On Sun, 09 Nov 2008 18:25:21 GMT, (Richard
Casady) wrote:

On Sun, 09 Nov 2008 07:58:04 -0500, wrote:

The best thing you can do for lightning protection on a sailboat is
anchor near other boats with taller masts than yours, and THAT is also
foolishness and completely useless. It's only benefit is a little
humor.

Depends on the size of the boat, but hiding under a steel bridge might
work. I once hid my truck from golf ball size hail, under a bridge.
Talk about a piece of luck. I had stopped because the rain was too
heavy to see the road

The best thing for lightning is probably a metal mast bonded to a
metal hull. Guys used to go out in wood boats with wood oars for
power, and the target of choice would be a head. Smart targets would
lie down.

Casady

These days, it's not such a good idea to stop a boat under a bridge.
Homeland Security takes a very dim view of that.

"Roger Long" wrote in message
...
This winter's major project is to add some serious lightning protection to
"Strider". What I have now is probably sufficient to increase the odds
of being alive to climb into the dinghy and watch the boat sink but I'd
prefer to sail home. It's not a subject that comes up often for a
designer of metal vessels so I've been look around the web and learned:

The ABYS standards of 1 sq. foot of ground area and 8 GA conductors are
marginal and highly suspect.

Probably nothing feasible is going to protect a plastic boat in fresh
water. Although I'm generally in salt, I'd like to be ready to go up some
rivers.

Conductors should have a minimum 8" radius bend.

I've got a metal mast support strut that has sufficient through bolts to
the mast deck step to make it electrically continuous. This lands on a
wide, internal ballast keel. I plan to run flat copper straps about 1/16"
x 1/2" (approximate cross section of 4 ga wire) from this up each side to
6" x 24" bronze ground plates on each side of the hull. These will be
about 1/16" thick and through bolted to the hull at each corner. Inside,
there will be straps under the bolt heads in an "X" pattern with the strap
from the mast strut lead to the center. There will also be a 4 Ga wire
or strap from the engine block to one of these plates to help protect the
engine bearings.

Comments welcome on this conceptual plan which will also include other
secondary bonding additions as recommended by ABYC.

Here's my main question for someone who understands high voltage better
than I do:

I only have 6" under the cabin sole. How critical is the 8" bend? Can I
compensate for the tighter radius by increasing the conductor cross
section? How much? The turn is more than 90 degrees because the straps
have to run back up the hull deadrise about two feet to where I can locate
the plates and through bolts. I don't think putting the plates on the
keel sides is feasible.

Another question:

Is the standard metal rod VHF antenna at the top of the mast with the
typical metal can on a bracket riveted to the mast a sufficient air
terminal or should I add a dedicated rod?

I have no illusions about having any electronics working after a strike on
a 32 foot boat but replacement of my minimalist outfit wouldn't break me
financially. I'd just like to be alive with a working engine and
watertight boat.


To understand lightning you've got to understand why it strikes. You need to
"see" the world how lightning sees the world.

You get an unbalanced electrical charge between the clouds and the water.
Like all current, lightning takes the path of least resistance. This may or
may not have anything to do with height of mast. Height of mast and material
of mast and grounding of mast all have little to do with how lightning
"sees" the best path to ground.

The purpose of all the bonding and grounding is to bleed off charge slowly
before it builds up to a great enough extent to arc from above the boat. A
properly grounded GRP sailboat will be seen by lightning potential directly
over it as sitting in a valley. One not grounded at all will be seen as
sitting atop a hill. Again, it's not distance I'm talking about but
resistance in the path to ground. An ungrounded boat does not bleed off
potential. It spikes it up.

The trouble with grounding your boat properly is the slow bleeding off of
the charge imbalance can actually, in some cases, prepare a lower resistance
path to ground as charge is already moving that way. While it may thwart
lightning strikes from directly above, should lightning strike at a 45
degree angle, for example, it may well strike a well-grounded boat and not
strike an ungrounded boat anchored several boat lengths away.

But, a properly grounded boat will suffer less damage as the voltage will
not build up as much because the current (amperage) will flow easier to
ground. An ungrounded boat, though less likely to be "seen" by lightning
will, if struck, suffer more damage because the voltage will build higher
and the resultant amperage will also be higher.

My boat is totally ungrounded and in over 25 years has been struck only
once. I was aboard and all kinds of bad stuff happened. There was a zzzzzzt
and a huge crash simultaneously. Then a series of gun shots as ball
lightning went arching and dancing around everywhere inside. I was forward
lying in the v-berth. One ear on the pillow and the other up. It was
temporarily deafened for a couple days in the upper ear and had extensive
ringing but the hearing came back. I think I was knocked unconscious for a
couple of minutes. My hair smelled burnt.

