After I added an aluminum radar arch, I felt a bit more vulnerable to
lightning strikes. I think I added a simple, inexpensive measure of
protection. Here it is:

I bought a pointed aluminum spike (West Marine, I think) with base and added
a three foot threaded rod all of which is bolted to the top of the arch.
(It's supposed to dissipate static buildup. Another type is like a bristle
brush pointing skyward.)

I drilled a 3/8" hole in  one base leg and added a bolt and nut plus a
wingnut. A 12 foot length of #4 battery cable was fitted soldered with
connectors at each end and a big zinc fastened to one end.
When bad lightning approaches, I just fasten the wire to the wing nut and
drop the big zinc overboard. This can be left in place while at anchor or
dockside.

I chose this, admittedly not perfect solution, because I did not want to lead
possible  lightning anywhere inside my boat.

Rob Brueckner

I really don't have time to reply to this, but I think this advise is
dangerous, albeit good intentioned.

Rob Brueckner wrote, "I bought a pointed aluminum spike (West Marine, I
think) with base and added a three foot threaded rod all of which is
bolted to the top of the arch. (It's supposed to dissipate static
buildup. Another type is like a bristle brush pointing skyward.)"

Dr. Ewen M. Thomson is the most knowledgeable authority that I know of.
He has an excellent web site at
http://www.thomson.ece.ufl.edu/lightning/ His section on air terminals
at http://www.thomson.ece.ufl.edu/lightning/AirTerminals.html reads, "
Sharp or blunt?  Almost every lightning air terminal you are likely to
see has a sharp point.  The theory behind this was that a sharp point
causes the largest electric field and hence is more likely to launch the
attachment spark.  However, recent research indicates that blunt rods
are more effective in this task..."

Rob Brueckner wrote, "I drilled a 3/8" hole in  one base leg and added a
bolt and nut plus a wingnut. A 12 foot length of #4 battery cable was
fitted soldered with connectors at each end and a big zinc fastened to
one end. When bad lightning approaches, I just fasten the wire to the
wing nut and drop the big zinc overboard. This can be left in place
while at anchor or dockside."

In Dr. Ewen M. Thomson's presentation at Melbourne Trawlerfest, he
indicated that the charger front of a thunderhead extends many miles
ahead of the thunder cloud itself and that by the time that most people
realize that they are in danged of a lightening strike, the risks are
already quite high. The worst thing you can do at this point is connect
a "protection" system.

Dr. Ewen M. Thomson also pointed out the case studies show of lightening
strikes reveal that the conventional wisdom of connecting your
lightening ground to the keel isn't adequate or even beneficial.
Lightening is attracted to the surface charge and ground should be at
the waterline.

The best protection from lightening strikes is a metal hull. I don't
understand why metal hull boats aren't more popular in the high
lightening frequency areas.

Regards;
Mike Schooley
Designing "Portager" a 36' trailerable trawler
www.portager.info

In an earlier life, as an electrical engineer for an electric utility, I
used to oversee lightening protection design for our facilities. Back then,
there was a common rule of thumb: A lightening rod will protect a 30 degree
cone around it. Two adjacent rods will protect a 60 deg angle between them,
and 30 deg on the outside.

I get a real kick out of sone of these two foot lightening rods on barns.
They are only protecting a couple feet of the barn.

There are now more sophisticated techniques based on a sphere rolling above
the protrusions being protected, but that discussion would be over sharing!

Lightening protection is very much an art.

Ted Grave
GB32, AMICI
Branford, CT