Lightning Arresting

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Lightning Arresting

Postby OldRover » Thu Jun 07, 2012 11:52 am

I have seen some damaged masts, both aluminum and CF, and decided that I should use an arresting system. I had a few good conversations with Eric Sponberg regarding CF masts and he suggested that a lightning arresting setup is mandatory. He referred me to some info on his site as well as a couple of other engineering sites. I have seen the topic somewhat touched upon here, but I have one question still outstanding. I like the single spike lightning rod as opposed to the brush type. Connect that to battery cable through the mast. And then 'ground' to heavy metal below the waterline. The last part is where I am having a problem. Anyone else install a lighting arresting system? Where did you terminate? I have used keel bolts on other boats. I have seen the largest seacock used, but not sure that provides enough of a path. Although I am leaning towards this since there is a large seacock in the bilge that is very close to the main. The other question is should both masts be protected? Currently I am installing in the main and think the foremast will be OK since it is shorter. Maybe I will run a cable there at a later date.
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Re: Lightning Arresting

Postby sailmon » Thu Jun 07, 2012 1:19 pm

Two thoughts - and I am by no means an expert.
Lightening is completely random and unpredictable in its behavior. You should not count on your taller mast to protect your shorter mast. I've seen boats where the lightening ignored the 57 foot aluminum mast and enter at the 12 foot wind generator post.
Second thing is that lightening never exits neatly and again is not predictable. By grounding to a seacock I suspect you risk a lightening strike blowing out the seacock... which could leave a 1 to 2 inch hole in the bottom of your boat. My guess there are better alternatives.
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Re: Lightning Arresting

Postby Michel » Fri Jun 08, 2012 10:42 am

I have / had a lightning protection on my F44. I removed part of it because we have no severe lightning here. There was a 3' aluminum spike on top of the main mast connected via heavy gauge cable to the keel. I would never use a seacock as exit point for current; suppose it melts! I also read that the cable should have round bends in order to make sure the the lightning does not shoot out in a corner. No this is no joke.

Attached is an article with info about corrosion, zincs and bonding and it discusses lightning protection as well.
Attachments
Corrosion, zincs and bonding.pdf
(316.01 KiB) Downloaded 270 times
Michel Capel, Freedom 44 #4 1981 'Alabama Queen', NED8188, cat ketch with wishbones, home port Enkhuizen, the Netherlands, 52*42.238'N 005*18.154'E.
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Re: Lightning Arresting

Postby OldRover » Mon Jun 11, 2012 8:54 am

Michel, I actually did read that article. It helps with the debate over boding. How exactly did you have your cable bolted to the keel?
I have decided that the seacock is too risky. The 1.5 inch is probably meaty enough that the cable would fail first, but I'd hate to find my mast being svaed from the strike sticking up out of the water due to a blown seacock/thru-hull. The up side is that I have cleaned out the bilge and looks like I have plenty of room to drill and set a bolt into the keel while keeping the cable run just a couple of feet beyond the mast.
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Re: Lightning Arresting

Postby daletournier » Mon Jun 11, 2012 11:15 pm

I guys, im currently around alot of lightning and are also thinking more in regards to lightning protection. What size wire (gauge) down the mast are we talking about?
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Re: Lightning Arresting

Postby OldRover » Wed Jun 13, 2012 5:52 pm

Use a minimum 4 gauge for up to a 50' mast (this was what Eric Sponberg told me). I am using 2 gauge. Bigger is better when it comes to lightening, unfortunately hanging heavier is not better when it comes to hanging stuff in the mast so you pretty much need to stick as close to minimum as possible.
You may want to check out: http://www.marinelightning.com/index.html
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Re: Lightning Arresting

Postby daletournier » Thu Jun 14, 2012 8:29 am

Hi all, just read the article oldrover suggested. Something i found interesting was that catamarans are more likely to cop a lightning strike than monos. Ive spent the last 12 months in the Malaysian/Thailand area and the two boats that i know that have had a lightning strike have both been cats, in fact one of them got hit 3 times!Also there is a big cat in the marina at the moment with a aerorig,coincendtly as i was having a look a friend of mine that i hadnt seen for quite sometime walked up, its turns out he helped repair the boat twice in Panama after it was hit twice by lightning. I asked him about lightning protection and he said the boat had it yet lightning still blew a hole out of the top of the mast where it exited prior to blowing a hole in the boom.
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