Re: Lightning & Boats
Amick Robert (amick@spot.colorado.edu)
Sat Jun 27 21:51:15 1998
Martin, et al
Sounds like you have state of the art protection in place already.
I neglected to mention that my experience with fiberglass communications
antennas and lightning has been generally worse than solid aluminum
versions. We have had several direct hits over the years on antenna
structures; the aluminum antennas did not sustain significant damage,
however the fiberglass models were invariably exploded or severely
damaged..
I would guess that the high conductivity of your mast handled the
dissipation of the energy effectively without damage. Lightning bolts
are five times hotter than the surface of the sun, but if they contact a
highly conductive surface with a good path to ground, will usually cause
far less damage than if the surface has substantial dielectric resistance
or a circuitous path to ground.
If you have the option of installing an aluminum antenna
versus a fiberglass model, I would recommend the aluminum model.
Depending on the frequency range, you can usually get either an aluminum
or a fiberglass version. Our radio technicians have indicated that the
aluminum generally conducts the strike far more efficiently to ground,
thus sustaining less damage if any to the antenna dipoles. Most aluminum
antennas are designed to provide direct current shorting to ground, but
conduct r.f. energy very efficiently. Fiberglass covered wire-wound/loaded coil
antennas cannot provide this dc conductivity nearly as well, so tend to
suffer the consequences.
Bob Amick, Explorer Advisor, High Adventure Explorer Post 72/SES 72,
Boulder, CO
On Sat, 27 Jun 1998, Martin A. Flynn wrote:
> At 11:07 PM 6/26/98 CDT, you wrote:
> Bob,
> SEAHORSE is 65' LOA, aluminum hulled. The mast is 3" aluminum pipe
> tripod which was roughly parallel to the affected antennas. I could find no
> burn or scorch marks anywhere on the superstructure exterior, so from what I
> can tell the antennas took the brunt of the strike.
> The coax from all the antennas are protected by polyphasor bulkhead mount
> arrestors already. The problem apparently was the antennas themselves
> could not carry the current & were destroyed.
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