Lightning Protection questions
 

"Marty" wrote in message
...
Capt. JG wrote:
"IanM" wrote in message
...
Roger Long wrote:

I don't know why my first Google search missed this site:

http://www.marinelightning.com/

but it calls into question the whole idea of the central main
conductor.

I'm fortunate in having one of those aluminum toe rails that go bow to
stern on each side. It seems that I might be better off running the
heaviest wire I can between the port and starboard toe rails inside at
bow and stern and then bonding each chainplate to the toe rail and
running 4 ga conductors to each piece of underwater metal I can. I
have a number of unused through hulls that are capped. The
chainplates on my boat all end very close to the toe rail so charge
coming down the stays would likely jump that way even without bonding.

As I said earlier, If you let the lighting get below deck, you are
screwed and if down to bilge level ****ed unless its got somewhere to
go. For a powerboat or a sailboat with a non-conductive mast support
post, its probably practical to *NOT* have a central lightning
conductor, but where do you think the bulk of the lightning current is
going to go? Down a nice thick piece of low resistance aluminium bolted
inline to a heavy fairly low resistance steel pipe leading to the bilge
or down fairly high resistance shrouds and stays with rather dodgy
electrical contact at the top and bottom ends?

There is going to be *some* current down the stays so it would appear
prudent to bond the toerail to the shrouds, stays and mast foot, and
cross bond bow and stern, but then the problem is where do you encourage
the inevitable flashover from the toerail to the water surface to go? A
strap down the stem and each transom corner would be a good start but
few owners are going to tolerate external straps down from the
chainplates. I suppose you could trail a chain from each shroud while
berthed and if caught out in a thunderstorm.


From my manual:
22:00 LIGHTENING PROTECTION AND BONDING SYSTEMS

All Sabre yachts are equipped with a heavy duty lightening ground and
bonding system connecting all essential equipment to the keel using #8
gauge stranded copper wire.

22:01 BONDING SYSTEM: The bonding system provides low resistance to
electrical connections of all underwater fittings, fuel fill, fuel tank
and engine to the keel. This keeps all fittings at the same electrical
potential to minimize the effects of any galvanic or electrical corrosion
which may occur.

Any additional underwater hardware installed on the boat must be tied in
to the bonding system to maintain proper operation and protection from
corrosion.

The integrity and operation of the system should be checked each year at
launching and hauling times.

Refer to the lightening protection and bonding system diagrams in the
back of the Owners Manual for the wiring details of your boat.

22:02 LIGHTENING PROTECTION SYSTEM: The lightening protection system
provides a "cone" of protection around the boat in the even of a
lightening storm. Grounding wires of #8 gauge copper connect all chain
plates and the mast step to the keel.


#8? Ha, Jon, I've seen the inside of an underground vault with the walls
spattered with copper after a 75KA short vaporized copper bus bars 1/2'"
thick by 4" wide. That's one hell of lot of #8 wires in parallel. Imagine
what happens with surge that may exceed 200KA?

I go along with others that have suggested that lightning protection for a
plastic boat is probably an exercise in futility.

Cheers
Martin


No doubt. Sabre seems to think it'd be acceptable protection. I think I
don't want to find out.


--
"j" ganz @@
www.sailnow.com

Lightning Protection questions
 

IanM wrote:
Marty wrote:

Capt. JG wrote:

22:02 LIGHTENING PROTECTION SYSTEM: The lightening protection
system provides a "cone" of protection around the boat in the even of
a lightening storm. Grounding wires of #8 gauge copper connect all
chain plates and the mast step to the keel.



#8? Ha, Jon, I've seen the inside of an underground vault with the
walls spattered with copper after a 75KA short vaporized copper bus
bars 1/2'" thick by 4" wide. That's one hell of lot of #8 wires in
parallel. Imagine what happens with surge that may exceed 200KA?

I go along with others that have suggested that lightning protection
for a plastic boat is probably an exercise in futility.

Cheers
Martin

#8 is obsolete. #4 grounding wires are now called for. Also I'd lay
odds that the 75KA short lasted for several cycles of your 60Hz mains
before the breakers cleared it. It almost certainly had more than 1000
times the energy that a 100KA 1us lightning strike would dissipate in a
single #8 cable.

Doubtless you are correct, was probably 3 cycles; it's a suprisingly
common problem, circuit was a 600 amp 4.4Kv service, breakers that were
supposed to protect it were rated to break 10,000 amps. Problem was that
the supply was able to feed 75,000 amps, so the primary breakers tried
to trip but fried in the closed position, two cycles later the breakers
on the main feeder tripped. There are other problem with the lightening
strike, to start with duration is likely more than 1us, probably also
more than one stroke, usual pattern is several cycles, further 100KA is
likely a low estimate, some run higher than 500KA. Then just to
compound things, we're are talking voltages into the hundreds of
millions, and then we are generating plasmas, there are strange
electromagnetic effects, none of which are well understood or tractable
to simple modeling. Energy would be from 10 to 100 billion joules!
Your #4 is going to be toast. You need a cable thick as your arm to
guarantee that the cable wont fry, but with the other weird effects,
there is little guarantee that all of the energy will remain confined to
the path you are providing.

Cheers
Martin

If the protection system can prevent serious structural damage from 9
strikes out of 10 its obviously worth doing. If it reduces damage 50%
of the time so you dont have to abandon ship in the middle of a storm
its still worth doing if the cost is comparable to that of a liferaft.

Lightning Protection questions
 

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.

Lightning Protection questions
 

Capt. JG wrote:



No doubt. Sabre seems to think it'd be acceptable protection. I think I
don't want to find out.

Sound thinking!

