[Rhodes22-list] lightning protection

brad haslett flybrad@yahoo.com
Wed, 20 Nov 2002 18:04:47 -0800 (PST)


Roger, 

Thanks for the input.  My problem with your data is
that its based on land based structures.  I haven't
found any statistical data on water based structures
(ie. boats).  The marine insurance industry data
indicates that 10% of all cruising deaths are by
lightning strikes.  While that may not be a problem
for Rhodes 22 owners, since we don't make long
passages, it still leaves some room for doubt about
overnighting on fresh water lakes.  If you anchor in a
cove you've already violated your suggestion to stay
away from trees.  If you're in the middle of the body
of water (unlikely for most of us) you ARE the tallest
structure.  Which brings us back to the original
dilemma, what's the data on that?  In my part of the
South you will give up half the sailing season if you
stay home any time "a chance of isolated
thunderstorms" appears in the forcast.  I think the
bottom line on this issue is that there have only been
a few studies done and most of the articles written on
the subject keep citing the same sources.  I'm anxious
to read the ABYC and National Fire Code resources on
the subject but I suspect it will just be a re-hash of
the same insufficient data.

Brad Haslett
"CoraShen"
--- Al Miller <al.shell@verizon.net> wrote:
> Roger,
> 
> I like the way your explanation fits what I hoped
> was true!  I suppose
> my only ground problem will come from installing a
> ham rig in the boat.
> 
> Al-Mishka
> 
> 
> -----Original Message-----
> From: rhodes22-list-bounces@rhodes22.org
> [mailto:rhodes22-list-bounces@rhodes22.org] On
> Behalf Of Roger Pihlaja
> Sent: Tuesday, November 19, 2002 6:39 PM
> To: The Rhodes 22 mail list
> Subject: Re: [Rhodes22-list] lightning protection
> 
> 
> Guys,
> 
> I've been involved in the design & construction of
> several fairly tall
> structures over the course of my engineering career.
>  Some of these
> structures were distillation towers, which were 200
> - 300 feet tall &
> were handling large quantities of flammable,
> reactive chemicals.  So, we
> paid quite a lot of attention to lightning
> protection in these designs!
> 
> The American Society of Civil Engineers (ASCE) has
> done quite a bit of
> research into the effects of the height of a
> structure & grounding vs.
> the probability of it being struck by lightning.  We
> always used the
> ASCE design database.
> 
> Since I was downsized from my job at the Dow
> Chemical Co., I no longer
> have access to this database.  However, my
> recollection is that up to
> about 50 feet tall, the probability of a well
> grounded structure being
> stuck by lightening was statistically no different
> than level ground
> nearby.  Above 50 feet, the probablity of being
> struck increases
> exponentially to the point where very tall
> structures, like the Empire
> State Building, are struck at least once annually.
> 
> The ASCE data indicates that being poorly grounded
> tends to slightly
> decrease the probablity of being struck.
> 
> My take on all of this data is that our R-22's with
> deck stepped masts
> are poorly grounded.  Since the probability of the
> 28 foot tall masthead
> being struck is statistically no different than
> water level even if it
> were grounded, my answer is, "Do nothing to ground
> the boat."  The
> difference in my likelyhood of being struck is
> probably statisically
> insignificant, but intentionally not grounding the
> mast should tend to
> shift the probability slightly in my favor.  Plus,
> it's easier to do
> nothing.
> 
> One thing I do is disconnect the masthead VHF
> antenna at the base of the
> mast & turn off the on-board electronics during a
> thunderstorm.
> 
> My other advice is, stay away from tall structures
> like bigger sailboats
> & trees on hillsides.  Many trees on the shoreline
> have extensive root
> systems which extend quite a distance out into the
> water.  The roots are
> a rather poor conductor of electricity & lightening
> will tend to heat
> them instantly to incredible temperatures,
> potentially causing a steam
> explosion right underneath the boat!  This could
> ruin your whole day.
> Likewise, you don't want to be nearby a taller
> structure like a bigger
> sailboat.  A lightning strike puts out an incredible
> amount of EMP.  A
> nearby strike could inductively fry every piece of
> electronics on board
> your boat.
> 
> Trees, sailboats, the ground, & the water get struck
> everyday.  Use
> common sense & get off the water when lightning
> starts flashing if
> that's at all feasible.  But, if you're caught out
> on the water during a
> thunderstorm, just realise it's an act of God &
> there is very little you
> or I can do to prevent it.  Quit worrying about it. 
> It happens, but the
> odds of it happening to you are slim.
> 
> Roger Pihlaja
> S/V Dynamic Equilibrium
> 
> ----- Original Message -----
> From: "Rik Sandberg" <racerrik@rea-alp.com>
> To: "The Rhodes 22 mail list"
> <rhodes22-list@rhodes22.org>
> Sent: Tuesday, November 19, 2002 5:36 PM
> Subject: Re: [Rhodes22-list] lightning protection
> 
> 
> 
> <snip>
> 
> >
> 
> 
> _________________________________________________
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www.rhodes22.org/list


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