Any thoughts?

How about a steel hulled and decked boat? Mine has a deck-stepped
mast (actually two) with a steel compression post under them. Is the
lightening likely to hit the steel deck and go around the outside like
a Faraday's (sp?) cage, or is it more likely to make the jump to the
compression post and keep going straight to the steel keel?

Lee Huddleston
s/v Truelove

Lee Huddleston wrote:
Any thoughts?


How about a steel hulled and decked boat? Mine has a deck-stepped
mast (actually two) with a steel compression post under them. Is the
lightening likely to hit the steel deck and go around the outside like
a Faraday's (sp?) cage, or is it more likely to make the jump to the
compression post and keep going straight to the steel keel?

Lee Huddleston
s/v Truelove

If all the bits are well connected (ie. no salty rust layers
between parts , etc.) I would expect the lighning to go via the
shortest path, given a choise of paths with similar geometry. Is
there a rubber pad or something under the mast heel?

This means I would expect your king posts(s) to sink most of the
bolt's current.

Something I realised isn't thought much by many is that all that
power has to be dissipated, or absorbed between the cloud and the
earth. That means that somewhere, the place with the biggest
resitivity, will get zorched while the other parts of the discharge
path may carry mucho current but will not dissapate the major whack
like what would happen at the point where a rusty old bolt is
expected to complete the circuit. That old bolt between the
overhead and the king post, or between the king post and the keel
could become the focus for a billion watts or so. That bolt might
vaporise, forming a metallic vapor arc lamp for a split second
while the rest of the path remains relatively unaffected. It is all
a question, like so many others, of relative resistivity.

If the path struck is pretty well connected, with no salient
resistance point, the surfaces in contact with bolt and earth will
bear the brunt. A large low resistivity contact area with the sea
will mean that the point where the bolt strikes, usually the mast,
will take a kicking. My mast had 25 half inch holes burned in it,
all along the port side upper foreward half, while there was little
else to show for damage except at the point where the keel bolt
passed through the hull, which aquired a slow drip leak.

I believe this was because the aluminium oxide coating the mast,
being a relatively poor conductor, is the point at which the most
resistance was developed in the current path, boiling the mast
material at that point and caused each mini stroke to extinguish
completely and requiring the next mini stroke to re-establish an arc
somewhere else on the mast with the same (near minimum) surface
curvature. It narrowly avoided the upper(ungrounded at the deck)
shroud. The holes were spaced about 6 inches apart. It is a textbook
example, I would expect, of typical and classic lightning behavoir,
consistant within it's parameters, not a freak. It repeated this
behavoir 24 more times. Perhaps the keel bolt got hot enough to
swell, squashing the bedding material, at the least.

Insurance replaced the mast. There was no other damage, surprising,
really, because the mast was in the return path for the spreader
light, using the VHF antenna coax ground. The spreader light was
wired this way when I got the boat, and frankly, given my
experiences, I am loathe to wire it "properly." The lightning ground
is a 3-0 wire from tabernacle to a keel, using the 4 mounting bolts
for the tabernacle passing through the now epoxy, then cored
fiberglass overhead, connected to an aluminium backing plate at the
top of the wooden king post. Some of the balsa there was rotton.

I believe I watched the top end of the bolt as I sat on my back
porch watching the storm from 10 miles away. The bolt appeared to
be quite heavy and of long duration, but that impression may be only
a result of the dynamics involved in the discharge, ie. 25 seperate
strokes, spread out a little in time, seemingly longer in duration
and enhancing my perception. I had no suspicion at the time that my
boat had been struck and it wasn't until a week later that I noticed
marks on the topmast.

It was, or seemed, by far the strongest bolt in that storm.

People inside your steel hull and cabin would be well protected as
long as all the connections between parts inside do not contain
relatively high resistance connections, though, being relative, one
point will always be "the highest" resistance and no matter how
low, that is where the sparks will fly as they did on my mast, where
the aluminium oxide presented the point to develop most of the power
dissipated above the sea, discounting the lightning bolt's display
itself.

Terry K

Easiest is a set of battery jumper cables cliipped tothe shrouds with a
round turn andthen drag them in the water. One for each side. I don't
remember the exact physics but it creates a cone of safety effect and
wonder if anyone else remembers and can address that particular point.

"Larry Demers" wrote in message
...
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.

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 in the boats ground path (too small a conductor) would seem
to
cause side flashes to surrounding metallic objects on the boat that have a
lower
resistance (impedance really?), 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.

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

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.

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 in the boats ground path (too small a conductor) would seem to
cause side flashes to surrounding metallic objects on the boat that have a lower
resistance (impedance really?), 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.

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

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