Larry Demers wrote:

Jim,

I can get a #1 cable from the mast receptacle on the deck (deck stepped), down
to the encapsulated keel with a couple small gentle curves. Tapping into the
keel with a fair sized threaded rod will be interesting I suppose. Any hints?
I have a Cape Dory 30.

An encapsulated keel has no connection to the sea. Did you want the
lightning to chew a hole to get out of the keel?

Better to stick a sheet of copper onto the bottom (outside) with
epoxy and lead a heavy wire to it, possibly through a fat bolt above
the waterline. Keeping the wire to it straight seems important, but
bend size is relative. A small deviation from straight won't matter
near as much as a sharp deviation.


Any consideration to the idea that the conductor that the lightning streamer
takes upwards at the start of the stroke, will be vaporized by the streamer,
forming a very low resistance plasma pathway for the main downward stroke to
follow. This would seem to throw away the inductive effects of the conductor
for the main charge. The leader though, would feel that inductance I suppose,
which would effect how high the stepped leader goes and how far downward the
main charge has to reach for a completed path.

Inductance is cumulative, like resistance, any component in series
will increase the inductance, but in and of itself, straight wire
inductance isn't a problem unless it is mutually coupled to another
component, even one so esoteric as another section of the main
conductor dispaced at some relative parameter so as to cause a balun
effect of sorts, which might induce a flashover if an alternate path
is nearby, or if the coupling effect causes the formation of a
plasma leader from the bend, relaunching the main bolt exploratory
process we are familiar with in the initial strike process.

Electricity has no momentum, so it can stutter along until a good
short circuit is established. The frequencies involved would seem to
include a calculation of the distance, any resonances excited, and c.


Inductance in the boats ground path (too small a conductor)

Sorry, but this would be resistance.

would seem to
cause side flashes to surrounding metallic objects on the boat that have a lower
resistance (impedance really?),

Inductive reactance. The resistance doesn't matter, really, except
to determine the distribution of points at which work will be done
by the passage of current.

See my other post in this thread relative resistance.


and then to a local ground. It can get into the
laminate and do real damage that way.

Cheers,

Larry DeMers

Jim Donohue wrote:


Lightning does what it wants..not what you want. The mast is a much larger
and somewhat shorter conductor than anything you could run along the
shrouds. So the stroke will divide and almost all of it will stick with the
mast. When the stroke reaches the bottom of the mast some of the energy
will return to the shroud ground via whatever path...destroying anything in
the way.

Including the surface of the mast itself, hopefully. Other
components are more likely to fail if called upon to conduct too
heavily. A thousand amps will easily fuse a shroud, while it might
only chew up an aluminium mast.


Straight to the water is best. If not then very gentle and heavy curve to
water. Shortest is best...if not shortest than as close as practical. All
deviations from straight and shortest increase the probability of damage.

Jim Donohue

"Courtney Thomas" wrote in message
...

What would be wrong with a long, ....straight.... piece of aluminum rod
in contact with a location as desired/convenient near the mast top,
(running alongside a shroud) into the water ?

Courtney




Parallax wrote:


Thunderstorms every day and my fear of lightning (totally justified)
have caused me to once again scheme up a way to protect my sailboat.
For protection while anchored, I have a 2'X2' copper sheet with very
thick stranded tinned cable with a clamp for attachment to the mast.
I have considered using this while underway but it would cause too
much drag and would probably foul the prop.

So........another useless idea. How could you tow a lightning ground?
Such a ground doesnt have to be a sheet. it just has to have large
surface area. Could attach it to the bottom of the dinghy and tow it
with proper cable going to the mast but I try not to tow my dinghy.
OK, why not something like a boogie board (foam) covered with Cu foil.
No matter which side it had in the water, it would have lots of area
submerged. It would produce minimal drag. Any thoughts?



--
s/v Mutiny
Rhodes Bounty II
lying Oriental, NC
WDB5619




How about a sheet of copper towed by a solid piece of angle iron
hooked onto the backstay, kinda like a copper covered steering oar
(maybe even your emergency steering paddle?) I admit, I am partial
to double duty thingies, actually known as monkeys aboard ship.

If the backstay gets vaporised, the sail, mainsheet, topping lift
and lower shrouds will likely still support the mast, so long as you
are not sailing hard. A spare halyard can sister the blown backstay
to get you home.

It is the highest resistance component in the path that will take
the brunt, protecting other more conductive elements. Perhaps a
purposeful higher resistive part in the discharge path, kina like an
anti-fuse? Even a piece of chain? Once a discharge path is
established, the charge will start to heat it up. Metallic objects
may vaporise, starting a metal vapour arc between links.

I know nothing of the behavoir of chain in a lightning discharge, it
never came up. I can think that it may work fine, presenting a
re-useable damage limiting sacraficial element, with a considerable
service lifespan. It may well get welded into a straight piece of
knobby artwork still useful as a rural mailbox pillar.

Terry K