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post #11 of 16 Old 08-01-2010
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Originally Posted by Jeff_H View Post
Actually, almost nothing is more scary to me than to be on a steel boat in a lightning storm.
There is no guarantees with lightening, but a metal boat is safer than a non conductive material, such as fiberglass.
The metal provides a good ground (which is sometimes added in fiberglass boats with thick wiring to reduce the damage associated with a strike) and the conductive nature of the hull material provides a faraday cage that protects crew below.
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post #12 of 16 Old 08-01-2010
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Lightning seems to be totally random. Here on Lake Huron we get a huge number of lighting bolts a year and often while racing have dozens and dozens of boats out in storm. It totally amazes me that more boats do not get hit. I hear of maybe 2-3 per year.
Typically it just fries the electronics. It can be much worse, rarely are there injuries although a few years ago a helmsman was burnt as the bolt transferred down the back stay. Years ago an Alberg 37 was hit and a friend who saw it after they raised it said the hull looked like it had been hit many times by a shot gun blasts.

Stay away from the metal parts and "hope for the best" My view is a well grounded boat is your best defence although I tend to believe you are more likely to get hit in one.

Lighting does not vary very far off it's intended path. One year in a thunder storm I felt a blast of heat and smelled very strong ozone. That is about as close as I want to get to a strike
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post #13 of 16 Old 08-01-2010
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Originally Posted by Jeff_H View Post
Actually, almost nothing is more scary to me than to be on a steel boat in a lightning storm. A lightning strike on a steel boat is especially dangerous. The large voltage through the steel can literally electric arc cut the plating and can instanteously eletrolysize away sections of the hull. I looked a steel boat that had was being salvaged in South Florida years ago and a large chunk of the bottom plating looked like swiss cheese. The owner was badly burned and one of the crew was left in critical condition after receiving a major shock thought to be from induced current through a portion of the hull.

web page:
or pdf file:

[Note these are EXCERPTS ONLY. And there's also info on electronics.]

There is no such thing as lightning-proof boats, only lightning-protected boats. All-metal ships are rarely damaged, and injuries or deaths are uncommon. These ships are frequently struck, but the high conductivity of the large quantities of metal, with hundreds of square yards of hull in direct contact with the water, causes rapid dissipation of the electrical charge.
I also had an afternoon with a wonderful and very experienced compass adjustor who worked the east coast of the US and his stories seemed to back up my personal experience that if you are going to be struck ,a steel boat with an ali mast was the way to go.

I was inside the cabin and not touching anything metallic when the strike happened. I suspect that had I been on deck the risk of injury would have been higher but again the experts say the lecky will take the path of least resistance soooooo I think the hull gets it and not the crew member.

Oh yeah the adjustor was onboard to drive out the evil spirit [magnetism] that had taken up residence. It looked like Balinese ritual dancing and some Tai Chi as he herded the spirits into corners and drew them off into space. All for a six pack too !

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post #14 of 16 Old 08-02-2010
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In his book Sailboat Electrics Simplified, Don Casey has a succinct write up about boats and lightning. Included is a good discussion on proper bonding techniques (separate the lightning and electrical system grounds, easier said than done). Stray currents damage electronics if the grounds are tied together. It’s like arc, MIG, or TIG welding on a steel hulled vessel without disconnecting the electronics.

I’ve worked on a few antenna installations on buildings with coax isolators installed. One installation worked great, a crispy black antenna with no other damage. The other installation wasn’t so lucky, blown out TV, computer, etc. A lot of the randomness is likely due to directness of path, quality of connections, corrosion at terminals, size of conductors, etc.

Even if a boat is grounded properly, I think it would be more at danger on dry land. I’ve seen photos of boats in boatyards that had holes blown in the bottom of the hull because the lightning was desperately trying to get to ground. In the same vein as dragging a chain through lakes, if the boat will be stored on the hard it’d make sense to ensure a direct path to ground with a chain, cable, or wire.
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post #15 of 16 Old 08-16-2010
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If you have a wooden spar, a direct hit down the mast will generally cause the mast to split / explode as the water is superheated and expands with the heat. You can rig a temporary lightening rod, or put a permanent rod up that connects to the main track, then run a thick cable from the track to something metal in the water that you're okay with passing a ton of current through.

Keep the water on the outside, you on the inside, and the stick in the air.

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post #16 of 16 Old 08-19-2010
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Grounding of metal parts

It is certainly intimidating when a thunderstorm starts to head your way. Once looked up for a weird sound aboard my commercial fishing boat and watched as an antenna started to "sizzle" as a storm approached . Other than that instance (got the H out of there fast), have never had a run-in with a bolt of lightning although through many storms over the years. It seems to me that being hit is probably as random an event as it is on land. I guess the theory is to make your boat's potential the same as the sea by grounding it to the water, giving the electricity no reason to be attracted to your spot. I do not understand this at all because the boat is above the surface of the water and would seem, logically, to be a target just BECAUSE it is connected to the water and hence a higher strike point way up there at the masthead. One thing I do when a storm is coming is to completely detach my electronics from antennas/batteries/grounding...everything. This way if I do get hit, at least I may still have some communication capability. It also saves a lot of expensive gear from melting down all at once which has happened to more than one sailor I know.
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