Jere Lull wrote in message ...
In article ,
(Parallax) wrote:
We often see some discussions about lightning protection but here in
FL, it is really a major problem snip
My normal lightning protection
method is to try to get it to ground as quickly as possible. I have a
2'X2' copper sheet with a very large tinned copper braid soldered and
crimped to it that I drop overboard. The otehr end of the braid has
two welding clips that I attach to the upper and lower shrouds near
the deck. I turn off and unplug all electronics and stay away from
all metal fittings. I have even considered a retractable Faraday cage
attached to the mast head consisting of small wires to protect the
boat inside it. Am I too paranoid?
Having lived in Clearwater for 5 years, I'd say "NO!" to being paranoid.
Sometimes they ARE out to get you.
My 28' S2 has internal ballast, otherwise I'd use the keel as ground.
Being VERY familiar with high voltage discharges, I use braid because
such discharges have high frequency components so they need a lot of
surface area to carry the current. I considered fastening the copper
directly to the hull with the braid fastened from inside but
considered:
10,000 amps X10,000,000 volts = 10E10 watts dissipatted in about 50
nanoseconds,sorta like hitting your hull with a big sledgehammer.
Thunderstorms in Clearwater may be even worse.
In that area of FL, I'd probably have leads hanging from all 4
"corners", permanently attached with bulldog clamps, not dinky welding
clips ;-) They would be clipped to something while under way. I figure
about 6' of copper strand in the water is sufficient and plates are
bulky, so would use zinc guppies to weigh them down so they could "live"
in the water while we were away from the boat.
However, I am curious about lightning protection for less afflicted
ppl. I have seen these ground plates consisting of sintered bronze
powder that are fairly small but have high surface area due to the
many sintered particles (Dyna-Plate). I can believe these may work
for low E fields and low current but I do not believe they work for
high fields and high currents (like lightning). I think the small
passages act like tiny Faraday cups allowing no field inside and the
effective surface area is not much larger than the external area.
What do others think?
That sounds sorta reasonable to me. Our iron keel is our ground, so I
haven't worried about it much. I believe most people hope that making
the mast "look" like ground with a good Dyna-Plate or similar will
protect them.
Personally, I think that making a Faraday cage out of the shrouds is the
best bet, but there are no guarantees. Friends put one of those bottle
brushes up on the mast -- factory approved tech did it -- and they got
struck a week or so later.