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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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1980 Pacific Seacraft Orion 27
Sailing Grounds: Southern California
Last edited by LittleWingCA; 08-21-2008 at 04:20 PM.