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Old 25-11-2014, 14:26   #61
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Re: Hit by lightning this afternoon in Botany Bay

It may make more sense to ground all shrouds thus giving several paths.
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Old 25-11-2014, 14:28   #62
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Re: Hit by lightning this afternoon in Botany Bay

Side flashes? GTF out of the way and you won't get hit. Really. If you sit or stand between two possibly ground paths...you're asking for it. On a small craft, sometimes there's no "away" to get to. Which is why you want to encourage the lightning to take one direct path down, by proper grounding and isolation procedures.


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"Lightening just doesn't seem to follow logic, at least as we perceive it." You know, my dog just KNEW that there could be steak every night, according to her perception of logic. You know, steak came out of the kitchen last night, so it could come out again this night, right?
Lightning follows rules of physics. Follows logic. We're just too dumb to figure those out in detail yet. (Same way my dog doesn't understand finance or supermarkets.)
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Old 25-11-2014, 14:43   #63
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Re: Hit by lightning this afternoon in Botany Bay

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Originally Posted by Cadence View Post
It may make more sense to ground all shrouds thus giving several paths.
If you are a lightning worrier, yes, chainplates all the way to the waterline!
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Old 25-11-2014, 14:54   #64
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Re: Hit by lightning this afternoon in Botany Bay

I hope Sweet Chariot was able to haul out and check his damages....and that he gets back to us about it.

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Old 25-11-2014, 15:02   #65
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Re: Hit by lightning this afternoon in Botany Bay

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If you are a lightning worrier, yes, chainplates all the way to the waterline!
I've never worried about it. Wires from the chain plates to ground might form somewhat of a protection zone, onboard under the shrouds?

Why worry about the little things?
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Old 25-11-2014, 15:09   #66
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Re: Hit by lightning this afternoon in Botany Bay

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I also seem to recall some very negative reports about what can happen with ground plates in a lightening strike but cannot recall the issue. Any comments on this?
I think you may be confusing lightning ground plates, which are generally solid bronze with a long length of edge surface with sintered bronze plates that are used for radio grounds.

The sintered plates have had negative reports of exploding during lightning strikes because the lightning flash steams the water inside all the small pores.

The lightning bond system should not be connected to one of those plates.

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Old 25-11-2014, 15:39   #67
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Re: Hit by lightning this afternoon in Botany Bay

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I had my pickup truck hit while driving down the road. Why? Wrong place at the wrong time? I didn't feel a thing. Guess I'm just a lucky SOB.
You were the beneficiary of skin effect. Inside an enclosed metal box the charge is on the surface while the interior stays neutral. Called a galvanic cage. Now if you had been driving a Corvette it might have been a different story.
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Old 25-11-2014, 15:39   #68
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Re: Hit by lightning this afternoon in Botany Bay

Our boat does have a wide copper strip all the way around the inside of the hulls at the waterline. Originally, everything on the boat was grounded to it. A lot of those have gotten broken or gone missing. I bought one of those decent Ancor crimpers and have been replacing and repairing every busted ground wire I can find.
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Old 25-11-2014, 16:04   #69
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Re: Hit by lightning this afternoon in Botany Bay

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You were the beneficiary of skin effect. Inside an enclosed metal box the charge is on the surface while the interior stays neutral. Called a galvanic cage. Now if you had been driving a Corvette it might have been a different story.
I believe you're right. I saw it hit the hood, killed the engine. Fried the wiring.

Traded the truck.

I wonder were it exited?
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Old 25-11-2014, 16:20   #70
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Re: Hit by lightning this afternoon in Botany Bay

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I think you may be confusing lightning ground plates, which are generally solid bronze with a long length of edge surface with sintered bronze plates that are used for radio grounds.

The sintered plates have had negative reports of exploding during lightning strikes because the lightning flash steams the water inside all the small pores.

The lightning bond system should not be connected to one of those plates.

Mark
Exactly. Dynaplate is the brand of sintered bronze ground I'm familiar with and have heard of them being used for grounding the boat.
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Old 26-11-2014, 11:28   #71
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Re: Hit by lightning this afternoon in Botany Bay

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One big difference is towers and steel framed buildings have a lot more steel IE path to ground and are also very well grounded so power goes easily and directly to ground. Sailboats have a much smaller and usually more convoluted path to ground hence the random nature of the results. I have read reports of boats bonded and grounded that the current did not follow the direct path to ground and boats unbounded that had the strike mostly exit the through hulls.
I disagree. Concrete is a terrible conductor. Tall buildings are very well grounded because they have huge copper strips that run down them to ground. Sailboats are also very well grounded relative to, say, a low-lying motor boat with no metal spikes sticking up in the air.