Cheers
Martin

Lightning Protection questions
 

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

Lightning Protection questions
 

Larry wrote:
Wayne.B wrote in
:

On Sat, 8 Nov 2008 14:48:10 -0500, "Roger Long"
wrote:

I'm also thinking of some fresh water tripsafter my recent Hudson
experience and would like to take the boat south for at least one
winter.
There are almost no thunderstorms in south Florida from November
through May. We call it the dry season here for good reason.



Yeah, but Florida makes up for it in spades between June and
September....bigtime!

Indeed, there is a reason that one of the world's most prestigious
lightning research facilities is located there! The institution I work
for was thinking of renting some time there to research lightning and
it's effects on various airport grounding schemes, but being Canadian,
we didn't like the idea of summer in Florida....

Cheers
Martin

Lightning Protection questions
 

"Marty" wrote in message
...
Capt. JG wrote:



No doubt. Sabre seems to think it'd be acceptable protection. I think I
don't want to find out.

Sound thinking!

Cheers
Martin



Only after the fact. LOL

--
"j" ganz @@
www.sailnow.com

Lightning Protection questions
 

On Sun, 9 Nov 2008 20:17:04 -0800, "Capt. JG"
wrote:

"Marty" wrote in message
m...
Capt. JG wrote:
"IanM" wrote in message
...
Roger Long wrote:

I don't know why my first Google search missed this site:

http://www.marinelightning.com/

but it calls into question the whole idea of the central main
conductor.

I'm fortunate in having one of those aluminum toe rails that go bow to
stern on each side. It seems that I might be better off running the
heaviest wire I can between the port and starboard toe rails inside at
bow and stern and then bonding each chainplate to the toe rail and
running 4 ga conductors to each piece of underwater metal I can. I
have a number of unused through hulls that are capped. The
chainplates on my boat all end very close to the toe rail so charge
coming down the stays would likely jump that way even without bonding.

As I said earlier, If you let the lighting get below deck, you are
screwed and if down to bilge level ****ed unless its got somewhere to
go. For a powerboat or a sailboat with a non-conductive mast support
post, its probably practical to *NOT* have a central lightning
conductor, but where do you think the bulk of the lightning current is
going to go? Down a nice thick piece of low resistance aluminium bolted
inline to a heavy fairly low resistance steel pipe leading to the bilge
or down fairly high resistance shrouds and stays with rather dodgy
electrical contact at the top and bottom ends?

There is going to be *some* current down the stays so it would appear
prudent to bond the toerail to the shrouds, stays and mast foot, and
cross bond bow and stern, but then the problem is where do you encourage
the inevitable flashover from the toerail to the water surface to go? A
strap down the stem and each transom corner would be a good start but
few owners are going to tolerate external straps down from the
chainplates. I suppose you could trail a chain from each shroud while
berthed and if caught out in a thunderstorm.


From my manual:
22:00 LIGHTENING PROTECTION AND BONDING SYSTEMS

All Sabre yachts are equipped with a heavy duty lightening ground and
bonding system connecting all essential equipment to the keel using #8
gauge stranded copper wire.

22:01 BONDING SYSTEM: The bonding system provides low resistance to
electrical connections of all underwater fittings, fuel fill, fuel tank
and engine to the keel. This keeps all fittings at the same electrical
potential to minimize the effects of any galvanic or electrical corrosion
which may occur.

Any additional underwater hardware installed on the boat must be tied in
to the bonding system to maintain proper operation and protection from
corrosion.

The integrity and operation of the system should be checked each year at
launching and hauling times.

Refer to the lightening protection and bonding system diagrams in the
back of the Owners Manual for the wiring details of your boat.

22:02 LIGHTENING PROTECTION SYSTEM: The lightening protection system
provides a "cone" of protection around the boat in the even of a
lightening storm. Grounding wires of #8 gauge copper connect all chain
plates and the mast step to the keel.


#8? Ha, Jon, I've seen the inside of an underground vault with the walls
spattered with copper after a 75KA short vaporized copper bus bars 1/2'"
thick by 4" wide. That's one hell of lot of #8 wires in parallel. Imagine
what happens with surge that may exceed 200KA?

I go along with others that have suggested that lightning protection for a
plastic boat is probably an exercise in futility.

Cheers
Martin


No doubt. Sabre seems to think it'd be acceptable protection. I think I
don't want to find out.

Did Sabre consult directly with lightning to come to this conclusion?

How did they test the system?

Lightning Protection questions
 

Capt. JG wrote:

No doubt. Sabre seems to think it'd be acceptable protection. I think
I don't want to find out.

Sabre is, or was, simply following what the ABYC Standards said to do. It
was industry standard but now understood to be inadequate.

Don't find out:)

--
Roger Long

Lightning Protection questions
 

Wayne.B wrote:

That's a good point. I certainly wouldn't be in that part of the world any
other time.

However, we get some pretty good storms up here, complete with hail and
tornados. They usually weaken as they reach the coast but it only takes one
strike.

Exposure time is another issue. I plan to spend months at a time on this
boat which raises the risk far above daysailing and weekending when the boat
isn't occupied during severe weather and spends a lot of time in a marina or
mooring field where there are other targets nearby.

--
Roger Long

Lightning Protection questions
 

Good point. If I could replace my metal compression post with wood, I could
skip the step ground plate and focus on the stays. It would be easier to
install the ground plate than to do that though.

I'm beginning to get the picture. Lightning will go everywhere and the
charge can't be led. It's more a matter of creating shadows, gaps, and
regions of reduced current at critical points like people and watertight
boundaries.

--
Roger Long

Lightning Protection questions
 

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.