Every wired electronic device but one GPS was cooked. Solar panels were
fried from the inside out. The wiring harness was cooked. All the lights
burned out. A charred hole the size of a walnut was blasted out of the GRP
ceiling where the cabin light wires were encapsulated. The backstay where it
split was burned in two on the port side where current arched from it to the
outboard motor the foot of which was in the water acting as a ground. The
current jumped from the backstay to the tiller handle and cooked the wiring
and throttle cable - burned them to a crisp. The plastic fuel tank had black
marks on it but wasn't burned through. The ignition was not ruined, however,
probably because most of it is under the metal flywheel. The base-loaded VHF
antenna at the mast head was an empty shell. The mast wiring inside was all
cooked. The depth sounder transponder was fried. Bottom paint was blasted
off the outside of two of the bronze thru hulls. The keel bolts above the
GRP floors were blackened. The boat was full of smoke. A bottle of brandy in
the undersink galley locker had burst and was burning in the bilge. The
Adler Barbour fried. The secretary at a nearby marina saw the strike. She
said is was very large and lasted seconds hitting again and again.

It cost over 4,000 dollars not counting my labor time to repair it all.
However the good news is the cast iron keel took the brunt of it with paint
and epoxy coating blasted off in several fist-sized places. The hull at the
water line took no damage. No leaks as a result. No hull damage. There was
some deck damage at the foot of the mast were the current actually passed
through to get to the wood enclosed steel post that supports the deck
stepped mast foot and then to the keel bolts.

The choices as I see them are these:

a) Bond and ground your boat well and be prepared to be hit more often but
with less damage.

b) Don't bond and ground and your boat will be struck less often but with
more damage.


b) has been and will continue to be my choice as proper grounding and
bonding can only really be done during the construction process. Once a boat
is built too much stuff has to be torn out to do the job right.


Wilbur Hubbard

On Sat, 8 Nov 2008 12:40:47 -0500, "Roger Long"
wrote:

This winter's major project is to add some serious lightning protection to
"Strider". What I have now is probably sufficient to increase the odds of
being alive to climb into the dinghy and watch the boat sink but I'd prefer
to sail home. It's not a subject that comes up often for a designer of
metal vessels so I've been look around the web and learned:

The ABYS standards of 1 sq. foot of ground area and 8 GA conductors are
marginal and highly suspect.

Probably nothing feasible is going to protect a plastic boat in fresh water.
Although I'm generally in salt, I'd like to be ready to go up some rivers.

Conductors should have a minimum 8" radius bend.

I've got a metal mast support strut that has sufficient through bolts to the
mast deck step to make it electrically continuous. This lands on a wide,
internal ballast keel. I plan to run flat copper straps about 1/16" x 1/2"
(approximate cross section of 4 ga wire) from this up each side to 6" x 24"
bronze ground plates on each side of the hull. These will be about 1/16"
thick and through bolted to the hull at each corner. Inside, there will be
straps under the bolt heads in an "X" pattern with the strap from the mast
strut lead to the center. There will also be a 4 Ga wire or strap from the
engine block to one of these plates to help protect the engine bearings.

Comments welcome on this conceptual plan which will also include other
secondary bonding additions as recommended by ABYC.

Here's my main question for someone who understands high voltage better than
I do:

I only have 6" under the cabin sole. How critical is the 8" bend? Can I
compensate for the tighter radius by increasing the conductor cross section?
How much? The turn is more than 90 degrees because the straps have to run
back up the hull deadrise about two feet to where I can locate the plates
and through bolts. I don't think putting the plates on the keel sides is
feasible.

Another question:

Is the standard metal rod VHF antenna at the top of the mast with the
typical metal can on a bracket riveted to the mast a sufficient air terminal
or should I add a dedicated rod?

I have no illusions about having any electronics working after a strike on a
32 foot boat but replacement of my minimalist outfit wouldn't break me
financially. I'd just like to be alive with a working engine and watertight
boat.

Wear a tin-foil hat if it stops you worrying..
http://www.google.co.uk/search?sourc...ng+cosmic+rays

On Sat, 8 Nov 2008 12:40:47 -0500, "Roger Long"
wrote:

I'd just like to be alive with a working engine and watertight
boat.

The wise Craptain Neal filled his boat with empty bottles and
inflatable dolls so that it was unsinkable.(like the Titanic)

"Roger Long" wrote in
:

s the standard metal rod VHF antenna at the top of the mast with the
typical metal can on a bracket riveted to the mast a sufficient air
terminal or should I add a dedicated rod?

I have no illusions about having any electronics working after a
strike on a 32 foot boat but replacement of my minimalist outfit
wouldn't break me financially. I'd just like to be alive with a
working engine and watertight boat.

--
Roger Long



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

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

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.