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Ocean Sailing and Boating by Albert                                                             mail to Albert

News from the Oceans,                                                                                                        

Send me your comments, experiences, emotions we give them  to all our friends.

October 1999

Can Lightning Strikes Be Prevented?

Last year as my new boat was sitting on dry storage just prior to
commissioning, she was struck by lightning. The results were pretty
horrendous:the strike destroyed the autopilot, the depth finder, the
wind instrument and the log/knotmeter,melted the stainless steel VHF
antenna and the coaxial cable inside the mast, wrecked the control panel
of the refrigerator and the battery charger, and burned all navigation
and cabin lights.Fortunately, nobody was aboard when lightning struck
and the manufacturer's insurance covered all costs (the boat title had
not yet been transferred to me).Needless to say, I have since become
keenly interested in lightning and whatever technology is available to
reduce its risks or minimize its consequences.Unfortunately, the
impression that I have formed is that , whereas we seem to have learned
quite a bit about lightning, the technology to deal with it has not
progressed much since the time when Benjamin Franklin was flying his
kites in a thunderstorm.
Of course, anybody who has read something about boating knows that in
a fiberglass boat with an aluminum mast, the mast itself is likely to
function as a lightning rod. To reduce the risks of damage to the boat
or her occupants, the mast, the stays and the shrouds should be "bonded"
with heavy gauge copper wire to the sea cocks, the propeller, the ground
plate (if you have one) - anything that touches the water. This creates
a "Faraday's cage" that is supposed to carry any lightning strike to
ground.The result should be a "cone of protection" centered on the tip
of the mast and with a radius approximately equal to the height of the
mast.So if you are caught in a thunderstorm, stay away from the mast,
don't touch anything metallic connected to it, and pray that the above
theory is correct.
So far so good. But is there anything that we can do to prevent
lightning from striking? There are at least two manufacturers I know of
(Forespar and Lightning Prevention Systems,Inc.) who are offering
"lightning prevention systems" based on the idea of dissipating the
static charges that tend to form on your boat during thunderstorms. The
theory goes, more or less, as follows. All lightning strikes from clouds
to ground start near the base of the cloud as downward discharges about
50 m long, called "stepped leaders". When stepped leaders get near to
the ground, streams of electrons ("streamers") move up from certain
objects on the ground such as buildings, trees, towers and, yes, boat
masts. When a stepped leader meets a streamer, a ionized channel is
created which becomes the path for the lightning strike. The (positively
charged) cloud is thus short-circuited to the (negatively charged)
ground and a current of a zillion amperes rushes toward your electronic
gear and anything else (possibly uninsured) that it can destroy in the process.
Since there is nothing you can do about stepped leaders, the question
is whether you can at least prevent the formation of streamers,e.g. by
reducing the building up of static charges on your boat during a
thunderstorm.The solution that Forespar and LPS think they have found is
to install on the top of your mast what they call "dissipaters"-
basically, a bunch of stainless steel wires tied together as a bouquet
or a brush, that should dissipate wandering electrons in all directions
thus preventing the formation of a single path to the cloud.
The question is: do they work? Frankly, I don't know and I don't think
anybody does.But it seems an intriguing idea- better in any case than
flying kites in a thunderstorm. Does any of our readers have any
experience in this area? Let's discuss and , in the interim, avoid
thunderstorms if you can.

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