On Thu, 13 Nov 2008 18:11:35 GMT, Jere Lull wrote:

Given
unlimited money, we'd have a metal hull.

Somewhere around sixty or seventy feet and up, everything seems to be
steel and aluminum. My 22 foot fishboat is metal. It cost me two
grand.

Casady

Jeeezeus H Christ............what a thread!

This makes my worrying about a little rust seem like nuthin.

The more I learn about plastic boats the more I like steel.

Jere Lull wrote:
On 2008-11-13 03:40:42 -0500, "Edgar" said:

This is the first time anyone has mentioned the 'bottle brush' but I have
always believed that a spiky device at the very top of the lightning
rod is
essntial if it is to act effectively to reduce the possibility of a
dangerous strike.

That is one theory, the use of a "bottle brush" conductor is another;
there are others. Knowing a bit about electrical engineering,
electricity and electronics, I can follow the observations and math and
find good points in many of the theories advanced.

The problem is that no matter how long scientists (and snake-oil
salesmen) have been studying the problem, lightning strikes are
relatively random (determined by cosmic rays?) with the probability of a
strike in a particular location only slightly affected by man-made agents.

Well, there is the exception of the folks at U of Fl. who launch rockets
trailing thin wires into thunder clouds........


Other than that, fair enough..

Cheers
Martin

On Nov 13, 5:25*am, "Roger Long" wrote:
... but the gist from a quick skim was that some scientists now
believe that ground strikes are following *an ionization channel
opened up one of the high energy cosmic rays that are
constantly bombarding the earth. *The strike may divert to a
high object near the ground but the ray path could also lead
it to the water or a lower object.

Which says nothing useful. Cosmic ray does not construct a staight
conductive path through the air. Obviously lightning snakes in
various directions to earth; does not follow the straight path of a
cosmic ray. A microscopic path of ionied air might cause lightning
to snake slightly left rather than right. It is still constructing a
plasma path from cloud to earth because it must connect charges in
clouds (+ or 1) to charges on earth (- or+). If a conductive path
uses a boat, then a massive current later will follow that path
through the boat. Nothing will 'avoid' that strike.

Another myth promotes pointy items. Demonstrated in experiment is
that better protection uses blunt rather than pointy rods. Still when
lightning strikes, then either it does significant damage OR is
conducted harmlessly to beneath the boat. As the U of FL article
demonstrates, lightning can be conducted harmlessly if basic
guidelines are followed.

On Thu, 13 Nov 2008 20:34:47 -0000, Justin C
wrote:

In article , Vic Smith wrote:
On Thu, 13 Nov 2008 05:25:43 -0500, "Roger Long"
wrote:

I saw something in some science news on the net shortly before I started
getting interested in this subject, I'll have to find it again but the gist
from a quick skim was that some scientists now believe that ground strikes
are following an ionization channel opened up one of the high energy cosmic
rays that are constantly bombarding the earth. The strike may divert to a
high object near the ground but the ray path could also lead it to the water
or a lower object.

You don't get one track, you get an acre of them from just one
energetic cosmic ray. Within that two hundred feet, you would be
shaking the dice.

Casady

On Thu, 13 Nov 2008 22:51:09 -0500, Marty wrote:

Jere Lull wrote:
.... no matter how long scientists (and snake-oil
salesmen) have been studying the problem, lightning strikes are
relatively random (determined by cosmic rays?) with the probability of a
strike in a particular location only slightly affected by man-made agents.

Well, there is the exception of the folks at U of Fl. who launch rockets
trailing thin wires into thunder clouds........


Other than that, fair enough..

Cheers
Martin

Gotta be kidding. The statistics for tall buildings show a routine
series of strikes every year...

Brian W

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

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

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

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

Conductors should have a minimum 8" radius bend.

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

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

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

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

Another question:

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

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

I know of at least half a dozen sailboats that have been hit, one of
them twice on the same day. Only one sank and that was because the
lightning decided to exit through a plastic knot meter impeller
leaving a 1 inch hole in the bottom. It could have been plugged if
there had been anyone on board at the time.

What you are planning sounds like overkill to me, especially for
Maine. Where we live now there are thunderstorms almost everyday
throughout the summer but you don't hear about that many hits on
boats. Golfers seem to be the target of choice and they usually
fare poorly.

The reason it may be overkill is not because of the frequency of
lightning hits, but instead that his boat is already properly grounded.
Lightning will go through the path of least resistance, which in your
case is through the mast and keel. Not sure about the configuration of
your internal ballast keel, but if you are talking about completing the
connection of the mast to the keel, this is a good idea. My mast is
stepped on the cabin roof, so I ran a humungous copper cable from that
to my keel bolts, similarly to what you contemplate doing. On Lake
Michigan, I had a close lightning hit that traveled up my outboard to
the tiller I was holding and it knocked me clear across the cockpit. At
that point I installed my grounding cable.

I would not recommend any kind of rod atop your mast, as it may attract
lightning. If you are really concerned, have a backup antenna deck
mounted that you could switch to, if necessary.

Sherwin