On Mar 16, 12:52 pm, "Frogwatch" wrote:
On Mar 16, 9:58 am, dt wrote:



Don W wrote:

Roger Long wrote:

I'm not talking about doing it right here or protecting the boat. The
only aim is to increase the chances of remaining alive on a possibly
wrecked boat to deal with the aftermath. I'm just looking for a quick
stop gap to at least do something until I can put in a proper system.
It's tough on a boat with ballast encapsulated inside a fiberglass keel.

You've just figured out another important design criterion for a
sailboat--proper grounding for lightning protection. It needs to be
done as part of the design, instead of as an afterthought.

Regarding your aim of increasing your chances of remaining alive, I'm
not sure if you are talking about surviving the strike itself, or
possibly a sinking caused by the strike.

Don W.

Well, if he don't survive the strike, he probably won't survive the
sinking, either.

DT

A millisecond is a long time for lightning so the solder will probably
melt but will last long enough to conduct the pulse. The connection
is also crimped.
Many boats do get hit and survive and I'd go so far at to say that
most survive. You have to remember that at 10,000,000 volts, almost
everything looks like a conductor but some are better than others.
This means that a wet hull and deck look like perfectly good
conductors to the lightning. I have considered connecting the chain
plates together and then to the bolts at the mast step (deck stepped
mast) to try to make current that goes into the shrouds go back into
the grounded cable connected to the mast but this would make a huge
loop so am hesitant to do it.
I went so far as to use my dremel tool to round all edges on the chain
plates to suppress corona discharge from the edges.
You want to get that current to ground and do it with a large surface
area conductor which is why I use the many stranded wire. The
grounded plate has a lot of surface area too.
I think that the reason most struck boats survive is that the current
travels over the wet deck and hull surface which has huge surface
area. I have read that discharge pattersn are common on the outside
of struck boats , like Lichtenberg figures. My strategy is to
minimize this damage.


I believe that my battery cable will survive. Consider that lightning
rod cables survive multiple hits.

There is considerable disagreement over lightning protection
especially over whether you can prevent a strike by using pointy
conductors atop a structure. However, there is agreement on
protecting yourself when you are hit and that is to get the strike to
ground via a straight stranded cable.
I take an agnostic approach to the "pointy thing atop the mast
dissipating excess charge" and think that if it works that my Windex
will suffice.
BTW, if you have a carbon fiber mast and do not have a cable running
up the mast, you WILL lose the mast when struck. It has just enough
conductivity to conduct below the surface a bit and the heat in the
fibers destroys it.
A friend of mine in a 21' sailboat hit an overhead HT powerline. It
destroyed the mast leaving a very amazing melt pattern raining the
deck with molten Aluminum.
Another interesting thing is what happens to different trees that are
struck. Many trees survive being struck but not pines.

On Fri, 16 Mar 2007 22:22:25 +1100, Peter Hendra
wrote:

It is rather scary being the tallest
thing for miles of ocean when you see lightning ahead.

You bet. Lightning is fickle however. We were halfway to Bermuda
once, over 300 miles offshore when we got hit with a ferocious thunder
squall. The boat was a perfect target, all aluminum hull with an 85
ft mast. Lightning chose to hit a wavetop about 100 yards away
instead of us. We still lost all of the electronics except my pocket
GPS, just from induced currents. The pocket GPS was an early model
and hasn't worked in years now, but I still keep it around for
sentimental reasons. :-)

On Mar 15, 2:34 pm, "Roger Long" wrote:
Like the vast majority of fiberglass boat owners, I'm sailing around in a
boat with next to no lightning protection. I have run a heavy copper
grounding wire from a chain plate to a couple of through hulls directly
below. That will help bleed off some charge and slightly reduce the chance
of being struck. If I am hit however, I imagine it will make the results
worse.

This is on my "someday" list and would be on the "already done" list if I
sailed more to the south. I nearly 40 years of sailing in this part of the
world, I've only once been in a situation that I was huddled below trying to
figure out the best place to be when the bolt hit. That was long ago enough
that I haven't gotten as worked up about the issues as I should.

I don't know as much about the subject as I should since I've spent my
professional life working with boats that have metal masts welded on top of
metal superstructures welded to metal hulls. So, I throw out this idea for
comment as a suggestion for either an interim solution or for cruising
grounds where energetic storms are too infrequent to justify a major
retrofit.