Lightning Protection questions
 

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

Lightning Protection questions
 

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

Lightning Protection questions
 

On Sun, 09 Nov 2008 20:31:02 -0500, someone posting as Marty purportedly
wrote:

#8? Ha, Jon, I've seen the inside of an underground vault with the
walls spattered with copper after a 75KA short vaporized copper bus bars
1/2'" thick by 4" wide. That's one hell of lot of #8 wires in parallel.
Imagine what happens with surge that may exceed 200KA?

I go along with others that have suggested that lightning protection for
a plastic boat is probably an exercise in futility.

So I'm guessing based on what I've read here in this thread, that hanging
a length of chain off the bottom of one of the upper shrouds into the
water -as suggested in a book I have called the "Emergency Reference
Manual"- would be one of those suggestions that would give a sailor some
sense of protection, without actually providing any.


--
150 days till re-launch (shut up Larry).

Lightning Protection questions
 

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.

Lightning Protection questions
 

"Roger Long" wrote in
:

Capt. JG wrote:

No doubt. Sabre seems to think it'd be acceptable protection. I think
I don't want to find out.

Sabre is, or was, simply following what the ABYC Standards said to do.
It was industry standard but now understood to be inadequate.

Don't find out:)


My Sea Ray jetboat was made to ABYC standards, too. It said so right there
on the little sticker. That's why the goddamned fuel tank inlet and vent
fittings were way up under the cockpit decking so you couldn't even see
them, much less change them or check them for tightness before the boat
exploded. To get to them, you simply disassembled the entire boat and took
the whole top off.....or you could take a rip saw and open a hole in the
deck but you'd have to be careful not to go 1/2" too deep or you'd be
cutting into the cheap milk bottle polyethelene plastic tank with 25
gallons of explosives inside held in with two tiny plastic angle brackets
eating into the soft plastic's aft end.

ABYC should be very proud.....

The stereo fuse holder was on the forward bulkhead of the engine
compartment held in with one screw.

Everyone should own one Sea Ray in their life......just one.

It's made by Bayliner....er, ah.....Brunswick....you know.

Lightning Protection questions
 

wordsmith wrote in news:ur6dnXDWjvz3
:

(shut up Larry).


Who? Me?

I'm not sleeping in it....(c;]

Lightning Protection questions
 

wrote in message
...
On Sun, 9 Nov 2008 20:17:04 -0800, "Capt. JG"
wrote:

"Marty" wrote in message
om...
Capt. JG wrote:
"IanM" wrote in message
...
Roger Long wrote:

I don't know why my first Google search missed this site:

http://www.marinelightning.com/

but it calls into question the whole idea of the central main
conductor.

I'm fortunate in having one of those aluminum toe rails that go bow
to
stern on each side. It seems that I might be better off running the
heaviest wire I can between the port and starboard toe rails inside
at
bow and stern and then bonding each chainplate to the toe rail and
running 4 ga conductors to each piece of underwater metal I can. I
have a number of unused through hulls that are capped. The
chainplates on my boat all end very close to the toe rail so charge
coming down the stays would likely jump that way even without
bonding.

As I said earlier, If you let the lighting get below deck, you are
screwed and if down to bilge level ****ed unless its got somewhere to
go. For a powerboat or a sailboat with a non-conductive mast support
post, its probably practical to *NOT* have a central lightning
conductor, but where do you think the bulk of the lightning current is
going to go? Down a nice thick piece of low resistance aluminium
bolted
inline to a heavy fairly low resistance steel pipe leading to the
bilge
or down fairly high resistance shrouds and stays with rather dodgy
electrical contact at the top and bottom ends?

There is going to be *some* current down the stays so it would appear
prudent to bond the toerail to the shrouds, stays and mast foot, and
cross bond bow and stern, but then the problem is where do you
encourage
the inevitable flashover from the toerail to the water surface to go?
A
strap down the stem and each transom corner would be a good start but
few owners are going to tolerate external straps down from the
chainplates. I suppose you could trail a chain from each shroud while
berthed and if caught out in a thunderstorm.


From my manual:
22:00 LIGHTENING PROTECTION AND BONDING SYSTEMS

All Sabre yachts are equipped with a heavy duty lightening ground and
bonding system connecting all essential equipment to the keel using #8
gauge stranded copper wire.

22:01 BONDING SYSTEM: The bonding system provides low resistance to
electrical connections of all underwater fittings, fuel fill, fuel tank
and engine to the keel. This keeps all fittings at the same electrical
potential to minimize the effects of any galvanic or electrical
corrosion
which may occur.

Any additional underwater hardware installed on the boat must be tied
in
to the bonding system to maintain proper operation and protection from
corrosion.

The integrity and operation of the system should be checked each year
at
launching and hauling times.

Refer to the lightening protection and bonding system diagrams in the
back of the Owners Manual for the wiring details of your boat.

22:02 LIGHTENING PROTECTION SYSTEM: The lightening protection
system
provides a "cone" of protection around the boat in the even of a
lightening storm. Grounding wires of #8 gauge copper connect all chain
plates and the mast step to the keel.


#8? Ha, Jon, I've seen the inside of an underground vault with the
walls
spattered with copper after a 75KA short vaporized copper bus bars 1/2'"
thick by 4" wide. That's one hell of lot of #8 wires in parallel.
Imagine
what happens with surge that may exceed 200KA?

I go along with others that have suggested that lightning protection for
a
plastic boat is probably an exercise in futility.

Cheers
Martin


No doubt. Sabre seems to think it'd be acceptable protection. I think I
don't want to find out.

Did Sabre consult directly with lightning to come to this conclusion?

How did they test the system?


