Re: Lightning & Boats
Bob Amick (amick@spot.colorado.edu)
Fri Jun 26 23:02:03 1998
Martin,
I can't comment on the devices intended for marine installations,
but the ones that are designed to protect radio antenna towers
do seem to work very well. They are shaped like an umbrella and
the theory is that the larger surface area presented by the array
tends to dissipate the charge potential more quickly thus lessening
the probability of a direct and destructive strike to antennae and
adjacent structures.
This is one of the reasons that traditional lightning rods are now
thought to be hazardous. They tend to be shaped like needles and
thus concentrate the corona into a very small area increasing the
potential for a destructive lightning strike.
Sarasota Florida is one of the highest strike zones in the country
and many of their radio towers are protected by the umbrella-type
dissipators. I think that one of the vendors for this type of
technology is Lightning Elimination Associates (LEA) and they
may have a website. Some of their literature indicates that
the annual damage to radio towers and antennae/cabling has been
substantially reduced by the arrays. Antennae should be mounted
below the dissipator arrays if possible.
To protect your radios, it is a good idea to use Polyphaser gas tube
surge protectors that are well grounded on the antenna cables.
These are available from most commercial two-way radio dealers and
run about $40-$50 each. But they may save a far more expensive radio.
Similarly, electrical devices should be protected by metal oxide
varistor (MOV) surge protectors in series with the power input
to any electronic device.
Another important factor is to bond/ground all electrical devices
to the same ground circuit. This keeps any surge/lightning voltage
potential uniform and thus is less likely to result in arcing and
damage to sensitive semiconductors and chips in the event of a strike.
I have heard that the preferred way to protect a non-metal mast is
to fit it with large braided lightning ground cable linking
the lightning-dissipator array to a large metal plate directly
below the mast on the bottom of the vessel. Perhaps others more
knowledgeable could shed some light on this topic.
Best wishes,
Bob Amick, Explorer Advisor, High Adventure Explorer Post 72/SES 72
Boulder, CO
At 07:37 PM 6/26/98 CDT, you wrote:
>Our boat SEAHORSE, was apparently the victim of a direct lightning strike
>this week. Both the primary VHF & SSB whips (both 22' long & mil-spec) were
>reduced to very small fiberglass strands with exploded metal fittings.
>
>The question that I have is: Do those "corona-discharge" gadgets seen in
>the marine stores do any good? To my knowledge, none of our boats have
>been struck before.
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