How about a couple of plastic coated battery cables with a snap shackle on
one end and a length of chain on the other. If it looks like you are going
to get caught right in the path of an energetic storm, the kind where you'll
want to either anchor or drift while you seek the safest place in the boat,
just clip them to the shrouds and drop over the side. Nearly straight run
down from the stays (at least if chain plates are not too far inboard), lots
of surface area in the chain, plastic coated wire to protect the topsides.
You wouldn't want to cruise around with this rig but it seems like it might
at least keep a strike from sinking the boat by blowing a hole in it.

--

Roger Long

Most lightning protection systems are designed to ground your mast (or
lightning rod, on houses) to earth with a minimum resistance. The
theory is that by "equalizing" the potential of the mast with the sea
(or ground for houses) the lightning won't "see" the mast (or lighting
rod) as the lowest potential path to ground.

Sounds like black magic, and they always use heavy cables to ground
the lightning rods, so if you should get struck, it won't vaporize.
Sometimes the lightning strike has multiple paths to ground, so you
don't always get the full effect. Sometimes, you only get struck a
little bit (a near miss) so the total power through your ground path
is relatively small.

Nearly 60 years ago I started work with a shipping company, to train to
become an electrical engineer.

A few years later, after one of the companies ships had a topmast destroyed
by lightning (the topmasts were usually wood in those days as it was easier
to make a tapered spar this way and appearance still important), the company
decided that all the ships wooden topmasts should be protected by lightning
conductors, and in a shop where the youngest tech was in his 50s, I got the
job.



Every ship that arrived in Sydney had it's topmast inspected, and if not
conductored I would be assigned to go up the mast, measure up for a
conductor, make it, then up the mast again to fit it.

Unable to reach past the top of the mast in a bosuns chair I designed the
rod be the top part of the conductor fastened below the truck but projecting
above it. Usually the conductor consisted of a 1" x 1/4" copper strip, cut
at a 60 deg angle at the top (to give a sharp, lightning attracting, point),
joggled to go out around the truck and drilled every 2ft or so to be screwed
to the topmast, with a hole at the bottom to be bolted to the lower steel
section of mast.



One mast had a yard about 3' below the top and after being hauled as hi as
possible in the bosuns chair, curious because there appeared to be a
conductor already on the topmast, I climbed out of the chair by reaching up
and grasping the truck, stood on the yard and tied a rope around my waist
and the mast.

Hi and secure I was able to look down on the top of the truck and saw that
there had indeed been a lightning rod fitted previously consisting of a
piece of 1" rod that when screwed into a brass insert in the top of the
truck made contact with the conductor which went across the top of the spar,
beneath the truck.

Back in the workshop I rounded up a 12 in length of copper rod and machined
a thread to fit the brass plate with a nice sharp lightening attracting
point on the top end.



Back to the ship, hoisted to the top of the mast, I again grasped the truck,
climbed onto the yard and secured myself to the mast with a rope. I screwed
the new lighting rod into the truck and kept screwing so that the rod would
make firm contact with the conductor. I kept screwing and screwing waiting
for the connection to become firm, until finally the whole truck came away
in my hands and in shock I dropped it, fortunately not on my halyard
tenderers waiting some 60 ft below.



My blood ran cold. I had been using this truck as a hand-hold to hoist
myself out of the bosuns chair onto the yard. Yet the force of gravity on
its weight and a bead of paint around the junction with the topmast were all
that held it in place.



This was the closest I ever came to being killed by a bolt of lightning, a
bolt that occurred several months before, some thousands of miles away in
mid Pacific.



Remembered from the same period. A mate and I, just as we arrive in the
yacht club car park, were pounced on by a storm. We waited in the "Faraday
cage" safety of the car till the first fury had abated, then made a break
and dinghied out to the boat we were to spend the night on. Worried about
the boat being struck by lightning, which looked like coming back, we
connected a large shackle on a short piece of wire to the rig and threw it
into the water. Now "safe as houses", we turned in to be ready for our early
departure in the morning.

Of course the next morning we found that the piece of wire had been too
short and had the shackle suspended uselessly a foot above the water.



Another experience I remember. A mate who had a 26 ft keelboat on an inland
lake, new to sailing, was fascinated with the idea of sailing at night.
Knowing that I had done a god bit of night racing asked me if I would
organise a night sail for him.

I picked out a full moon night (the lake was formed by a dam and there were
plenty of trees growing out of the water), got hold of another couple of
experienced mates and off we set.