Bzzzt... sorry. LOL

No idea... good question though.


--
"j" ganz @@
www.sailnow.com

Lightning Protection questions
 

On Mon, 10 Nov 2008 04:12:36 +0000, Larry wrote:

(Richard Casady) wrote in
:

What you want is a completely closed metal container. The charge will
stay in the walls of the container. They call this a Faraday Cage.

Casady



I thought they called that a "metal hull"....

Closed. A sub qualifies.

Casady

Lightning Protection questions
 

"Roger Long" wrote
I'm beginning to get the picture. Lightning will go everywhere and the
charge can't be led.

One thing to consider is that air is generally a good insulator with the
kind of electricity we're used to dealing with, but that lightning bolt just
travelled through half a mile or more of it to get to you, so you probably
shouldn't much count on being able to change its mind about where it's
going.

Lightning Protection questions
 

Lightning Protection questions
 

"Ernest Scribbler" wrote in
et:

"Roger Long" wrote
I'm beginning to get the picture. Lightning will go everywhere and
the charge can't be led.

One thing to consider is that air is generally a good insulator with
the kind of electricity we're used to dealing with, but that lightning
bolt just travelled through half a mile or more of it to get to you,
so you probably shouldn't much count on being able to change its mind
about where it's going.




What never ceases to fascinate me is the number of people who think
switching the switch on something to "off", making that miniscule gap in
the power switch so the 60 Hz AC line can't jump the gap, protects it from
the 400,000,000 volt, 500,000 amp jolt that just came 5 miles through the
air to hit it.

.......or how that same jolt is, somehow by magic, going to be BLOCKED from
tearing up the sensitive electronic device by a $2.79 white plastic block,
3x2x1 inches from Radio Shack, the electronic 7-11 store.

SURGE protectors must all be lightning protectors.......NOT!

Lightning Protection questions
 

Ernest Scribbler wrote:
"Roger Long" wrote

I'm beginning to get the picture. Lightning will go everywhere and the
charge can't be led.


One thing to consider is that air is generally a good insulator with the
kind of electricity we're used to dealing with, but that lightning bolt just
travelled through half a mile or more of it to get to you, so you probably
shouldn't much count on being able to change its mind about where it's
going.


Air is a far far better insulator than damp and salty GRP especially if
you can avoid corona discharge (no sharp points or edges on the
conductors and nearby objects). A lightning strike is the closest you'll
ever see to a perfect current source as it really doesn't care *what* it
goes through on its way to ground and is driven by such a high voltage
that it might as well be infinite so unless you shunt it aside
effectively, it *will* break down *any* insulation you can practically
put in its way.

Lightning Protection questions
 

Roger Long wrote:

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.

I see little benefit in the long diagonal strap. Current sharing with
the short strap wont be anywhere near equal. I know you have pipes and
wires the other side, but the big advantage of keeping the copper
bracket reasonably symmetrical (apart from one or more holes for the
wires etc.) port and starboard is the inductance from the change of
direction will partially cancel. If you try to take it out one side
only with too sharp a bend it *will* arc over to the other side and down
through the ballast. If its already got a heavy copper path out the
other side, it probably wont.

Several square feet of ground plate each side and you will have reached
the point of sharply diminishing returns. Just try not to leave the
boat in fresh water in storm country. If you need to do so and its
going to be on a shallow berth, take a strap down the side of the keel
to the bottom each side and pray.

As to the lag bolts, if there is any other way you could secure the
compression post foot like bonding it into place with Epoxy, do so.
Otherwise you are just going to have to gamble that you've provided a
good enough diversion path unless you want to bore through the ballast
and tap studs into it so its electrically bonded as well, then tap more
studs into it through the sides of the keel.

As long as nothings caught fire you couldn't put out, you have a means
of determining a course to make port (figuring your electronics is toast
and all compasses aboard have been magnetically damaged and are
untrustworthy) the underwater damage is less than you can cope with a
manual bilge pump, and you can still either make sail or get the engine
going you've succeeded in saving your boat, even though you may have to
stay on board pumping till you can be hauled out. Plenty of yachts have
been struck and survived. If your grounding system significantly exceeds
industry standards, with chain plates, toe rails etc. bonded, the odds
are in your favour. No guarantees though.

OTOH if you were designing a production series of yachts it would be
prudent to call in a specialist to do some heavyweight numerical
modelling and scale model testing to prove that it is effective enough
protection for 99.{as many 9's as you need)% of recorded lightning strikes.

Lightning Protection questions
 

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/

Lightning Protection questions
 

On Tue, 11 Nov 2008 01:28:39 +0000, Larry wrote:

"Ernest Scribbler" wrote in
news:MbOdnWJlr9NSLYXUnZ2dnUVZ_rHinZ2d@wvfibernet. net:

"Roger Long" wrote
I'm beginning to get the picture. Lightning will go everywhere and
the charge can't be led.

One thing to consider is that air is generally a good insulator with
the kind of electricity we're used to dealing with, but that lightning
bolt just travelled through half a mile or more of it to get to you,
so you probably shouldn't much count on being able to change its mind
about where it's going.




What never ceases to fascinate me is the number of people who think
switching the switch on something to "off", making that miniscule gap in
the power switch so the 60 Hz AC line can't jump the gap, protects it from
the 400,000,000 volt, 500,000 amp jolt that just came 5 miles through the
air to hit it.

......or how that same jolt is, somehow by magic, going to be BLOCKED from
tearing up the sensitive electronic device by a $2.79 white plastic block,
3x2x1 inches from Radio Shack, the electronic 7-11 store.

SURGE protectors must all be lightning protectors.......NOT!

