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Old 14-06-2013, 11:18   #16
Guy
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Re: 2 Dyna Plates

Well you may be going to far with your garlic thing. Aircraft are hit all the time. They have lots and lots of electronic goodies that live another day. Composit aircraft often have a conductive mesh in the lay-up to provide a path back out to the atmosphere. In something like a helicopter which gets a hit on a rotor blade, the charge goes through all the rotating gears, bearings and often out the tail rotor or tail. Often quite a mess. The strikes I've seen are not dramatic just a 1/4" hole in and out again.
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Old 14-06-2013, 11:31   #17
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Re: 2 Dyna Plates

EXACTLY, an aluminum or conductive frame aircraft represents the Faraday shield I was describing, just the opposite of a fiberglass boat. And aircraft manage without a grounding plate .

An Aluminum or Steel boat with a metal deck is a much safer environment. When the boat next to me was hit and the mast wiring set on fire, we had no damage. We are (were) 75 tons of steel with 1/4" steel under the teak deck. However that may have just been a product of the total unpredictability of lightning. Any cables entering or leaving the protected volume are going to introduce damaging voltage spikes. You can bet that things like antennas on aircraft that penetrate the shield are very well protected.
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Old 14-06-2013, 11:47   #18
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Re: 2 Dyna Plates

I completely get the induced current in all nearby conductors. A high di/dt will induce large coupled currents. A large, very inefficient, air-core transformer just as Andina described. The inefficiency is irrelevant due to the levels involved. That's not what I'm talking about. I agree, I don't think electronics or electricals can be protected. I'm concerned with physical damage to the boat's hull due to a primary strike to the mast. With no connection to ground (aka the water), won't the energy simply find it's own path through the hull. Or perhaps even with a ground plate, the energy involved will simply blow holes where the connections to the plate are located. Just trying to give my boat the best odds of staying afloat if struck.
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Old 14-06-2013, 11:47   #19
Guy
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Re: 2 Dyna Plates

Modern aircraft often have lightning dissipators along with static wick dissipators, so they do have a sort of ground. You will have to invent a reason why it's not a good idea to ground your boat to the water. Where by the way, the the damn bolt was headed anyway. I see more resistance in choosing your mast as a pathway to the sea than just going there directly
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Old 14-06-2013, 11:58   #20
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Re: 2 Dyna Plates

Quote:
Originally Posted by Guy View Post
Modern aircraft often have lightning dissipators along with static wick dissipators, so they do have a sort of ground. You will have to invent a reason why it's not a good idea to ground your boat to the water. Where by the way, the the damn bolt was headed anyway. I see more resistance in choosing your mast as a pathway to the sea than just going there directly
The static dissipaters on aircraft are to bleed off static charge. I don't believe they have anything to do with lightning protection.
I think I was not clear. I'm trying to make the case that a ground plate on your mast is a good idea if only to prevent damage to the hull. I'd like to be wrong about this as it would be less stuff I need to add to my boat. A direct strike to the boat really concerns me. Not because of electronics damage, but because it could sink the boat. Compared with a sunken boat, electronics are relatively easy to replace.
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Old 14-06-2013, 12:06   #21
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Re: 2 Dyna Plates

Lightning is too unpredictable to make reliable decisions. My gut feeling is that a small ground plate on the hull connected to upper metal would concentrate the exit energy in one place rather than letting the strike find its own way to the water.

I remember working on overhead telephone lines (over 50 years ago in Australia) and going out on repair runs after a lightning storm. It gave you an insight into the totally unexpected consequences of lightning and how it frequently avoided the logical path. The entry boxes had lightning gaps to a solid ground stake and large cartridge fuses to the phone in the house. On our own home, moisture had penetrated the box and the fuses. A lighting strike vaporized the moisture in the fuse and blew one cap off that went like a bullet through the box and 2 sheet-rock walls.
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