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Old 18-01-2012, 01:00   #1
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A Gemini's Friday the 13th Lightning Strike

My old friend Larry and his girlfriend Dana Jean were anchored on sv Dana Jean a Gemini 105M at Treasure Cay in the Bahamas last Friday night, at 3:00 AM a big Booooom !!! they and 2 other sailboats were hit by lightning. No holes in there or the other boats, there cat was the worst hit all the brakers were a smoldering heap, there refrigerator is toast it cooked three radios, CPS, light fixtures, the disel's altinator, radar, and who knows what else. He does have insurance and his I phone works but to get things repaired in anthor country may be a problem. I'll keep up dating.
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Old 18-01-2012, 06:37   #2
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Re: A Gemini's Friday the 13th lightning strike

That's a bummer. We have good cruising friends who had their gem struck while on their boat lift here on the mid-Chesapeake. Same sort of damage, including some hull damage (no hole, though). Insurance covered it sans deductible. There's some long discussions on the Gemini_Cats Yahoo group on grounding/not grounding...good arguments on both sides. I still can't understand how out of a large group of boats, the ungrounded boat with the shortest mast can be the one struck by lightning (different story)...lightning is weird stuff.Hope your friends can get ship-shape without it ruining their voyage.
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Old 18-01-2012, 06:45   #3
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Re: A Gemini's Friday the 13th lightning strike

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Originally Posted by Waterway Guide View Post
That's a bummer. We have good cruising friends who had their gem struck while on their boat lift here on the mid-Chesapeake. Same sort of damage, including some hull damage (no hole, though). Insurance covered it sans deductible. There's some long discussions on the Gemini_Cats Yahoo group on grounding/not grounding...good arguments on both sides. I still can't understand how out of a large group of boats, the ungrounded boat with the shortest mast can be the one struck by lightning (different story)...lightning is weird stuff.Hope your friends can get ship-shape without it ruining their voyage.
IF either the drive leg was dipping into the waves or the chain was down, they were grounded. Do we know? Being "non-grounded" bouncing around in a thunderstorm is a little difficult. Even a lift has wet, salt impregnated straps.

and lightning is unpredictable.
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Old 18-01-2012, 07:08   #4
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Re: A Gemini's Friday the 13th lightning strike

I thought you want to be grounded so all that energy has a nice short path out of your boat to earth?
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Old 18-01-2012, 07:39   #5
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Re: A Gemini's Friday the 13th lightning strike

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IF either the drive leg was dipping into the waves or the chain was down, they were grounded. Do we know? Being "non-grounded" bouncing around in a thunderstorm is a little difficult. Even a lift has wet, salt impregnated straps.

and lightning is unpredictable.
Sorry if I wasn't specific - I mean't "a lightning ground system installed" where the mast and rigging is grounded to a plate on the hull, hopefully protecting the vessel and components from damage.
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Old 18-01-2012, 08:00   #6
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Re: A Gemini's Friday the 13th lightning strike

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Sorry if I wasn't specific - I mean't "a lightning ground system installed" where the mast and rigging is grounded to a plate on the hull, hopefully protecting the vessel and components from damage.
I understood you.

What I meant to question was the idea that NOT grounding a boat reduces the chance of strike. My belief, right or wrong, is that it is not practical to isolate a boat, floating on saltwater in the rain, completely enough for it to make a difference to lightening. The charge has already jumped thousands of feet to the masthead; a few feet or inches of salt-covered rope and fiberglass are not going to make a difference. The boat is still projecting ground potencial to the masthead.

Further, if the anchor chain, drive leg, or outboard are in the water, you are absolutly grounded, just not in a protective manner.

