Larry wrote:

http://www.thomson.ece.ufl.edu/lightning/

This sailor has done extensive research at ufl.....

Thanks, that was one of the first things I turned up. This quote is
especially applicable to this thread in view of Wilbur's comment that an
ungrounded boat is less likely to be struck:

"While the individual estimates varied widely between surveyors, there is no
support for the argument presented by some sailors that they should not
ground 'their sailboat since it will increase the chances of it being
struck by lightning."

The statistics presented in this article make a good case for just
forgetting about it unless I plan to sail south, which I do hope to do at
some point.

My original post was actually prompted by this and a couple of other web
articles. Here is my situation:

http://home.maine.rr.com/rlma/Keel.jpg

The mast stanchion is essentially equal to a keel stepped mast. Since my
boat was originally a keel / centerboarder, the keel is large volume and I
doubt that Endeavour spent the money for a keel casting. I'm quite sure the
ballast is just stacked lead pigs in resin. Lighting current going through
that stuff would be like a bomb and the high resistance at the bottom of the
main conductor would create extensive side flashing.

For reasons not evident on the crude drawing, any grounding plates have to
be outboard of the cabin sole. The Thomson paper says not to let grounding
conductors contact the hull but I have no choice if I am to maintain the
maximum radius recommended by other sources. The reason for overkill on
conductor and ground plate size is to compensate for the tight conductor
radius and need to run the conductors close to the hull skin.

--
Roger Long




















--
Roger Long

Roger Long wrote:
Larry wrote:

http://www.thomson.ece.ufl.edu/lightning/

This sailor has done extensive research at ufl.....


Thanks, that was one of the first things I turned up. This quote is
especially applicable to this thread in view of Wilbur's comment that
an ungrounded boat is less likely to be struck:

"While the individual estimates varied widely between surveyors,
there is no support for the argument presented by some sailors that
they should not ground 'their sailboat since it will increase the
chances of it being struck by lightning."

The statistics presented in this article make a good case for just
forgetting about it unless I plan to sail south, which I do hope to
do at some point.

My original post was actually prompted by this and a couple of other
web articles. Here is my situation:

http://home.maine.rr.com/rlma/Keel.jpg

The mast stanchion is essentially equal to a keel stepped mast.
Since my boat was originally a keel / centerboarder, the keel is
large volume and I doubt that Endeavour spent the money for a keel
casting. I'm quite sure the ballast is just stacked lead pigs in
resin. Lighting current going through that stuff would be like a
bomb and the high resistance at the bottom of the main conductor
would create extensive side flashing.

For reasons not evident on the crude drawing, any grounding plates
have to be outboard of the cabin sole. The Thomson paper says not to
let grounding conductors contact the hull but I have no choice if I
am to maintain the maximum radius recommended by other sources. The
reason for overkill on conductor and ground plate size is to
compensate for the tight conductor radius and need to run the
conductors close to the hull skin.

-- Roger Long
The problem is, lightning doesn't like going round corners and *will*
jump back out of the lightning conductor at the bend.

E.M. Thompson states:
At this time the peak lightning current is generated, during the
'return stroke'. Although cresting at ten thousand to hundreds of
thousands of amps, it only lasts for about a millionth of a second.

This 1 us pulse considered in the frequancy domain has a fundamental at
1 MHz and various unspecified (we dont really know the pulse shape)
strong harmonics going *way* up. As a mimimum, the grounding system
*MUST* have a low impedance from DC to 10 MHz which essentially
prohibits anything except large radius bends through less than 90
degrees. Due to the 10 KA current pulse, an extremely high voltage
will be developed accross any bend, so there is an extreme risk of
arcing to the hull if the bent strap is in the bilge. If its touching
the hull, you basically needn't have bothered fitting it from the point
it touches the hull onwards to the grounding plate.

The other nice little problem is that multiple KA currents *will*
straighten out any sharp bends in the conductor carrying them and a
lightning strike consists of multiple strokes so the grounding system
has to survive in usable condition to be effective.