Well, to be fair, they are honestly labeled, and commonly called
"Surge protectors", not Lightning Protectors. There are plenty of
surges other than a direct lightning strike that can damage
electronics, and surge protectors are a very cheap and relatively
effortless measure to help with some of those surges.

Lightning Protection questions
 

Jere Lull wrote:


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

The thing I've learned in this very interesting thread on via Google is that
lightning will follow every path; not just the path of least resistance.
There is so much current that even a small fraction can do enormous damage.
When it gets to the end of an ungrounded conductor, it's going to go
somewhere. The approach of leading it down the stays might work with a
non-conductive mast that didn't have any wiring in it but, as Ian points
out, when the largest conductor on the boat just ends either right above the
heads of people huddled inside (in the case of a non-conductive support
pillar) or at a non-grounded keel, bad things are going to happen.

There seems to be an inconsistency in the historical fear level of marine
lightning and current statistics. I suspect this is due to two main
reasons. First, up until about 40 years ago, the typical vessel had a
wooden mast with outside chainplates that lead near the waterline. This is
far from effective protection but may actually be as good as can be obtained
with secondary grounding of a metal mast. Second, boating in Florida and
other high strike probability areas has become vastly more common in the
same time period.

Most of the strikes I have heard of anecdotally in this part of the world
have only resulted in electronics wipe out. I've never heard of a sinking or
fatality in a sailboat in New England. Strikes clearly vary in intensity.
Some would probably sink a boat with a 4" diameter solid copper conductor
running to 50 square feet of ground plate. There is a huge probability
factor at work here.

The Sea Grant study

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

showed that 75% of Florida boats struck in salt water suffered no hull
damage, and less than 10% had watertight integrity breaches, a large
proportion of which were survivable. These translate into pretty good odds
for a boat operating in northeast waters or only in Florida during the dry
season.

In view of the difficulties doing anything clearly effective on my boat, I'm
now tending towards your quoted statement. There is a big element of "fun
for it's own sake" in these projects. I enjoy watching weather and
thunderstorms and that enjoyment would be increased by a lower anxiety level
about a strike. However, similar money and effort spent on similarly
interesting projects would probably increase the overall safety of my boat
more than grounding the mast.

If lighting wants to go in a straight line to large masses of metal, my mast
is probably somewhat grounded anyway. There is a lot of lead down there and
the keel is quite wide. Side flash would probably go down into that large
mass and spread out below the top of the encapsulation. There would still
be major flashes around inside the boat but it sounds like there would be
with any expensive and complex grounding plates I added as well. My
grounding scheme might well just attract the charge towards the thin part of
the hull. Damage down in the encapsulation would probably be major but
there would be so many paths that it probably wouldn't result in
catastrophic leaks. Leaking would take care of any fire that resulted in
the ballast area.

A small blood clot in a heart artery is probably an order of magnitude
greater in probability than a boat sinking strike in this part of the world
so perhaps I should just have two asprin and call back in the morning.

--
Roger Long

Lightning Protection questions
 

On Tue, 11 Nov 2008 01:28:39 +0000, Larry wrote:

......or how that same jolt is, somehow by magic, going to be BLOCKED from
tearing up the sensitive electronic device by a $2.79 white plastic block,
3x2x1 inches from Radio Shack, the electronic 7-11 store.

Lightning can induce surges in nearby conductors, and the do dads may
be of some value, if not surefire.

Casady

Lightning Protection questions
 

And one of those surges they protect from is the spikes caused by the power
grid response to strikes far from you cmputer. Turning off electronics is a
good idea, not because the little switch will protect from strike current,
as Larry points out, but because power instability from a strike across town
might overwhelm the surge protector of a dip as power is restored might let
the head of your hard disk briefly contact the platter surface (although
disk designs have greatly improved in this regard).

--
Roger Long

Lightning Protection questions
 

On Tue, 11 Nov 2008 07:46:38 -0500, "Roger Long"
wrote:

Jere Lull wrote:


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

The thing I've learned in this very interesting thread on via Google is that
lightning will follow every path; not just the path of least resistance.
There is so much current that even a small fraction can do enormous damage.
When it gets to the end of an ungrounded conductor, it's going to go
somewhere. The approach of leading it down the stays might work with a
non-conductive mast that didn't have any wiring in it but, as Ian points
out, when the largest conductor on the boat just ends either right above the
heads of people huddled inside (in the case of a non-conductive support
pillar) or at a non-grounded keel, bad things are going to happen.

There seems to be an inconsistency in the historical fear level of marine
lightning and current statistics. I suspect this is due to two main
reasons. First, up until about 40 years ago, the typical vessel had a
wooden mast with outside chainplates that lead near the waterline. This is
far from effective protection but may actually be as good as can be obtained
with secondary grounding of a metal mast. Second, boating in Florida and
other high strike probability areas has become vastly more common in the
same time period.

Most of the strikes I have heard of anecdotally in this part of the world
have only resulted in electronics wipe out. I've never heard of a sinking or
fatality in a sailboat in New England. Strikes clearly vary in intensity.
Some would probably sink a boat with a 4" diameter solid copper conductor
running to 50 square feet of ground plate. There is a huge probability
factor at work here.

The Sea Grant study

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

showed that 75% of Florida boats struck in salt water suffered no hull
damage, and less than 10% had watertight integrity breaches, a large
proportion of which were survivable. These translate into pretty good odds
for a boat operating in northeast waters or only in Florida during the dry
season.

