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From: dje@datacube.UUCP
Newsgroups: sci.electronics
Subject: Re: Lightning Rod Problem
Message-ID: <100500015@datacube>
Date: Thu, 9-Jul-87 13:41:00 EDT
Article-I.D.: datacube.100500015
Posted: Thu Jul  9 13:41:00 1987
Date-Received: Sun, 12-Jul-87 11:33:44 EDT
References: <204600003@prism>
Lines: 29
Nf-ID: #R:prism:204600003:datacube:100500015:000:1279
Nf-From: datacube.UUCP!dje    Jul  9 13:41:00 1987


I understand that this rule applies: 

A  direct  lightening strike  will be  drawn to  a thing  only if the
lightening was going to hit within a cone defined by  the thing's top
and a circle on the ground whose radius was that thing's height.  

That only counts for direct  strikes.   The Electric  fields near the
lightening get very high.  I was unfortunate to be out on Mass Bay in
an INTENSE lightening storm in a sailboat (40'  mast) with ungrounded
rigging.  No direct hit, but I saw giant bolts hit 100 feet  away.  I
recieved shocks from wet ropes and saw a 2" discharge from my hand to
boat hardware. New underware was in order.

I  agree  that  lightening  rods  dissipate  the  field  from  nearby
lightening, and I think they prevent damage from direct strikes.  

All masts should be grounded at *least* to a metal keel.   If you get
caught out in the water and you wonder if you're  grounded, shackle a
length of chain from a stay or shroud and let it drag in the water.  
Then stay away from everything.
 				Dave Erickson
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