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Old 12-12-2007, 18:54   #1
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Lightning protection for a catamaran

I am looking into fitting some sort of lightning protection to my catamaran (FP Athena) and I am wondering what others have done to their multi hulls ?
I was thinking of making a heavy earth strap that I can attach to the foot of the mast when required, that is lowered directly into the water, but theory has it I should also do the same for both shrouds and the main stay, maybe even the boom as well to prevent serious arching and hull damage.
Any thoughts ?
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Old 12-12-2007, 19:02   #2
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I'm building in a length of 32mm conduit through from the deck to under the bridgedeck next to the mast. I will have a length of solid copper rod I can lower through the conduit into the water, and bolt onto the mast.
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Old 12-12-2007, 23:04   #3
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Check out the website of what may the world's leading authority on the subject, Dr. Ewen Thomson. Marine Lightning Protection Inc.

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Old 12-12-2007, 23:47   #4
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Intentional Drifter,

Thanks for the post. I have read all the theory (including the site you mention), but I am more interested in what other cruisers have done and the method they have used such as the post from 44'cruisingcat. It's all good in theory, but often very difficult in practical terms.
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Old 14-12-2007, 08:00   #5
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Flashover

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Originally Posted by Crak View Post
I am more interested in what other cruisers have done and the method they have used such as the post from 44'cruisingcat. It's all good in theory, but often very difficult in practical terms.
Having taken a hit to my mast and losing everything electric connected to 12VDC, I'd be very interested in responses to your question. From the reading I've done, short of turning the boat into a mass of heavy gauge wiring there isn't much that can be done.

The problem that I've experienced is "flashover". The extremely high voltages involved just jump the gap in conventional surge protectors, or circuit breakers.

The ultimate answer? Stay out of shallow waters.
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Old 14-12-2007, 13:28   #6
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I second 44 cruising cats suggestion, there is a device called strikeshield that might do the same thing.
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Old 14-12-2007, 15:02   #7
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The jury is still out on the actual science of the lightning strike--but I made my living fitting lightning protection to electrical outside plant and I can tell you what works and what is a waste of time. Forget about "experiments" where high voltage generators discharge into buckets of water etc. They bear little if any resemblance to a lightning strike, a moderate one which has the power dissipation of the order of 10 to the power of 12 watts.

There is no practical size of lightning conductor able to conduct this magnitude of discharge to earth during the short few milliseconds of a lightning discharge without being vaporised--so all conductors, even those which do conduct significant portions of an initial and subsequent discharge to earth, have "bled" most of the charge before the air became sufficiently ionised to allow the balance of the discharge and any subsequent or consequent discharges to reach earth through the conductor itself. If you think of the steel-melting capability of a reasonably powerful arc welder as being about ten thousand watts, you get the picture as to the metal-melting capability of the spark from a moderate lightning discharge.

It is possible for a yacht to be at sea with no discharge protection and not be struck, and the reason forn this is simply that they were not the point on the "capacitor plates" where the "dielectric" was weakest. Because the strength of this dielecttric is not a constant, and niether is the conductivity of the earth (the sea is pretty consistant though), variable factors something most of the experiments do not take into account, sailing without lightning protection or feel-good protection based on wishful thinking or tiny-tots sufrface-skimming experiments is like buying lottery tickets where the prize is severe burns, death, and damage which might extend to loss of the vessel and crew.

Now--because the turbulent air does not have constant electrical properties, there are rising and falling columns of air, air at different moisture contents and temperatures, and the potential lightning-forming charges in the air are not evenly distributed and are rising and falling in strength all of the time, tiny-tots experiments are a complete wank.

Some of the best labopratories have studied this phenomena, testing only one facet of the discharge sequence at a time because that is all that can be tested unless one goes outside and studies the real thing from satellite photographs etc, and actual discharge sequences. Sometimes these are artificially initiated.

None of the outside plant to which I had fitted simple dissipative protection was ever seriously damaged by lightning after the protection was fitted, although unprotected plant was an expensive damage bill waiting for presentation.

People think of the earth and the charged clouds and moisture and dust particles in the atmosphere as though they were separate conductors, whereas it might be better to think of them as plates of a leaky and badly out of balance mega-capacitor, with the turbulent and irregularly insulative/conductive lower atmosphere as its dielectric. Make sense so far?

OK--some simple facts.

