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.

"Roger Long" wrote in
:

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




I've been involved in tower grounding (just a mast 1200' high with no
sails, if we can help it) for decades in broadcasting. The AM towers
are series fed, meaning they are insulated from ground but have two
trailer hitch balls a few inches apart (far enough so the 5, 10, 25 or
50KW transmitters don't make them arc in the downpouring rainstorms.)
Looking around Jim Hawkins' broadcast transmitter website, you can learn
a lot about lightning grounding from the professionals:
http://www.hawkins.pair.com/radio.html

Let's look at the feedpoint of WFAN/WCBS AM stations whos twin 50,000
watt transmitters across the river from NYC share one tower. (The RF
comes out of the building on that copper tubing with the rain loop in
it.)

The 900', i think, tower sits on a large brown ceramic insulator. The
ring around the outside of the insulator has a lightning gap to that
metal ball hooked to the ground plate on top of the concrete base.
radiating out from the base are large copper ground straps that hook to
another ring, to distribute the hundreds of thousand of amps of current
from the stroke, and there is a ring of ground rods driven to bed rock
with a pile driver around that ring, the ring attached to the top of
them.

The key to these grounding systems is their SHORT, STRAIGHT AS POSSIBLE,
LOW IMPEDANCE path. Lightning is not considered DC in these designs.
It is a PULSE of power with an amazing bandwidth in frequencies. The
length of the conductors increases INDUCTANCE, which raises the
impedance to the very quick pulse. Impedance is our enemy. As it
rises, so does the voltage drop across it, raising the voltage on the
upper end of it. Any sharp corners MUST be avoided as that makes a
little 1 turn COIL raising impedance to the pulse. Ground strap must
CURVE around a large radius, as discussed in the article, to reduce
impedance and pulse voltage drop.

By the way, most big AM stations use the Harris DX-50 solid state 50KW
transmitters now. They use 55KW of power from the power company to put
out 50KW of RF to the antenna...This is one of the 230 switching modules
that actually provide the RF power:
http://www.hawkins.pair.com/wabcnow/wabcn14.jpg
All the cooling it needs is a few big muffin fans through those little
heat sinks to put out a blowtorch of AM radio power! Amazing
technology.

If you wanna see more, look he
http://www.hawkins.pair.com/wcbs_wfan.html
Most people have no idea where the signal comes from. They think it
comes from the studio where the stupid talking heads live.

http://www.hawkins.pair.com/wado/wadotowrleg.jpg
Here's a similar base at WADO, formerly WNEW. It has two lightning
balls across the massive insulator. The odd looking intertwined rings
are called Austin transformers. The RF won't flow between the rings
because they are far apart and provide fairly good isolation. What DOES
go across between these coils is 60 cycle AC power, magnetically
coupled, that light the tower lights you see day and night for those
folks riding to their deaths in airliners.

See all the direct, large ground straps heliarc welded to the ground
system under the tower? Low impedance...low voltage....only a few
hundred volts of pulse in a stroke to this huge tower.

http://www.hawkins.pair.com/wor/wor_tower08.jpg
This picture of the base of WOR's towers shows "Johnny Bells" and the
lightning balls to ground. Lightning flows out to the edge of the bells
then jumps the gap to the balls.

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

Your only hope is to BYPASS the lightning's current AROUND the
passengers and hull so it doesn't HAVE to jump THRU it, punching holes
in the expensive plastique. There are many "paths" to get the lightning
off the mast. The base of the mast must be connected to the sea as
short and direct as possible. From the above pictures, you can see how
big the conductor SHOULD be, but that's not very practical in most
boats. Keel stepped masts are easy. Copper straps to the inside of the
hull clamped between large stainless washers and 2 nuts where the
grounding block mounting bolts come through the hull. Coat it all in
your favorite sealant, but make sure you leave it where the sealant can
be shed so the grounding blocks can be replaced as they eventually will
be eaten.

I guess it's too ugly to expect painted straps down the OUTSIDE of the
hull to the same bolts UNDER the grounding blocks from the lower end of
the shrouds, another great path from mast to sea around the people, hull
and expensive electronics.

Backstay and Forestay ends also need grounding blocks underwater to
bleed off the charge around the ends of it.

Just dreaming....I've been knocked flat being between the backstay and
steering wheel in the way of lightning arcing between them. You'll
never forget it......so close.

On Mon, 10 Nov 2008 04:03:50 +0000, Larry wrote:

Let's look at the feedpoint of WFAN/WCBS AM stations whos twin 50,000
watt transmitters across the river from NYC share one tower. (The RF
comes out of the building on that copper tubing with the rain loop in
it.)

The WCBS/WFAN transmitters and tower are actually in New York City,
albeit the far north eastern corner, just south of mainland Bronx and
right on the edge of Western Long Island Sound. We moored our first
keel boat a few hundred yards from there after we bought it in 1971.

http://www.hawkins.pair.com/wcbs_wfan.html

Lat 40-51.589 Lon 73-47.126

You can see the tower and guy wires if you zoom way in with Google
Earth. Zoom back out and you can see the small bridge connecting High
Island with the north end of City Island.

