Lightning strike

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northerncaller
Posts:15
Joined:Sun Sep 22, 2013 7:06 am
Lightning strike

Post by northerncaller » Sun Sep 21, 2014 5:12 pm

Hi

Just returned (mid September 2014) from a trip to the Channel Islands, where there was a lot of thunderstorms, although fortunately in the distance and also when we were in a marina with many boats with higher masts! My crew asked, a bit less than casually I thought and with the ice rattling nervously in her gin and tonic, whether there were any preventative measures we could take if caught out in one of these forces of nature and I have to admit my answer was inadequate. I know there's been a lot of discussion on the topic but a definite answer to the problem seems illusive.

It seems to me also that the Ballad is particularly vulnerable because the mast is keel-stepped. In other words any lightning strike on the mast will go straight through the keel. There seems little opportunity, then, to earth the electricity to water.

I'd be very interested in any views on this topic, if for no other reason than I might be able to get this particular crew to sail with me again!

Cheers!

Mike ;)

Bob McGovern
Posts:283
Joined:Fri Oct 26, 2012 3:08 am
Location:Wyoming, USA

Re: Lightning strike

Post by Bob McGovern » Sun Sep 21, 2014 9:43 pm

David Lynn (S/V Nine of Cups, justalittlefurther.com) wrote a story for the most recent Good Old Boat magazine where he claims the proven best lightning prevention technique is standing on one foot, patting your head, and rubbing your belly (all at the same time). Using this method their boat has never been hit by a direct strike.

But seriously, it may be as clever as any other strategy. When you are dealing with several thousand amps and several hundred million volts, anyone claiming to know what lightning will do or how to make it behave is lying thru their scorched teeth. And the competing camps will all insist they are right: You want a fat, straight, single path to the keel. No, you want multiple smaller paths to many grounding plates. No, you want to isolate the mast and rigging entirely from the grounding potential, so it is a resistor & lightning will ignore it.

Nothing new, BTW -- it is an argument dating back at least to the mid 18th century. :D Toss in the various gaizmos sold to nervous sailors (dissipators, voltage clamps, etc. etc.) and consensus best practise wafts even further away.

First thing to consider is how many sailboats there are in the world, most with tall metal sticks on them, parked in moist flat areas, yet how few of them actually take a strike that causes structural damage or injury. Golf is more attractive to lightning than sailing. ;)

Second thing to note is that some sailboats DO take direct strikes that result is structural damage. I know of at least two that had holes blown thru their hull while parked on dry land with the mast down. Nearby boats, on land or water, with spars erect were untouched.

Third thing: Lightning will do whatever it pleases, and you cannot stop it. There are some ways to minimize your exposure to lightning, some ways to direct a small bolt with some degree of confidence, some ways to protect crew and individual components (spare GPS units, handheld VHF). But in the end I'd suggest you might take an actuarial view rather than a engineering view. Your odds of getting hit by lightning on a given sail, or in your sailing lifetime, are probably less than your odds of being killed by a falling tree. And there is precious little evidence anything you do to lightning-proof your boat will make a whit of difference should that one thunderbolt with "Gancia Girl" written on it come knocking. Another round of gin and tonics may be the best approach. "Here -- these cocktails have proven lightning-deterrent effects. I've been drinking them for years. But you have to use Gordon's gin, or all bets are off."

northerncaller
Posts:15
Joined:Sun Sep 22, 2013 7:06 am

Re: Lightning strike

Post by northerncaller » Mon Sep 22, 2014 6:39 am

Brilliant Bob! :lol:

Nicholas Koligiannis
Posts:22
Joined:Wed Sep 25, 2013 12:51 pm

Re: Lightning strike

Post by Nicholas Koligiannis » Wed Nov 05, 2014 5:18 pm

Bob, I agree with everything you've mentioned. But as far as gin goes, I stick to Hendrick's.

Nicholas

Bob McGovern
Posts:283
Joined:Fri Oct 26, 2012 3:08 am
Location:Wyoming, USA

Re: Lightning strike

Post by Bob McGovern » Wed Nov 05, 2014 10:47 pm

Nicholas Koligiannis wrote:Bob, I agree with everything you've mentioned. But as far as gin goes, I stick to Hendrick's.

Nicholas
Okay, Nicholas -- but if Moments is struck by lightning, you will know why! Wrong gin. :lol:

It may be worth building a simple Faraday cage to store certain items in. I could see a small (15cm on a side?) metal box or cage for a digital watch, a handheld GPS unit, a handheld VHF, and the celestial calculator if you use one. The EMP of a nearby strike is similar to a nuclear blast, and even electronics that are not directly hooked to your power system can be damaged. A Faraday cage should (should) preserve these few essentials. Some people keep their expensive or delicate gadgets in the oven or microwave for that reason, tho you can anticipate what might go wrong with that arrangement....

"I'm preheating the oven for cookies. By the way, where have you hidden the sextant?"

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