Parallax wrote:

In deep woods during a storm, I sat under a picnic shelter on top of a
dry picnic table on top of dry concrete. It jumped out of a nearby
conduit and to the DRY concrete floor in front of me.

Don't do that again - seriously. Here's the thing: Whether lightning strikes
something isn't related to the item's conductivity but to the amount of charge
it has built up. The arc will go between the highest charge in the cloud/air
and the highest opposite charge on the land. Wet or dry doesn't matter much.
You know this from rubbing a dry glass rod in dry wool or your dry feet across a
dry rug. It's worse the drier things are.

After the strike happens it is no longer a matter of charge, but power. The
amount of damage will depend upon whether there is a good path to earth. That's
where conductivity comes in. If there is no path the amount of 'surface effect'
increases, endangering people and things in the area.

Therefore it would be safer to stand next to a heavy copper flagpole embedded in
the earth than under a tree or in a 'dry' picnic shelter. Me, I'll stay here in
the Pacific NW and take my chances with tsunamis.

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?

No, careful and sensible. The only quarrel I'd have is with braided conductor
to your plate rather than a copper band. Harder to handle, but better capable
of handling the juice. As you live in Florida you might consider having your
plate attached to the hull - tightly with no intervening water - and permanent
connection to your shrouds. The 'air terminal' can be anything - a pointy rod,
those little brush things... etc. I am not familiar with a Faraday cage, but it
sounds knobby. For your purpose you want something sharp, which should have the
effect of allowing static charge to bleed harmlessly off. Then you want a heavy
bonding strap running the length of the boat. Anything important is bonded to
it, at right angles preferably, and the bonding strap is attached to the
underwater ground plate as well.

Essentially with this bypass ground, you are making your boat disappear from the
competition for the lightning.

If lightning does strike then your installation can carry off the charge, but
the whole idea is to avoid static buildup.

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?

Well, the minimum grounding plate is 1 foot square. Dyna Plates seem to be used
to ground single sideband transmitters. Stick with a copper plate. Two square
feet is overkill but does no harm and perhaps adds a comfort level.

Check into your local Power Squadron. Their educational offerings include
Marine Electronics which covers this subject, including the 'zone of protection'.

http://www.usps.org