Can a lightning protection system really work? I'm intentionally not touching that, as it is a very complex subject.
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Old 18-01-2012, 08:36   #7
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Re: A Gemini's Friday the 13th Lightning Strike

Yeah, I'm with you. The arguments that are most interesting are whether properly grounding a boat is more likely to attract lightning, and whether the grounding system is likely to protect the boat much more than not having the system if it is struck. I'm first to say that I don't have a clue! (I have not installed a grounding system). I'm sure there's some good discussions in CF too.
For a Gem, not too many of us use all chain, and if one does, it's not connected by metal to the mast or shrouds. The drive leg isn't connected to much either. From what I've read, the worst damage seems to be done by the current trying to find a way from the mast/shrouds to the water, and frying everything in the process. Make's you wonder whether lifting the drive leg might make a difference..who knows?
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Old 18-01-2012, 09:25   #8
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Re: A Gemini's Friday the 13th Lightning Strike

this is another one of those many things I have no first hand experience with, despite a long career working with electronics and electrical systems on a variety of boats. my opinions, after a lot of thought and some electrical experience around grounding systems on boats, ...

Your sailboat is essentially already grounded as far as lightning is concerned. All that metal that close to salt water, with salty ropes and lines and decks and canvas. Lightning thinks nothing of leaping gaps much bigger than your freeboard. the thing is, that normally lightning is not happening directly overhead of your boat. The geometry usually puts the nearest ground (the ocean, typically) closer to the lightning than you are. Lightning hits the water because it's closer than you are to it.

BUT in cases where lightning is formed right over you, you're the shortest path to ground.

What a properly grounded boat does is to establish a ground path for all the major components on the boat directly to ground without the electricity having to pass through a circuit that other equipment is connected to. Whatever the lightning hits, you want it to be able to go from there directly to ground without energizing your entire ac wiring in the process. In this way, whatever took the hit is toast, but you should be able to save most of the other stuff that wasn't sitting right next to the strike.

When you hear a lightning story that includes " then took out everything on the boat", I am thinking that was not a properly grounded setup.

When I was doing hi resolution seismic work we frequently used large, triggered capacitor banks to supply a big-azz pulse of several kilojoules to some acoustic seismic sources behind the boat. Some of these sources, called spark-arrays, are basically big frames with electrodes isolates within them. The pulse, say 6-9 Kilojoules (watt seconds per second) throws a blue spark across that underwater array that you wouldn't believe. It's micro lightning. Very pretty. Can see it for miles. Makes a big noise, that is then used to determine what's under the sea bed. Different monologue than this one.

At the same time that we were charging up the caps and hitting the water with this huge spark, sensitive hydrophones and navigation and bathymetry equipment must also be able to work on the same ship/generator electrical system that is generating the spark. proper grounding became routine, as it was absolutely vital. We ran a thick ground cable from the lug on every single piece of equipment to a common lug on a ground plate which was grounded to the sea. Quite often it was a fixture on a steel hull, but we made sure it was a bolt or something right near the water, and grounded to the water. I.e. Not painted. Also, we needed an exposed patch of hull in the water. Not that easy to find. You don't want the prop shafts, rudder shafts, or zincs to be the spark points. Easiest to dedicate a piece of copper cable or steel plate. We did NOT link or daisy chain grounds from one system to the next.

I think the best approach to any boat would follow those same guidelines. you cannot determine whether or not lightning will hit your boat in a storm. That's random position. What you CAN do is minimize the damage by getting the lightning to take a path you define, which bypasses all the stuff susceptible to damage.

It's the electrical equivalent of digging a rain trench around your tent, and over to the creek to control runoff in a heavy downpour.
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Old 18-01-2012, 10:40   #9
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Re: A Gemini's Friday the 13th Lightning Strike

From what I have read grounding plates of copper you would need to ground a boat would be too big to be what you would want to carry around crusing. I just hope my buddy will get his boat fixed up so we can go crusing with them, as he had just called and invited us to come stay for a couple of weeks.
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Old 18-01-2012, 11:11   #10
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Re: A Gemini's Friday the 13th Lightning Strike

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From what I have read grounding plates of copper you would need to ground a boat would be too big to be what you would want to carry around crusing.
Not so much. The National Electrical Code (NEC) specifies 1 square foot for lightning grounding in salt water. This can be easliy managed with a plate or by trailing 2 x 10' cables (the area required is less if there is a long edge, since a greater area of water is acessed). In freshwater the reqiurment is about 10x greater (I forget) and may be impractical.
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Old 18-01-2012, 11:26   #11
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Re: A Gemini's Friday the 13th Lightning Strike