You do not have to use copper--going up a guage or two in aluminium works just as well and will not cause corrosion if you wish to keep your electrode in the water while you are absent from the vessel. The last one I used was a plate of marine aluminium alloy, about 6 mm I think, and it swung up and down on a pantograph between the hulls. It dropped into the water and could be used while sailing because the wires which suspended it also acted as lateral braces. It protruded below the hulls by about 300mm--but it would have made little difference if it had not. It could be hauled up out of the water by a lanyard and secured. To this was fitted an aluminium strap which I got from a power distribution company--which led to the base of the mast. The mast itself then became part of the dissipation path--and at the top of the mast was a single rod sharpened to a point. Before this I had used the brush collectors--but the rod was simpler and had less windage.

Now--when there is the potential for a strike several factors have to be present. The air has to be ionised for the initial strike to occur--the air has to be moist to be able to become ionised easily, and the air has to be highly charged in order to create the electron flow and potential differences throughout the air mass between earth and sky for subsequential and consequential discharges.

Enter the earthed rod.

This plus the boat and her rigging act as a huge discharge sink for electrons, which stream from the surrounding charged air on to rigging and lightning rod. Sometiomes the discharge is so intense tht it becomes visible as streamers of white or blue, or sometimes blue flickers, the St Elmo's fire old salts used to sea on the wet rigging of sailing ships on the wool and tea routes through tropic seas and cold Altantic storm waters alike.

If you can bleed enough charge from the air surrounding the top of your vessel, you greatly decrease the likelihood of an initial strike. Even if you are struck--very unlikely, so much of the discharge will already have taken place that your damage may be significantly lessened, but I am only theorising here because I have never seen a strike of any kind on properly protected plant.

OK--the initial strike will ALWAYS occur where the dielectric strength of the atmosphere is at its weakness, but once there has been a change to the balance caused by the initial strike, the whole system changes and many other charged particles and areas of high charge density elsewhere in the atmosphere will opportunistically discharge into the same discharge path--greatly multiplying the effect of the initial strike.

Best you do not encourage that initial strike--because if that is what you think your lightning conductor is for--lotsa luck!!

A building is set up with several conductors, usually at least four, one going down each wall. The boat can be rigged the same way using the shrouds, and I have always done this. They do not have to be connected at the base--they collect and discharge via the top of the mast just fine.
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Old 14-12-2007, 19:44   #8
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Mike,
Thanks for the detailed post. It's clear the subject still excites you and we have all benefited from your knowledge.
I carry a hand held backup gps and VHF radio for such situations, as I work on the assumption all electronics will not survive a direct hit. These are kept in the oven during a thunder storm, as its the closest thing I have to a faraday cadge. My intention is to do as you suggest, connect a heavy gauge aluminium cable to the mast foot and dangle it vertically into the water. Even if this should vaporize, its better than me or one of my family vaporizing and it should help prevent any side arc's blowing a hole in my hull. Although far from perfect, short of wrapping the boat in bonding straps and lighting rods, I feel this method will offer the best protection for $ and effort and will offer far greater protection than doing nothing at all.
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Old 14-12-2007, 20:19   #9
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Where does this huge cable live while you're not in a lightning storm? Can you clear your fair leads, jib sheets, halyards when it's at the base of the mast? As that fella pointed out, the cable size you'd need will be considerable. It will weigh a hundred pounds.

When under sail, at what point do you leave the helm and begin to gather up all DC connected electronics to store in the oven? How many disconnects, bracket disassembly ets? How much time will this take? Who's at the helm?

I guess I'm doing a poor job of making a point. When things go bad, they go bad quickly. You don't have as much time as you think to accomplish all these tasks as you're trying to steer your boat.