The main lightning conductors need to be joined to the mast support post
at least as high above the grounding plates as the lateral distance
and led in a smoothly swept curve. Unless your pillar is very close to a
bulkhead this may not be practically achivable.

Once you've led the lightning below decks, you are basically screwed
unless you can lead it almost streight down and out. Once you've led it
below the waterline you are totally ****ed unless you can get it out to
large area grounding plates.

From your description, I dont see how anything except boring the top of
the keel downwards and outwards for thick pure copper conducters to
ground plates extending from the sides of the keel to the turn of the
bilge could help much. There are problems with this approach as well,
as the conducters will try to move quite a bit duing the strike and if
undersised and they go open circuit during the strike could cause major
explosive damage to your keel root.

Sounds like I'd better stay north of Cape Cod

I've thought of drilling the keel since lead is fairly easy to drill. I'd
want to be sure there wasn't any scrap iron in the ballast mix though.

How thick a copper conductor do you think would be safe? The mast support
is only about 1 1/2" stainless steel pipe so it would be reasonable to
exceed it's cross section area and current carrying capacity. OTOH if the
mast support itself is insufficient, maybe I should just forget the whole
thing and put my faith in prayer.

I ran a copper wire of the kind used to ground electrical meters from one of
the shroud chainplates to an unused through hull in a fairly gentle sweep
when I first got the boat just to have something to lead a strike a way from
people inside. I still expect a major strike would sink the boat but
thought it might increase the chances of being alive to get into the dinghy.
Now I'm thinking I might be better off without this connection. What do you
think?

What would be the probable effectiveness of a portable system? Say, four 1
sq foot copper plates attached to 4 GA wires shackled to headstay, backstay,
and shrouds before anchoring or drifting for a major electrical storm?

--
Roger Long

On Nov 9, 8:24*am, "Roger Long" wrote:
Sounds like I'd better stay north of Cape Cod

I've thought of drilling the keel since lead is fairly easy to drill. *I'd
want to be sure there wasn't any scrap iron in the ballast mix though.

How thick a copper conductor do you think would be safe? *The mast support
is only about 1 1/2" stainless steel pipe so it would be reasonable to
exceed it's cross section area and current carrying capacity. *OTOH if the
mast support itself is insufficient, maybe I should just forget the whole
thing and put my faith in prayer.

I ran a copper wire of the kind used to ground electrical meters from one of
the shroud chainplates to an unused through hull in a fairly gentle sweep
when I first got the boat just to have something to lead a strike a way from
people inside. *I still expect a major strike would sink the boat but
thought it might increase the chances of being alive to get into the dinghy.
Now I'm thinking I might be better off without this connection. *What do you
think?

What would be the probable effectiveness of a portable system? *Say, four 1
sq foot copper plates attached to 4 GA wires shackled to headstay, backstay,
and shrouds before anchoring or drifting for a major electrical storm?

--
Roger Long

4 gauge may be a bit small. A fellow in my old marina took a scrap
welders lead and cut 6 ft sections and had them saddled clamped to the
shrouds on each side, had them coiled and zip tied to each side. In a
storm he just cut them loose and figured that would be the least path
of resistance right down into the water.

As Neal's example proved when the lighting jumped in an air arch to
his skull lightning seeks the path of least resistance.

I dont think he's been struck yet to test his system. He has many
taller boats all around him.

Joe

"Roger Long" wrote in news:gf6rq3$mk0$1
@registered.motzarella.org:

Sounds like I'd better stay north of Cape Cod



I doubt 1 in 100 boats in Charleston Harbor have any ground systems at all.
They all survive the summer storms just fine.

We do NOT have those blinding thunderstorms of the Northeast US or western
Florida, though. Ours are caused by localized thunderstorms that rise up
in huge thermals over the swamps just inland and the wind blows them over
us.

