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post #11 of 75 Old 08-21-2008
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post #12 of 75 Old 08-21-2008
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Quote:
Originally Posted by Freesail99 View Post
I was driving in my pick up truck in a terrible lighting and rain storm, when lighting hit the bumper of the car in front of me and then seemed to bounce off of the car's bumper and hit my trucks bumper with a huge flash of light that blinded me. There were burn marks on my chrome bumper.
With all due respect, if both engines kept running and both drivers were still conscious, I don't think that was a true strike from the main bolt, which is what I am referring to (strikes that knock out electronics and damage people/boats/vehicles). I have been near a lightning strike and felt my hair raising and had sparks shoot from my hand to a collapsible fishing rod that was in a bag I was carrying. I was walking across a parking lot with rubber soled shoes; it's like electricity is in the air around the strike point.

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post #13 of 75 Old 08-21-2008
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My research put it this way.
If you properly bond, you increase the chance of hits, but lower the damage if hit.
If you improperly bond (and it's not easy to do it right,) you've made everything worse.
If you don't ground, you've lowered the chance of a hit.

The best idea for non-metallic boats was to get a 30 foot length of 1/2 inch wire. Strip 6-10 foot off each end. Wrap once or twice around the mast and put the ends into the water.

This way your not grounded because of the insulation, but should a hit occur the insulation is irrelevant to lightning and you've provided a ground path.
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post #14 of 75 Old 08-21-2008
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Quote:
With all due respect, if both engines kept running and both drivers were still conscious
When I was in my early 20's, myself along with my wife were knocked unconscious, when lighting hit the wire in a vineyard, we were working in. I am told over 20 minutes when by, before we came too.

As far as the truck is concerned, perhaps the old wife's tale about a car being one of the safest places to be, during a lighting storm, is true. I know it happened and the burn marks were still on the bumper, when I sold the truck.

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post #15 of 75 Old 08-21-2008
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My understanding is that a car is a sort of Faraday cage -- when you are surrounded by grounded metal, a lightning strike is conducted through the outer skin of the cage and anything in the cage is completely untouched. I remember seeing a demonstration of a Faraday cage at the Boston Museum of Science many years ago. I always hoped that the combination of all of the standing rigging and mast would help protect the occupants, but don't have any scientific basis for it. I do know that when I have been caught in a real thunderstorm (last one was in late June, just south of Plum Gut) everything I have ever learned tells me that it is not good to be under a 50 foot piece of aluminum sticking into the sky -- especially since there is nothing else above wave level in the vicinity. I have been scared s**tless, but it hasn't deterred me from sailing.
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post #16 of 75 Old 08-21-2008
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Lightning wants to take the shortest and least resistive path to ground. As people have mentioned, if you ground your boat, you do slightly increase the chance of a lightning strike, if one was going to happen in your general area anyway, since you shorten the path to ground by the height of your mast off the water. Again, this is only a concern if the lightning strike is going to be near you anyway. It all depends on the amount of charge in the air near you. The benefit to grounding your boat and mast, is that the mast creates what is known as a "shadow affect", in that since the mast is the highest point, other points below it, out to a radius roughly the height of your mast, won't get hit. You can still get electrocuted if you are touching metal that is attached to the ground path, or if you offer a better ground path, but if you are just sitting in your cockpit, not touching metal that is part of the ground system the mast is connected to, you should be quite safe. Electricity flows along the outer surface of metal, not through it as most people think. That is due to the physics of electrons on the surface of a metal being easier to "move" then the ones in the metal (Less Resistance). This again gets back to the least resistive path point and explains why you don't get shocked when in your car if a wire or lightning hits it. It also explains why a Faraday cage works.

If you are travelling through a area with highly charged air, and a lightning strike is going to happen, you might get hit slightly more often with a grounded boat / mast, but in that case you want the mast grounded for the protection of the "shadow affect", otherwise the next highest thing that is grounded will get hit. That might be you standing up on the boat touching another surface that is grounded.


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post #17 of 75 Old 08-21-2008
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The other argument I have heard regarding grounding (whether it be a boat or an antenna or whatever) is that a good ground prevents charge buildup. For example, a lightning rod is a sharpened point that allows electrons to stream off rather than accumulate.

The noise the OP heard was probably the electrons streaming off of the mast.

I believe it is a complicated issue that even the "experts" don't totally understand.
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post #18 of 75 Old 08-21-2008
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Quote:
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My understanding is that a car is a sort of Faraday cage -- when you are surrounded by grounded metal ...
The point is that a car is not grounded; it's suspended above the ground by 4 insulators (tires).

-Andy
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post #19 of 75 Old 08-21-2008
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Andy, tires haven't been good insulators for decades now. They're actually pretty good conductors. In the 50's, mobile radio operators used to do odd things to bleed off the static and ground the cars because the static created a huge noise problem. Today? The issue is forgotten, the tire compounds are way different. You don't see many cars or trucks dragging rubber ground straps any more, do you? Not even the fuel trucks.

A strike will still tend to flow over the outside of the car, over the sheet metal, but it WILL go to ground, through the tires if not past them.
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post #20 of 75 Old 08-21-2008
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Hello,

I stand corrected. A few things I believed are not true:
Electrical Safety Myths
The shoes I spoke of earlier probably weren't insulators either.

-Andy
Newport 17 - "Kohanna"
At sea Darwin's hypotheses is the final arbiter of right of way.
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