We'd gone about 6 miles across the dam when a storm obscured the sky, and
lightning flashed. We turned back, stationing one hand in the pulpit too
keep a look out for trees, fingers crossed. The wind piped up as it does
with a storm and we were soon having an exciting sail, rail down, in the
dark, when one of the crew (a mechanical engineer) noticed that there were
sparks cracking between the boom and the mast. Fascinated by this he tried
to interest the man in the pulpit (a mining engineer) who "did not want to
know anything about it", while the man on the tiller (electrical engineer)
made sure he kept well away from the lifelines and other metal. The owner,
an intrepid soul, wide eyed with the excitement of it all, and thoroughly
enjoying his night sail. We made it back to the mooring without damage.



Another example. Some 5 years ago an almost septuagenarian couple were
caught in, their now power cruiser, in a storm while researching the island
we now live on. We had anchored in a spot where we were sure there was a
good bottom and sat on the bridge to watch the storm. We had wind and rain
and lightning, as you do, and I remember suggesting to my wife that maybe I
should get some soap and clean the outside of the clears relying on the rain
to rinse them. She demurred, on the grounds that it would be too dangerous,
after all we were protected from the lightening by our cloth bimini top and
clears, so I waited till the first squall passed and then washed the outside
of the clears and the next (worse) lot of rain wind and lightening rinsed
them clean. It was a bit like when you were a kid, in bed, and worried about
monsters, you pulled the blanket over for protection. It worked for me; none
of the monsters got me.



How about carrying a blanket. Maybe even a Teddy as well.



To be serious, I do not believe that there is a definitive answer to the
task of protecting a yacht from lightening unless it's made of steel.



In Australia anyway, the main thing is to not play golf, as this is where
the statistics say you are most likely to be killed by lightening, even
worse than shark attack.

On Sat, 17 Mar 2007 06:17:03 GMT, "barry lawson"
wrote:

In Australia anyway, the main thing is to not play golf, as this is where
the statistics say you are most likely to be killed by lightening, even
worse than shark attack.

Same thing here in south Florida. We usually have several fatal golf
course incidents every year.

So golfing is bad, good thing since my game is terrible anyway.

Regarding the boat, a well grounded mast, shrouds and stays seems to
be the consensus and jibes with my experience. If caught out, staying
away from metalic objects as much as possible seems prudent. That
said, I had a friend who was on a fully crewed 35 footer that was
struck twice in one weekend. All of the electronics were toast but no
one was injured at all, and there was no damage to the hull.

Every once in a while you hear about someone with a plastic thru hull
transducer getting blown out by lightning.

Wayne.B wrote:
I had a friend who was on a fully crewed 35 footer that was
struck twice in one weekend. All of the electronics were toast but no
one was injured at all, and there was no damage to the hull.

Do you know how it was equipped (or not) for lightening protection?

Rick

On Mar 17, 10:42 am, wrote:
Wayne.B wrote:
I had a friend who was on a fully crewed 35 footer that was
struck twice in one weekend. All of the electronics were toast but no
one was injured at all, and there was no damage to the hull.

Do you know how it was equipped (or not) for lightening protection?

Rick

Golf is Florida Nature's way to get rid of excess tourists.

On Sat, 17 Mar 2007 09:42:45 -0500, lid wrote:

Do you know how it was equipped (or not) for lightening protection?

=============================

Don't know.

"Roger Long" wrote...
Like the vast majority of fiberglass boat owners, I'm sailing around in a
boat with next to no lightning protection....

Related question -

I am building an open 20' power boat, of all-aluminum construction. It will
be used in all weather conditions, sometimes for "time-critical" trips. I
have toyed with the idea of shipping a short mast (boathook?) to disperse
any electrical charge, and hopefully channel any direct strikes along a
known path.

Any thoughts?
Sal's Dad

"Sal's Dad" wrote in message
...
"Roger Long" wrote...
Like the vast majority of fiberglass boat owners, I'm sailing around
in a boat with next to no lightning protection....

Related question -

I am building an open 20' power boat, of all-aluminum construction.
It will be used in all weather conditions, sometimes for
"time-critical" trips. I have toyed with the idea of shipping a short
mast (boathook?) to disperse any electrical charge, and hopefully
channel any direct strikes along a known path.

Any thoughts?
Sal's Dad

Yes, it's a dumb idea. What you have there is a Faraday cage. If you get
caught in a lightning storm sit or lie down in the center of the boat so
your head is below the gunnels and you will be protected by the Faraday
cage. Erecting a mast will only attract a lightning strike.

http://en.wikipedia.org/wiki/Faraday_cage

Wilbur Hubbard