more on lightning

james nolan (
Thu, 5 Aug 1999 07:46:22 -0600

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West Wight Potter Website at URL
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When the sparks are flying and your hair is standing, one may get the urge
to ground the mast. It should be noted that this "ground" isn't ground at
all, it is a highly charged source of ions. The large cloud of charge above
induces opposite charge in the ground or water. By connecting the mast to
the "ground" you are allowing a flow of ions off of the mast. This flow
reduces the ion density in your local area, hence lowering the potential in
your area. The speed at which these ions move is proportional the charge
density divided by the conductivity of the ground. The charges move slower
in fresh water than salt. The principle behind lightning rods and mast
grounding is to reduce the local ion density to reduce the chance of a
If lightning does strike the mast it can come from the sky down or from the
mast up. The ground path is very important here because it directs the
initial conduction current before the strike and sets up the current path in
the plasma of the ionized air surrounding the lightning strike. The plasma
can linger for seconds after the strike and is sometimes seen as a glow or
white fire. Since the lightning has high potential and high currents it can
induce voltages and currents in surrounding objects. Also the lightning is
an impulse so it contains a broadband of frequencies.
Lightning currents can blow out radios and electronic equipment without a
direct hit. It can also stop a human heart from beating without a direct
hit. 10 mA can induce cardiac fibrillation. The ground currents after it
strikes can also electrocute. What I do for lightning is hang a chain off
the forestay into the water. I wonder about grounding the mast because it is
in the center of a Faraday cage formed by the shrouds. I think it might be
better to "ground" all of the shrouds than just the mast. This would keep
currents on the outside of the boat. Maybe you can run wires from the shroud
anchors inside of the boat to the keel. You could contact the keel with a
set of large brushes. Also passing large currents through the iron keel
would magnetize it, perhaps very strongly. I also would not like my head
next to a cable carrying a million amps, you may wind up like Randall P.
Lightning is also a concern of alpinists and there was an outfit in England
that sold a conductive rain poncho to shunt ground currents. This would
suggest that covering yourself with tinfoil would shunt induced currents and
reduce the induced currents in the body. If you were directly hit wearing
tinfoil, the tinfoil would keep the grease from splattering and there would
be no messy cleanup. I would use Reynolds foil and expect a royalty for
this. I think a wetsuit would be better to reduce shocks from induced
currents in other objects. However the wetsuits do not reduce the currents
induced in you. Maybe painting the inside cabin with conductive paint can
form a safe Faraday cage. Another possibility is to spray a water mist
around the boat. The water droplets would pick up the local charge and be
pulled skyward by the charge above. If the water nozzle is carefully chosen
you can get a very fine mist. This fine mist combined with an atmospheric
electrometer would allow you to determine the charge to mass ratio of an
electron, just like Robert Millikan did many years ago, but without the
environmental impact of having to use oil. This experiment can handily
divert the crews mental state from fear of lightning strikes to the joyous
anticipation of scientific discovery. Also scientific apparatus displays
nicely at the yacht club.

Jim Nolan