Sea water doesn't conduct electricity very well. Head toward deeper water at the onset of a storm and you won't get hit.
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Old 14-12-2007, 22:06   #10
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Rick,
I was talking about two small portable items, as you can kiss all the fixed stuff good bye after a direct strike !!
Don't know about your boat, but I have easy access to the foot of my mast with a clear path strait through the bottom of the bridge deck.
It is essential that cable cross sectional area is sufficient, typically 35mm or greater. (Hence aluminium for lightness and corrosion) 100lbs ???
You are correct, when things go bad, they go bad quickly, but you usually have plenty of time before the onset of a thunder storm, but a prudent sailor will either have things in place or have a system that is quick and easy to implement. Besides, what's an auto-pilot for ?
As for heading for deeper water, I think that can be filed in the urban myth category. Boating in fresh water is far more dangerous as far as lightning is concerned and most forms of lightning protection in fresh water offers little protection. This thread was started to see what methods of LP people apply and how they implement them on catamarans. Lets contribute in a positive fashion.
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Old 14-12-2007, 23:16   #11
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Professional Boatbuilder Magazine has a free online lecture about this. You have to register to take it, but no $$ involved. The gist of the article was that lightning wants to ground to the water's surface around the waterline, so when sailing monohulls put their ground plate under the mast, they are inviting side flashes. Their idea was multiple grounds around the waterline just above the waterline, as well as the standard 1 square foot copper plate, and they suggested grounding lifelines and (metal) bimini frames as well as heavy metal items. They suggested not running a ground wire or strip down the center of the hull as this would also invite side flashes. On a sailboat with metal shrouds and chainplates, I think the logical inference would be to ground each of them to small grounds near the waterline, and to run a ground line around the inside of the waterline, connecting any metal through hulls to it.
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Old 15-12-2007, 02:50   #12
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Mike

Thanks for your informative post.

I am a precision engineer rather than an electrical engineer so my solution below might be a waste of time but your comments would be appreciated.
My idea was to use a copper strap (3/4" x 1/4" or similar) connected to the base of the mast. As the windlass is right beside my solution would be to connect the other end of the strap to the chain plate and have the anchor in the water by about 6" when lightening is a possibility. The anchor should be short enough not to be able to touch either hull but should give you a direct path from the mast to the sea. I'm sure it wouldn't protect any of the electronics on board but it might save any person getting a serious belt. I think the most dangerous scenario is getting holed as the charge has no direct path so at least this would give a fairly direct path. There would be quite a speed penalty dragging an anchor in the water whilst sailing but this system could be easily used when in a marina, anchorage or when you are away from the boat.
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Old 15-12-2007, 03:22   #13
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Originally Posted by Crak View Post
Rick,
I was talking about two small portable items, as you can kiss all the fixed stuff good bye after a direct strike !!
I'm happy to report that all portable electronics survived my lightning hit just fine. They were all sitting on the Salon table. Oven was not required.

On my boat I have 2 forestays, lowers, uppers and a pair of backstays. I believe this affords some level of protection.

I'm going to sign up and watch that video.
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Old 15-12-2007, 03:52   #14
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Quote:
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... I made my living fitting lightning protection to electrical outside plant and I can tell you what works and what is a waste of time...

And George Parker made his living selling New York’s public landmarks to unwary tourists. His favorite object for sale was the Brooklyn Bridge, which he sold twice a week for years.


I thinks it’s important to note that the scientific, engineering, and fire safety communities do not support the theory & practice that Mike and others (primarily purveyors of CTS’s) preach; because the underlying theory lacks scientific credibility, and because every independent study demonstrates that they do not prevent lightning strikes.

The various “Lightning Prevention (LPS), “Charge Transfer” (CTS), “Early Streamer Emission” (ESE), or “Dissipation Array” systems (DAS) have NOT been shown to prevent, or significantly reduce, the probability of a lightning strike. Not in theory, and not in practice.

Despite the evidence (or lack of evidence), they continue to be sold, installed, and promoted.
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Old 15-12-2007, 05:10   #15
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As for heading for deeper water, I think that can be filed in the urban myth category. Boating in fresh water is far more dangerous as far as lightning is concerned and most forms of lightning protection in fresh water offers little protection. This thread was started to see what methods of LP people apply and how they implement them on catamarans. Lets contribute in a positive fashion.
I am contributing best I can, by relating my experience. The problem as I see it is that you disagree with people who do have experience in this area. There are some excellent threads on this forum which have disected lightning and protection systems. You should take some time and read them.

This chart is from one of those threads.

Electrical Conductivity (S•m-1)
Silver 63.01 × 10^6 Highest electrical conductivity of any metal
Copper 59.6 × 10^6
Aluminium 37.8 × 10^6
Seawater 5
Drinking water 0.0005 to 0.05 (fresh water)
Deionized water 5.5 × 10-6

I live in the Lightning Capital of the US, and suffer lightning storms every day during summer months. Hits to boats here and in the Bahamas are a regular occurance. I would love for you to post some data on your statement that boating in fresh water is far more dangerous due to lightning.

As far as Urban Myths go. Where is the data that supports that grounding a boat has lightning protection benefits? Reference Gords posts on this subject.
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