How about this?

http://home.maine.rr.com/rlma/Ground.jpg

I hauled out 180 feet of chain and removed my bilge storm chain locker for a
better look and measurements. This is close to scale.

The ground is shown in red. This would be about two square feet of 1/16"
copper glued to the hull and screwed in way of the ballast fill. A 1/2"
diameter silicon bronze bolt would go through the copper and hull. This is
the same cross section area as the stainless steel mast stanchion.

The connection between the mast stanchion and the through bolt would be a
1/8" copper bracket with bent flanges for resistance to the mechanical
forces of the charge. This would be machine screwed to the pipe stanchion
from the back.

A refinement would be to make the through bolt longer and fasten it to the
side of the bracket with through bolts for a more straight line electrical
path.

--
Roger Long

Roger Long wrote:
How about this?

http://home.maine.rr.com/rlma/Ground.jpg

I hauled out 180 feet of chain and removed my bilge storm chain locker
for a better look and measurements. This is close to scale.

The ground is shown in red. This would be about two square feet of
1/16" copper glued to the hull and screwed in way of the ballast fill.
A 1/2" diameter silicon bronze bolt would go through the copper and
hull. This is the same cross section area as the stainless steel mast
stanchion.

The connection between the mast stanchion and the through bolt would be
a 1/8" copper bracket with bent flanges for resistance to the mechanical
forces of the charge. This would be machine screwed to the pipe
stanchion from the back.

A refinement would be to make the through bolt longer and fasten it to
the side of the bracket with through bolts for a more straight line
electrical path.

Doesn't look too bad, definately better than leaving it alone. As I
mentioned previously, this is much like a HF grounding problem (except a
DC path is required and the expected current level. That would lead me
to suspect that multiple bolts between the copper bracket and the
grounding plate would be in order. Take full width copper plates bolted
on fore and aft of the support strut out to ground plates port and
starboard. If you can persuade the current to split fairly evenly you
gain *much* more protection from explosive events round those 1/2"
through hull bolts as resistive heating will be proportional to I^2. If
you manage to split the current evenly between four bolts, two each
side, the energy dissipated in each bolt will be reduced by a factor of
16.

I wouldnt bother with the longer bolts bent and bolted to the bracket,
You'd be better off with triangular pieces brazed accross the corner of
the bracket to its flange either side of each bolt, leaving just enough
room to get the end of a spanner in. If everything is nicely faired in
and you round off all sharp edges to the largest radius possible you
should have minimal structural and underwater damage.

There is likely to be at least *some* moisture behind the exterior
grounding plates so I would expect a steam explosion especially at their
edges. Screwing them into the ballast keel is probably not a good idea.
Drill and countersink holes in the plates *ONLY* to provide a key and
epoxy them into place? They will probably come loose at the edges in a
strike but hopefully will remain connected at the through bolts.
If you can keep the encapsulated ballast from being involved, you've
basically won.

Have you considerd that the odds are that you *WONT* have a startable
engine unless you can either hand start it or have a spare starting
battery kept fully isolated and a spare starter motor. Also you will
probably have damage to control cables and possibly to any metal fuel
lines depending on their proximity to other items.

I've seen photos of lightning damage to a mast with multiple holes you
could stick several fingers through down it for about a quarter of its
length so rig failure is also a real possibility.

Thanks, this is very helpful. I'd planned on the flanges being arranged so
that the nut of the through bolt is sort of in the end of a box. By
extending the flange against the hull and making the top and bottom edge
flanges triangular, I could get in two or more bolts. My problem is that
this all has to be done from one side so I can't put bolts forward of the
mast strut or main vertical plate.

If I keep extending the bolt flange along the hull back to add additional
bolts, do I run into a situation of diminishing returns?

It would be nice to simply duplicate the arrangement on the other side but I
have wires and plumbing running through that side of the bilge.

I know I'll still have a lot of damage in event of a major strike but I'd
like to be figuring out my next move sitting aboard the boat than swimming
or sitting in a dinghy waiting for the next bolt. Most boats that I have
heard of being struck in this part of the world had only electronics damage.
even without good protection, so something like this should heavily weight
the odds in my favor.

