[Rhodes22-list] lightning protection

[Al Miller]

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



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