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/