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Old 01-22-2013
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Use a metal swing keel for lightning sink

I actually have a Lightning and wonder if i can wire the aluminum mast to the swing keel for lightning protection?
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Old 01-22-2013
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Re: Use a metal swing keel for lightning sink

You are better off putting a bronze plate or dynaplate I think. Read this thread. Mainesail has one type of setup. I have a Newmar ground shoe

lightning advice
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Old 01-22-2013
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Re: Use a metal swing keel for lightning sink

There's been recent suggestions from research that the 'sink/ground' for lightning shouldn't be deep 'underwater' but rather at the water surface. Some are advocating 'waterline' dissipators and electrodes: Marine Lightning Protection Inc.

Noone really knows, Ive been 'hit' three times on different boats ... it all remains a 'crap shoot'.
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Old 01-22-2013
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Re: Use a metal swing keel for lightning sink

Quote:
Originally Posted by RichH View Post
Noone really knows, Ive been 'hit' three times on different boats ... it all remains a 'crap shoot'.
I think emphasis on Crap.... because I know something like that would scare it out of me.
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Old 01-22-2013
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Re: Use a metal swing keel for lightning sink

Dynaplates and "Grounding shoes" WILL NOT WORK AS LIGHTNING GROUNDS.

The reason, Remember basic Electricity and Magnetism in physics? The electric field within a closed conductor is zero. This means that at high values of E field (Lightning), the field simply bridges the pores of the plate giving only the external area to dissipate the current.
At low values of E (low current typical of radios etc), the field does NOT bridge the pores so it acts as if it has a huge surface area.

For a lightning dissipating ground, you really do want a large external area and as much "external" edge as possible. The field is highest at the edge and that is where the current will go.

Yesterday, somebody posted a pic of what I think is a good lightning ground, it was a narrow long strip on their outside hull. However, it looked as if it was painted. Be careful, some anti-fouling paints do not conduct and you want it to readily conduct

So, as long as you keep your metal centerboard painted with CONDUCTING paint, it'll work cuz it has lots of surface area. I'd worry about using the CB pin as your contact though.

The reason for wanting your lightning ground close to the surface is for two reasons and I am not sure they make sense :

1. Analogy to the E field within a conductor (Yeah seawater is a good conductor for most low frequencies) says the field there should be zero so it seems like no current would flow. Not true, remember that in a VAn de Graff generator the charge is brought to the INSIDE of the big hollow HV terminal and then it simply goes to the surface. I do not think this reason makes sense.

2. High frequency "skin effect" whereby high freq components of the lightning pulse travel best on the surfaces of conductors. Maybe, maybe, maybe.

My lightning ground on my sailboat (up till now) was a 2' X 2' copper sheet (flashing) with a copper bolt/clamp/soldered to a tinned #00 insulated Ancor cable 15' long with a good welders clamp to attach as high as I can on the mast to avoid bends of the wire. During a storm, the plate gets dropped overboard and the clamp goes on the mast. A Nylon rope keeps the plate from being dragged backwards to ward the prop and I maintain only steerage speed. Yes, I am paranoid of lightning.
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Old 01-22-2013
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Re: Use a metal swing keel for lightning sink

A Dynaplate as a lightning ground is outright dangerous, and they're the first ones who'll tell you so. Dynaplate is made from sintered bronze in order to provide greater contact area (much much greater) than a simple plate. If it takes a strike, all the water that is filling the voids in the sintered metal instantly flashes over into superheated steam, producing an explosion.

Not a good thing.

So by all means, a solid plate would beat nothing. Using the swing keel probably is better than nothing (or a Dynaplate (G)) but how effective it would be would depend on whether you could make a fairly straight cable run or not, and how much resistance was in the swing pivot.

Of course with a boat that small you always have the option of the best lightning protection in the world: Invert the boat and come back after the storm.
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Old 01-22-2013
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Re: Use a metal swing keel for lightning sink

For a Lightning, the best thing might be to simply drape a conductor (jumper cables?? a chain??) from the upper shrouds into the water when you're moored. Mooring next to a boat with a taller mast might work too. You aren't likely to purposely head out into thunderstorms, so you probably don't need anything set up when you're sailing the boat. You certainly could re-rig your conductor if a storm came up while you were out; it's just a good bit of drag otherwise. I've been out in Lightnings in some nasty thundersqualls. Taking down the sails and moving aft in the cockpit (away from the rigging and centerboard) seemed to work well enough. As mentioned above, for a grounding plate you want as much surface exposed to the water as possible. This would indicate having the centerboard down all the way. Leaving the centerboard down on a moored Lightning is a sure-fire way to capsize it at the mooring: I have seen it happen at Larchmont Race Week. A squall comes through with a new wind direction, and because the board is down, the boat can't swing fast enough to head into it. The gusts hit the boat and mast broadside, the board keeps the boat from turning, and with no ballast (crew) to counter it, the windage knocks the boat over. Friends of ours have been hit by lightning, but they were on bigger keelboats.
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Old 01-23-2013
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Re: Use a metal swing keel for lightning sink

Quote:
Originally Posted by Frogwatch View Post
My lightning ground on my sailboat (up till now) was a 2' X 2' copper sheet (flashing) with a copper bolt/clamp/soldered to a tinned #00 insulated Ancor cable 15' long with a good welders clamp to attach as high as I can on the mast to avoid bends of the wire. During a storm, the plate gets dropped overboard and the clamp goes on the mast. A Nylon rope keeps the plate from being dragged backwards to ward the prop and I maintain only steerage speed. Yes, I am paranoid of lightning.
Have you ever considered a "trolling plane" (for lack of a better word) when I was younger, friends used to take their boats out fishing. They always had these two stainless steel "planes" that had hooks attached to them. They would toss them overboard the stern and the speed of the boat would pull them straight down.. untill a fish grabbed a hook and then it would allow the rope attached to it to slide forwards and they would ascend.

I think something similar would work for you.. just make it so it cannot ascend on it's own and unless you want fried fish for dinner, do not put hooks on it
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