connected to that anchor should also be taken to its own ground. That way a flashover event is less likely to occur between the pile of chain and seawater that includes someone in the v-berth and hull of the boat.

And, yes, if time and circumstance permits, isolating electronics by disconnecting the antenna and power connections can't hurt the electronics. But, it may be safer to not be holding on to a random piece of wire when that big bright bolt from the sky hits.

BTW, if you use low inductance connections to connect the above items together you will by default have a very good RF ground system. Low inductance connections can be made using copper or stainless steal tape and braid. The stainless will last longer.

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Old 12-06-2008, 15:44   #11
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We also had a boat a couple slips away hit a few weeks ago. That boat loss all electronics. A/c motors, batteries, radios, you name it. The guy was watching TV and WOW it blew up right in front of him. We loss the boat's stereo, a/c salt water motor, and the battery charger. Nature can be unfair at times.
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Old 23-06-2008, 10:26   #12
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Devastating lightning strike to cat in the Bahamas

Eric Kraft sent me these photos of the aftermath of a lightning strike on June 20 to a 46' charter catamaran at Marsh Harbour, Abacos. He comments "Miraculously, the clean-up crew aboard were not hurt and escaped the conflagration safe but extremely shook up. By the time I found out about it, the volunteer fire brigade was just pouring water onto the smoking wreck. It was obviously a total loss."

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Old 23-06-2008, 11:15   #13
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This is a very timely thread. This weekend, while up the mast, doing some rigging, I was watching a squall form out in the bay. The first one past us to the north, so I was not too concerned, but the second one started in, and about the time I was 3/4 way up the mast, I was seeing lightning strikes within a mile of me. By the time I got to the deck, there was a strike about 200 yards away on a building. We are relatively safe, considering there are other masts near by, and we are up on wood blocks, but somehow being 50' in the air on a metal mast with lightning that close just made me a little nervous.
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Old 23-06-2008, 12:37   #14
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