In view of the difficulties doing anything clearly effective on my boat, I'm
now tending towards your quoted statement. There is a big element of "fun
for it's own sake" in these projects. I enjoy watching weather and
thunderstorms and that enjoyment would be increased by a lower anxiety level
about a strike. However, similar money and effort spent on similarly
interesting projects would probably increase the overall safety of my boat
more than grounding the mast.

If lighting wants to go in a straight line to large masses of metal, my mast
is probably somewhat grounded anyway. There is a lot of lead down there and
the keel is quite wide. Side flash would probably go down into that large
mass and spread out below the top of the encapsulation. There would still
be major flashes around inside the boat but it sounds like there would be
with any expensive and complex grounding plates I added as well. My
grounding scheme might well just attract the charge towards the thin part of
the hull. Damage down in the encapsulation would probably be major but
there would be so many paths that it probably wouldn't result in
catastrophic leaks. Leaking would take care of any fire that resulted in
the ballast area.

A small blood clot in a heart artery is probably an order of magnitude
greater in probability than a boat sinking strike in this part of the world
so perhaps I should just have two asprin and call back in the morning.

Lightning can just as easily strike the fiberglass hull at the same
time as it hits the mast, as it heads towards the water below it.
Lightning, as I have mentioned, has no brains. Who says it is more
likely to score a bulls eye on the top of the mast, just because it's
the highest point? It doesn't have that kind of accuracy, and it's not
a thin "arrow" of energy.

I've also heard of boats being struck and left with a myriad of
pinholes, rather than any large openings.

Lightning Protection questions
 

Ian,

Thanks again for all you've contributed.

I'm leaning away from doing anything at this point, aside maybe from some
more secondary bonding of the toe rail, simply because of the risk
statistics for the areas I plan to sail. I'm in the northeast. 20% of
boats in the water year round in Florida get struck. 90% of those only
experience electronics damage. Less than 10% develop leaks. From the total
safety aspect, my time and money are probably better spent elsewhere.

It's still on the table though and I had an epiffany looking at the boat
this morning. The mast is far enough forward that the keel situation is
actually like this:

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

(This is an update of an earlier drawing. This discussion is time dependent
as the links will expire anyway on 15 December 2008)

This is far enough forward in the keel that there probably isn't very much
ballast in that section. The structure is sufficiently massive and easy to
repair and work on that, if I do anything, I should probably excavate from
the outside and install suitably radiused and massive conductors closely in
line with the mast support. Two big advantages aside from not trying to
construct an intricate metal fabrication at arms length bent over a small
hatch:

1) I verify that I don't have pockets of water or uncured resin that could
create a massive steam explosion.

2) Main charge from mast is conducted below fiberglass bilge floor from
which it is less likely to turn 180 and flash back up into the boat.

The boat could use a bit more ballast so I would probably run something like
a piece of 3" bronze boat shafting right through the keel and then install
longer bolts in the mast support step that ran down to contact this. I
would then drill from each side at the shallowest angle I could for
something like 3/4" bronze boat shafting. The exit points would be lightly
epoxied over to keep out water. The front portion of the keel would be
copper sheathed, nice from an anti-fouling standpoint anyway, and the ends
of the conductors drilled and tapped with bronze machine screws run through
the copper for electrical contact.

This is how it would look:

http://home.maine.rr.com/rlma/Ground2.jpg

If I do run into ballast pigs, I'll just figure out a way to bond them
between the mast base and the copper ground sheet.

--
Roger Long

Lightning Protection questions
 

"Roger Long" wrote in
:

And one of those surges they protect from is the spikes caused by the
power grid response to strikes far from you cmputer. Turning off
electronics is a good idea, not because the little switch will protect
from strike current, as Larry points out, but because power
instability from a strike across town might overwhelm the surge
protector of a dip as power is restored might let the head of your
hard disk briefly contact the platter surface (although disk designs
have greatly improved in this regard).


Naw. The power supplies in your computer equipment are all switching
power supplies. Here's a block diagram:

LINE IN---rectifierbig capacitorsswitching transistors===*

*===high freq transformer===rectifiers===filter caps===voltage
measuring=*

*===regulated DC output to computer circuits from several
rectifier/filters on several windings of the HF transformer.

The output voltage measuring stage controls the pulse width of the IC
that drives the switching transistors. More load, simply widens the
pulse width fed to the switching transistors. That's how it regulates.

What's important is the first two stages. The AC line, WHATEVER YOU
FEED IT, is simply CONSUMED by the rectifiers...any frequency, any
voltage between about 80 and 250VAC, DC, 50, 60, 400, 1000 Hz, it
doesn't care. Whatever you feed it, sinewaves, squarewaves, triangle
waves, pure DC, is all converted to high voltage DC between about 150VDC
and 400VDC and any pulses, noises, crazy waveforms are simply consumed
charging the very large input filter capacitors which smooth them all
out into whatever unregulated DC just happens. The power supply cares
less unless the voltage is SO high it blows the switcher transistors or
big filter caps...destroying it. The range of nonsense you can feed it
and get pure, exact, DC out of it is simply amazing. IT'S NOT AN OLD
ANALOG POWER SUPPLY that operated over some narrow range of input and
waveform.

No matter even if there's some noise left on the feed DC input to the
switchers....THEY convert it all to really UGLY-looking, high frequency
pulses that vary in pulse width caused by the pulsing custom IC, in a 1
then 2 then 1 then 2 alternating pulsing of 2 sets of 1 or more pulse
transistors designed specifically for this high voltage switching at
several hundred kilohertz. Using high frequency, this allows them to
use a cheap, really light ferrite core transformer, instead of the 60 hz
soft iron monster you can hardly lift. The ferrite core makes the
pulses even uglier when they feed them out SEVERAL different windings to
different rectifiers and tiny capacitors. Tiny filter caps are fine
because we are filtering very high frequency ugly DC pulses...not those
60 Hz pulses of the old power supplies with LONG rest times between when
the filter caps had to run whatever the power supply was driving.