Is there any advantage or downside to making this conductor out of multiple
laminations of 1/16" copper sheet?

--
Roger Long

Roger Long wrote:

Thanks, this is very helpful. I'd planned on the flanges being
arranged so that the nut of the through bolt is sort of in the end of a
box. By extending the flange against the hull and making the top and
bottom edge flanges triangular, I could get in two or more bolts.
OK, Keep the box section but widen it vertically against the hull to
allow for two bolts. Add a rib down to the flange between the bolts.
After a trial fit has been done and all fixing bolts tightened to
conform it to the hull, take it out and braze or silver solder any joints.


My problem is that this all has to be done from one side so I can't put
bolts forward of the mast strut or main vertical plate.

Difficult. I presume there is a bulkhead in the way.
Can you get a strap round the front of the mast bolted to the copper
bracket either side sufficiently far out that it doesn't have sharp
bends in it? It wont have as good contact to the support post but should
help prevent flashover at the angle from the post to the bracket for
relatively little cost and difficulty of installation.

If I keep extending the bolt flange along the hull back to add
additional bolts, do I run into a situation of diminishing returns?
Yes. Two bolts a side is practical, three would be possible, more would
be of little benefit. Also the bolts should be as close as possible to
the main body of the flange and the same distance from it or the closest
will hog the current and the others be less effective.


It would be nice to simply duplicate the arrangement on the other side
but I have wires and plumbing running through that side of the bilge.
There is no reason why the other copper bracket cant have some big holes
in it for plumbing and other services, Just bolt braze or rivet a strap
of cross sectional area equivalent to the thickness times hole diameter
to both the top and bottom edges of the bracket.


I know I'll still have a lot of damage in event of a major strike but
I'd like to be figuring out my next move sitting aboard the boat than
swimming or sitting in a dinghy waiting for the next bolt. Most boats
that I have heard of being struck in this part of the world had only
electronics damage. even without good protection, so something like this
should heavily weight the odds in my favor.

Is there any advantage or downside to making this conductor out of
multiple laminations of 1/16" copper sheet?

Corrosion and getting even current sharing between the layers are
against you. Better to go thicker rather than thinner.

Dont loose sight of the fact that you *KNOW* you dont want any current
flowing down through the blocks of ballast in the keel and exploding the
possibly somewhat damp resin between them and blowing chunks of the skin
off. It also seems advisable to review your chain stowage. If its too
close to the foot of the support post, you will get side flashes out
through the hull via the chain.

I've looked over http://www.marinelightning.com/ and they dont seem to
say anything aboout the problem of a keel stepped mast (or a metal mast
support post) and the monohull installation link leads to a single
roughly annotated photo - not encouraging. Some good ideas and info
though especially for those of us with deck stepped masts without a
metal support post.

IanM wrote:

Can you get a strap round the front of the mast bolted to the
copper bracket either side sufficiently far out that it doesn't have
sharp bends in it?

I can't get to the front of the bracket without major surgery that would
compromise the boat's structural integrity as well as appearance.

I'm beginning to realize that this subject is so complex that only tests in
a high voltage chamber (which would cost enough to simply buy a high end
boat with protection already built in) will really answer the question but,
do you think this is worth putting in?

http://home.maine.rr.com/rlma/Ground.jpg

This is the earlier drawing with a top view added. The horizontal brackets
would be top and bottom. I recognize that the long tail is probably useless
for the primary current flow but will assist in attaching the copper outside
the hull and give me a point to lead bonds from the toe rail and other items
to.

I may be cooked anyway. The mast post ends in a plate lagged into the top
of the fiberglass ballast encapsulation so four sharp pointed lag screws
lead right down close to the encapsulated lead. I'm can't imagine now that
there won't be enough current flow left over, regardless of what I do, to
prevent something gross happening down in the keel area.

--
Roger Long