Lightning protection

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Lightning protection

Postby Georgs » Wed Jun 02, 2010 6:47 am

An organization called International Lightning Protection Association has taken issue with points made by Bob Austin in a post to Great Loop List. It's a good way to get a discussion started here about lightning and how to prevent damage and injury. What's your take on the subject?

Here's the email from Trang, the ILPA co-ordinator:

I come across a thread on this group from Bob regarding lightning protection for his boat:
http://groups.google.com/group/greatloo ... 1135e319a9

As far as Bob experience and question is concerned, I would like to submit the following ideas:

- A “good” lightning protection is a system that tends to eliminate or
a least reduce the lightning risk and damages. But there is no
certainty here facing a massive and unpredictable climatic phenomenon
and no system will ever offer a 100% lightning damage-free protection.

- The lightning dissipater installation does not deliver good results
since it is supposed to avoid direct lightning discharges and the boat
was struck twice.

- Lightning system includes the air terminal (capture of the direct
strike), the conductors and the ground system (metal plate embedded
into the hull for boats). The more conductive the installation is (ie.
length, section, materials and routing), the less damage the boat is
suffering. With a good conductivity, there are much reduced risks of
electrical arcing to surrounding metallic structures and surge. This
could be an explanation of the damages occurring on your smaller boat:
the lightning conductors are made of steel (dissipater), aluminum
(mast), copper and then “ground” plate: four different materials with
four different conductivity specifications leading to impedance
ruptures. The electrical continuity was “defective” and that could
explain the extensive damages caused by the discharges.

- Early Streamer Emission air terminal types are used to protect
larger boats (including Navy): these air terminals are providing a
large protection radius compared to a traditional rod. It allows the
protection of large surfaces/decks for staff/passengers even in
absence of high mast to be fixed (2 to 3 meters elevation pole only)

There is a lightning protection group (ILPA), if you need more advice
from expert I suggest you post your question over there:
http://groups.google.com/group/ilpa-int ... tion?hl=en

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Here's Bob Austin's post:

Lightning strikes occur onto boats in in fresh water, as well as salt or
brackish water. Protection is a very good idea--but of course the big
question is what is the best protection?

I had a large sailboat, which was in multiple areas of close lightning
strikes--one time over 60 strikes within a mile radius during an hour while in
Yugoslavia. That boat had two wooden masts, the forestay had continuity with
the fittings on the bowsprit, and going directly to a plate which was embedded
into the hull at the waterline (such that it was immersed all of the time. We
also rigged chains from the chain plates (fittings into the hull, which the
shrouds--wires which hold up the mast-- were attached). These chains were put
into the water on both sides, and from both masts (4 points). We had St.
Elmo's fire in the rigging, and strikes which were definitely bled off, or
conducted down these pathways. The only damage was the loss of several diodes
for wind instruments at the masthead. When I rigged a switch to disconnect
these wind instruments, the diodes no longer blew.

I had another slightly smaller boat, with a single aluminum mast--which we
fitted a Forespar lightning dissipater at the masthead--then a 3/4" copper
tubing directly from the base of the mast to a four square foot plate on the
bottom of the hull, right under the mast step. This is what appeared to be
best practices at that time. When the boat was sold, it had a lightning
strike which came from the water: a nearby power boat had a direct hit, with
substantial damage. The lobe of that strike was conducted thru the water to
the sailboat, and took out a diode on the engine alternator charge regulator,
and thus allowed 30 amps/12 volts from the 110 volt charger to travel
directly thru the ground system, and basically ate up all of the underwater
metal (Stainless and Bronze). Later that boat had two direct lightning
strikes to the mast/rigging--with over $30,000 each time.

What was the difference between the two boats? The first boat had a true
"cage" around it--the second boat, had a conductor directly from the top of
the mast (typical lightning rod) thru the center of the boat to the water.
Looking at the article cited yesterday--it became rather clear, why the first
boat was protected. There was basically a metal cage around the core of the
boat; more representative of a Faraday cage.

So, my suggestion would be to have lightning protection--but to run shrouds,
or some conductor outside of the boat, to ground points--at the waterline--and
around the periphery of the boat.

Bob Austin

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Georgs Kolesnikovs
Your host at Trawlers & Trawlering since 1997
http://www.trawlersandtrawlering.com
Your host at TrawlerCrawler.net since 2009
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Georgs
 
Posts: 126
Joined: Fri Mar 06, 2009 9:16 pm
Location: Frenchman's Bay, Lake Ontario

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