As you can see, there is a LOT of electronics between those power line
pulses you've been trying to protect it against, and that disk drive.
The switcher doesn't really care, unless lightning strikes OR POWER
STOPS! Filtering all the noise out of the input is just crazy. These
power supplies will even run on a hundred volts of Rock Music fed to the
input. I've seen it demonstrated! As long as the music doesn't STOP,
like the AC line must not STOP, you get perfect DC power to the
computer, or whatever it's driving.

If you're going to protect your computer, buy it an UNINTERRUPTABLE
power source...the kind with the battery powered inverter in it that
will keep AC coming no matter what, even power failures. A momentary
SAG in output voltage during a disk drive or memory WRITE is what kills
most computers...not power line surges that are very profitable to
outlet strip makers....and useless.

Have you noticed those REALLY LIGHT little wall wart power supplies for
your sellphone and mp3 players? Those, too, are switching power
supplies, not heavy 60 hz transformer/rectifier/filters. Their output
is perfect. Look closely at the INPUT voltage/freq specs and you'll see
something like 100-240VAC 50/60 hz. ANY power plug in the world will
work just fine by simply plugging them into a straight plug
adapter...115V/60Hz to 240V/50Hz...no problem...no voltage selecting.

As they are already rated for 240VAC, a peak voltage of around 350
volts...do you think ANY voltage spike that's not a lightning hit on
your 115VAC line will kill it? Nope...it won't. That silly little
power supply will keep on putting out pure DC while all the light bulbs
in the house explode....(c;]

Lightning Protection questions
 

Hey Larry. Thanks, this is good to know.

But, please, don't tell my boys. Thunderstorms are the only time I can get
them to turn the computers off and do something real:)

--
Roger Long

Lightning Protection questions
 

"Roger Long" wrote in message
...
Hey Larry. Thanks, this is good to know.

But, please, don't tell my boys. Thunderstorms are the only time I can
get them to turn the computers off and do something real:)


Like fuel polishing. Bwahahahhahahahaha!

Wilbur Hubbard

Lightning Protection questions
 

On Tue, 11 Nov 2008 19:47:03 +0000, Larry wrote:

"Roger Long" wrote in
:

And one of those surges they protect from is the spikes caused by the
power grid response to strikes far from you cmputer. Turning off
electronics is a good idea, not because the little switch will protect
from strike current, as Larry points out, but because power
instability from a strike across town might overwhelm the surge
protector of a dip as power is restored might let the head of your
hard disk briefly contact the platter surface (although disk designs
have greatly improved in this regard).


Naw. The power supplies in your computer equipment are all switching
power supplies. Here's a block diagram:

LINE IN---rectifierbig capacitorsswitching transistors===*

*===high freq transformer===rectifiers===filter caps===voltage
measuring=*

*===regulated DC output to computer circuits from several
rectifier/filters on several windings of the HF transformer.

The output voltage measuring stage controls the pulse width of the IC
that drives the switching transistors. More load, simply widens the
pulse width fed to the switching transistors. That's how it regulates.

What's important is the first two stages. The AC line, WHATEVER YOU
FEED IT, is simply CONSUMED by the rectifiers...any frequency, any
voltage between about 80 and 250VAC, DC, 50, 60, 400, 1000 Hz, it
doesn't care. Whatever you feed it, sinewaves, squarewaves, triangle
waves, pure DC, is all converted to high voltage DC between about 150VDC
and 400VDC and any pulses, noises, crazy waveforms are simply consumed
charging the very large input filter capacitors which smooth them all
out into whatever unregulated DC just happens. The power supply cares
less unless the voltage is SO high it blows the switcher transistors or
big filter caps...destroying it. The range of nonsense you can feed it
and get pure, exact, DC out of it is simply amazing. IT'S NOT AN OLD
ANALOG POWER SUPPLY that operated over some narrow range of input and
waveform.

No matter even if there's some noise left on the feed DC input to the
switchers....THEY convert it all to really UGLY-looking, high frequency
pulses that vary in pulse width caused by the pulsing custom IC, in a 1
then 2 then 1 then 2 alternating pulsing of 2 sets of 1 or more pulse
transistors designed specifically for this high voltage switching at
several hundred kilohertz. Using high frequency, this allows them to
use a cheap, really light ferrite core transformer, instead of the 60 hz
soft iron monster you can hardly lift. The ferrite core makes the
pulses even uglier when they feed them out SEVERAL different windings to
different rectifiers and tiny capacitors. Tiny filter caps are fine
because we are filtering very high frequency ugly DC pulses...not those
60 Hz pulses of the old power supplies with LONG rest times between when
the filter caps had to run whatever the power supply was driving.

As you can see, there is a LOT of electronics between those power line
pulses you've been trying to protect it against, and that disk drive.
The switcher doesn't really care, unless lightning strikes OR POWER
STOPS! Filtering all the noise out of the input is just crazy. These
power supplies will even run on a hundred volts of Rock Music fed to the
input. I've seen it demonstrated! As long as the music doesn't STOP,
like the AC line must not STOP, you get perfect DC power to the
computer, or whatever it's driving.

If you're going to protect your computer, buy it an UNINTERRUPTABLE
power source...the kind with the battery powered inverter in it that
will keep AC coming no matter what, even power failures. A momentary
SAG in output voltage during a disk drive or memory WRITE is what kills
most computers...not power line surges that are very profitable to
outlet strip makers....and useless.

