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