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