Have you noticed those REALLY LIGHT little wall wart power supplies for
your sellphone and mp3 players? Those, too, are switching power
supplies, not heavy 60 hz transformer/rectifier/filters. Their output
is perfect. Look closely at the INPUT voltage/freq specs and you'll see
something like 100-240VAC 50/60 hz. ANY power plug in the world will
work just fine by simply plugging them into a straight plug
adapter...115V/60Hz to 240V/50Hz...no problem...no voltage selecting.

As they are already rated for 240VAC, a peak voltage of around 350
volts...do you think ANY voltage spike that's not a lightning hit on
your 115VAC line will kill it? Nope...it won't. That silly little
power supply will keep on putting out pure DC while all the light bulbs
in the house explode....(c;]



All that is swell, Larry, but most computers and Televisons don't get
fried through the AC cord. They get fried via network and POTS
connections.

Lightning Protection questions
 

On Nov 11, 7:46 am, "Roger Long" wrote:
If lighting wants to go in a straight line to large masses of metal, my mast
is probably somewhat grounded anyway. There is a lot of lead down there and
the keel is quite wide. Side flash would probably go down into that large
mass and spread out below the top of the encapsulation.

It's not that lightning wants to go straight. It's also not about
resistance. In an earlier question, you asked if a heavier gauge wire
would help. No. The concept is called wire impedance. Increasing
that 8 AWG wire to a heavier gauge does little to decrease impedance.
Shorter wire length - not wire diameter - makes better wire
conductivity.

Bending a wire increases impedance. A quarter round bent wire is an
inductor. Basically zero inductance to electricity such as 60 Hertz
AC. But a massive inductance to lightning.

How much lightning current can an 18 AWG lamp cord wire carry?
Something less than 60,000 amps. Lightning typically is only 20,000
amps. So we run larger 6 or 8 AWG wire to make it sufficient for even
largest lightning.

Routine is to have lightning strikes with no damage and no knowledge
that the lightning even struck. But that means some simple grounding
concepts as discussed in that article. If electronics are damaged,
well, electronics made a lower impedance connection to water; the
damage is how a weakness in that grounding is located and corrected.

Somewhere earlier, you worried about a 6" radius verses 8". Well,
that bend is an inductor trying to stop lightning currents. If
lighting does not travel through that bend, then what wire closer to
the cloud will arc to water (due to a sharper bend closer to water)?
IOW you are worrying about a minor thing. If that eight inch bend is
only feet from the grounding plate, then lightning will still go to
the grounding plate; not through the hull.

I did not see all posts. However there should have been a caution
somewhere about keeping those 8 AWG ground wires well separated from
all other wires. Even factory installers often don't understand this
concept which is why electronics damage occurs. If a ground wire is
bundled with other wires, then lightning induced surges is now on
those other wires (just another in a long list of reasons why plug-in
protectors also don't protection in the home).

Not having metal items bonded to that plate is the worst thing you
can do. Even simple lamp cord can conduct lightning because lightning
does not contain the high energy content so often assumed in myths.
How lightning gets to water is equivalent to "a battle is lost for the
want of a nail". It may not be the best, but it still may conduct
that current non-destructively into water.

One final point. In shallow water, lightning is seeking earth
beneath that water. Water is actually a less conductive material.
Lightning may even pass through the hull rather than use that ground
plate if bottom is closer to some other part of the hull. Just
another reason why we prefer that ground plate to be deeper; closer to
the bottom when in the shallows.

If is quite routine to have a direct lightning strike without even
any appreciable indication that the strike occurred. Lightning
strikes more often without any damage than you might imagine. Do
make metallic items (mast, rails) bonded to that ground plate. Then,
where possible, improve that connection by eliminating sharp bends and
separation from other wires.

Lightning Protection questions
 

On 2008-11-11 07:46:38 -0500, "Roger Long" said:

In view of the difficulties doing anything clearly effective on my
boat, I'm now tending towards your quoted statement. There is a big
element of "fun for it's own sake" in these projects. I enjoy watching
weather and thunderstorms and that enjoyment would be increased by a
lower anxiety level about a strike. However, similar money and effort
spent on similarly interesting projects would probably increase the
overall safety of my boat more than grounding the mast.

Oh, thank you! I nearly had a heart attack before I got to that part.

Lightning's scary. I lived in Clearwater, would spend hours on the
causeway watching the light shows over the lightning capital of the
world (Tampa).

But there are funner things to do since it seems the commercial
products seem to attract strikes.

--
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/

Lightning Protection questions
 

Jere Lull wrote:

But there are funner things to do since it seems the commercial products
seem to attract strikes.

I don't see a shred of evidence to support this. I think it more likely
that people who are on the water enough in frequent strike zones to be at
high risk install protection and therefore get struck more often simply
because they are at higher risk.

--
Roger Long

Lightning Protection questions
 

On 2008-11-12 05:25:05 -0500, "Roger Long" said:

Jere Lull wrote:

But there are funner things to do since it seems the commercial
products seem to attract strikes.

I don't see a shred of evidence to support this. I think it more
likely that people who are on the water enough in frequent strike zones
to be at high risk install protection and therefore get struck more
often simply because they are at higher risk.

My evidence is anecdotal only, primary one was one boat getting a
bottle brush installed by the factory team. Though the boat's mast was
relatively short compared to dozens of boats around it, it was the only
one hit -- a couple of weeks later. The device's insurance ensured they
paid nothing to get everything fixed, but they weren't able to get
enough of the systems up to use the boat that season.

Even land-based lightning rods have to be very carefully installed or
they attract strikes. (that's something I read in school, perhaps
connected to Ben Franklin.)

--
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/