I think the reason it's so unpredictable on a sailboat (but not a building) is that sailboats are relatively short. Since the lightning already has sufficient voltage to arc through several hundred feet of air (it takes about 3,000,000V to arc through 1m of air) the last 50 or so feet of relative conductance offered by a sailboat mast are relatively insignificant, so it is more likely to go all over the place. A tall building, however, offers an easier path for several hundred feet. The voltage required to strike it (under the same conditions) is hundreds of millions of volts less than what is required to strike a sailboat, but the damage is less and because it offers a relatively easy path to ground the path of least resistance is more likely to be followed.

Nevertheless, when it strike a sailboat the lightning must find a path to ground. Few people suffer mast damage from strikes beyond perhaps a bit of scorching at entry and exit points because they are good conductors. Most of the damage is to insulators (when you're dealing with millions of volts, a piece of electronics with tiny-guage internal wiring can be considered to be an insulator, as can anything made of fibreglass). Hence, it follows logically that the best thing to do is to provide an easier path to ground than, say, out of your boat through the fibreglass at the waterline.

This is, of course, conjecture, but it is grounded in logic.......... i think!
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Old 26-11-2014, 11:30   #72
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Re: Hit by lightning this afternoon in Botany Bay

Oh, and the thing with the car? Classic Faraday's Cage. The saying that you're safe in a car because it has rubber tires is nonsense. You're safe in a car because it's a cage of metal, which is a much better conductor than you. A couple of inches of rubber and air are not going to stop lightning from getting to ground!
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Old 26-11-2014, 11:50   #73
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Re: Hit by lightning this afternoon in Botany Bay

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Oh, and the thing with the car? Classic Faraday's Cage. The saying that you're safe in a car because it has rubber tires is nonsense. You're safe in a car because it's a cage of metal, which is a much better conductor than you. A couple of inches of rubber and air are not going to stop lightning from getting to ground!
I think your right again. It went around me and jumped to ground. So quick I didn't even have to change my draws.
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Old 26-11-2014, 12:31   #74
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Re: Hit by lightning this afternoon in Botany Bay

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I disagree. Concrete is a terrible conductor. Tall buildings are very well grounded because they have huge copper strips that run down them to ground.
Certainly concrete is a terrible conductor. So is the glass that most newer building use for the skin but all of them have a huge steel frame inside so why would they need copper as well. If built on concrete piers then maybe some kind of connection to ground from the steel frame.


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I think the reason it's so unpredictable on a sailboat (but not a building) is that sailboats are relatively short. Since the lightning already has sufficient voltage to arc through several hundred feet of air (it takes about 3,000,000V to arc through 1m of air) the last 50 or so feet of relative conductance offered by a sailboat mast are relatively insignificant, so it is more likely to go all over the place. A tall building, however, offers an easier path for several hundred feet. The voltage required to strike it (under the same conditions) is hundreds of millions of volts less than what is required to strike a sailboat, but the damage is less and because it offers a relatively easy path to ground the path of least resistance is more likely to be followed.

Nevertheless, when it strike a sailboat the lightning must find a path to ground. Few people suffer mast damage from strikes beyond perhaps a bit of scorching at entry and exit points because they are good conductors. Most of the damage is to insulators (when you're dealing with millions of volts, a piece of electronics with tiny-guage internal wiring can be considered to be an insulator, as can anything made of fibreglass). Hence, it follows logically that the best thing to do is to provide an easier path to ground than, say, out of your boat through the fibreglass at the waterline.

This is, of course, conjecture, but it is grounded in logic.......... i think!
All sounds like reasonable conjecture to me but at this point I think even the experts are still conjecturing? I took a class at UF from Martin Uman, if not the best then one of the top lightening experts in the world. Attended one of his lectures on lightening and have read a number of his articles. All very interesting and gets very technical.

Last time I looked into the subject I think some related company offered some solutions for protecting things like small buildings, homes, even boats but they were very expensive and came with no guarantee.
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Old 26-11-2014, 14:09   #75
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Re: Hit by lightning this afternoon in Botany Bay

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Certainly concrete is a terrible conductor. So is the glass that most newer building use for the skin but all of them have a huge steel frame inside so why would they need copper as well. If built on concrete piers then maybe some kind of connection to ground from the steel frame.
Indeed they do; i'd neglected that........ I imagine the steel frame must make a big difference. I do know though that i've been up several buildings that have external copper strips as lightning conductors. St. Paul's Cathedral in London springs to mind. My ex-girlfriend was a civil engineer and her twin sister is an architect, so i spent a lot of time examining buildings whether i wanted to or not! St. Pauls Cathedral, however, wasn't built with a steel frame, which may explain the need for the copper. It does, however, get struck quite a bit and hasn't yet suffered any major damage over the last 300 years, from lightning at least. Bombs during the war are another matter entirely!
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