Wayne.B wrote in
:

On Mon, 10 Nov 2008 04:03:50 +0000, Larry wrote:

Let's look at the feedpoint of WFAN/WCBS AM stations whos twin 50,000
watt transmitters across the river from NYC share one tower. (The RF
comes out of the building on that copper tubing with the rain loop in
it.)

The WCBS/WFAN transmitters and tower are actually in New York City,
albeit the far north eastern corner, just south of mainland Bronx and
right on the edge of Western Long Island Sound. We moored our first
keel boat a few hundred yards from there after we bought it in 1971.

http://www.hawkins.pair.com/wcbs_wfan.html

Lat 40-51.589 Lon 73-47.126

You can see the tower and guy wires if you zoom way in with Google
Earth. Zoom back out and you can see the small bridge connecting High
Island with the north end of City Island.



You should be able to put a large loopstick up on deck tuned to either
station, put it to a rectifier and recharge the boat...(c;

I know a ham who lives off the end of the old WKBW 1520Khz 3-tower
directional array in Hamburg, NY. There's a big open loopstick tuned
circuit in his attic that has powered the yard lights, his garage lights
and a couple of incandescents in the hallway for years. They all run
24/7 because if you turn one of them off, the impedance of the load
changes and blows all the other bulbs in the array....If one bulb blows,
they all blow....too funny.

If you have tooth fillings made with metal amalgams, you get to listen
to WWKB talk radio, these days, 24/7 with no radio at all..

And they told me RF radiation was dangerous to my health. My ham buddy
is 82 this year. He glows a little green in a darkened room, but other
than that he's fine....(c;]

PS - You adjust the loopstick's parallel tuning capacitor in and out of
partial resonance like a light dimmer to get the brightness you want.
Free power, just like Nikola Tesla envisioned.

Larry wrote:



I've been involved in tower grounding (just a mast 1200' high with no
sails, if we can help it) for decades in broadcasting. The AM towers
are series fed, meaning they are insulated from ground but have two
trailer hitch balls a few inches apart (far enough so the 5, 10, 25 or
50KW transmitters don't make them arc in the downpouring rainstorms.)
Looking around Jim Hawkins' broadcast transmitter website, you can learn
a lot about lightning grounding from the professionals:
http://www.hawkins.pair.com/radio.html

Thanks for the cool links Larry. The most dangerous job in America is
that held by the tower jockeys.

The impedance thing is the biggest factor, you ever think to calculate
the slew rate of a lightening pulse? Something like 50MV/uSec!

"Resistance is futile, but impedance is rather complex"

Cheers
Martin

Just a thought, has anyone looked at a faraday cage?
http://www.juliantrubin.com/bigten/f...periments.html

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.



Roger, I believe your question is:

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.

The bend is pretty critical. By making a turn you create part of a
transformer otherwise known as impedance or the resistance to an
alternating voltage. The tighter the bend the higher the impedance.
Also the higher the frequency the higher the impedance. Since a
lighting strike typically has very high energy, high impedance
components you are well advised to make the radius as smooth as possible.

Paralleling the run may help or may not. Without doing much more
research I can't tell. The problem would be if the two runs create a
field that would counteract the flow in the opposing wire thus again
increasing the impedance.

Larger wire helps but maybe not as much as you would think. At high
frequencies the current only runs on the outside of the wire in
something known as "skin effect." That is why they recommend braided
wire, much more surface area. BTW skin effect is caused by the parallel
paths in a wire from one side to the other, so you see that it can occur
in even small wires.

At radar frequencies they use hollow wires known as waveguide. I have
seen waveguide melted because of resistance heating due to a small dent
that caused some local impedance.

Probably not the answer you were hoping for. Sorry.

Roger Long schrieb:

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.

Hello,

the problem with the bends of the conductors is when the bend is to
tight, the lightning current will not follow the bend, it will leave the
conductor an flash thru the air in a direct line to the next best earth
point. Increasing the cross section does not help, you only can connect
more of these bends in parallel.

Bye

On 2008-11-08 12:40:47 -0500, "Roger Long" said:

This winter's major project is to add some serious lightning protection
to "Strider".

Nothing in this thread I can really tag into well....

Our surveyor was struck. He and boat were saved by an alert bridge
tender. As a result, surveyor joined ABYC and helped formulate the
guidelines.

From what I gleaned from him and other sources, I want to give a chance
for the charge to bleed to ground from the mast/stays, but if we are
hit, I want the lightning to stay OUTSIDE the boat.

At the moment, I only have the original charge-dissipation cables from
stays to bolts to our iron keel, a not-bad conductor, particularly as
it's got several square meters of surface.

But if I cruise towards any lightning-prone areas, I'll bulldog-clamp
big copper cables to the base of all stays, bolt zinc guppies to the
end (can never have too much zinc ;-) They'll be on deck as we move,
but dropped overboard when we stop or see a storm coming through.

I've seen too many "lightning arrestor" equipped boats, some installed
by the factory guys, get struck amidst "non-protected" boats with
higher masts.

In other words.....

No, no, No, NO, *NO*! Find something to occupy those idle hands that
will likely add positive survival probability.

--
Jere Lull
Xan-à-Deux -- Tanzer 28 #4 out of Tolchester, MD
Xan's pages: http://web.mac.com/jerelull/iWeb/Xan/
Our BVI trips & tips: http://homepage.mac.com/jerelull/BVI/