Wow, that's a bummer. There are so many discussions regarding grounding it's silly. No one knows. People on a golf course get hit near a tree 10 times their height. it's electricity on a fast path, not predictable, often branching into several bolts near the ground point. If you are grounded and it hits your mast, it may jump several places before one branch goes to your ground plate.... the other bolts fry everything else... My Passport 47 was hit in Annapolis, fried the little windvane on the mast top and the tricolor lense, blackened the white paint at the both sides at the upper shroud attachment. No other damage to electronics at all... not grounded. I guess it must have leapt from the uppers to the water from the chainplates...
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Old 18-01-2012, 11:30   #12
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Re: A Gemini's Friday the 13th Lightning Strike

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Originally Posted by Canibul View Post
this is another one of those many things I have no first hand experience with, despite a long career working with electronics and electrical systems on a variety of boats. my opinions, after a lot of thought and some electrical experience around grounding systems on boats, ...

Your sailboat is essentially already grounded as far as lightning is concerned. All that metal that close to salt water, with salty ropes and lines and decks and canvas. Lightning thinks nothing of leaping gaps much bigger than your freeboard. the thing is, that normally lightning is not happening directly overhead of your boat. The geometry usually puts the nearest ground (the ocean, typically) closer to the lightning than you are. Lightning hits the water because it's closer than you are to it.

BUT in cases where lightning is formed right over you, you're the shortest path to ground.

What a properly grounded boat does is to establish a ground path for all the major components on the boat directly to ground without the electricity having to pass through a circuit that other equipment is connected to. Whatever the lightning hits, you want it to be able to go from there directly to ground without energizing your entire ac wiring in the process. In this way, whatever took the hit is toast, but you should be able to save most of the other stuff that wasn't sitting right next to the strike.

When you hear a lightning story that includes " then took out everything on the boat", I am thinking that was not a properly grounded setup.

When I was doing hi resolution seismic work we frequently used large, triggered capacitor banks to supply a big-azz pulse of several kilojoules to some acoustic seismic sources behind the boat. Some of these sources, called spark-arrays, are basically big frames with electrodes isolates within them. The pulse, say 6-9 Kilojoules (watt seconds per second) throws a blue spark across that underwater array that you wouldn't believe. It's micro lightning. Very pretty. Can see it for miles. Makes a big noise, that is then used to determine what's under the sea bed. Different monologue than this one.

At the same time that we were charging up the caps and hitting the water with this huge spark, sensitive hydrophones and navigation and bathymetry equipment must also be able to work on the same ship/generator electrical system that is generating the spark. proper grounding became routine, as it was absolutely vital. We ran a thick ground cable from the lug on every single piece of equipment to a common lug on a ground plate which was grounded to the sea. Quite often it was a fixture on a steel hull, but we made sure it was a bolt or something right near the water, and grounded to the water. I.e. Not painted. Also, we needed an exposed patch of hull in the water. Not that easy to find. You don't want the prop shafts, rudder shafts, or zincs to be the spark points. Easiest to dedicate a piece of copper cable or steel plate. We did NOT link or daisy chain grounds from one system to the next.

I think the best approach to any boat would follow those same guidelines. you cannot determine whether or not lightning will hit your boat in a storm. That's random position. What you CAN do is minimize the damage by getting the lightning to take a path you define, which bypasses all the stuff susceptible to damage.

It's the electrical equivalent of digging a rain trench around your tent, and over to the creek to control runoff in a heavy downpour.
Grounding the boat won't protect your electronics. The electromagnetic pulse will generate voltages and currents in electronic circuits beyond what they can handle.

The way to protect electronics is to put them in a metal box. (Faraday cage)

What grounding MIGHT do is prevent the lightning from blowing holes in the boat on it's way to ground.
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Old 18-01-2012, 11:50   #13
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Re: A Gemini's Friday the 13th Lightning Strike

The geometry usually puts the nearest ground (the ocean, typically) closer to the lightning than you are. Lightning hits the water because it's closer than you are to it.

BUT in cases where lightning is formed right over you, you're the shortest path to ground.

Great post, but keep in mind that lightening doesnt take the most direct path to ground.... just watch the horizontal bolts on the evening news!
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