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First recorded activity by BoatBanter: Jun 2007
Posts: 739
Default Lightning Protection questions

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 Long


 
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