[Rhodes22-list] sailing and lightning (long reply)

[Ronald Lipton]

I always enjoy the lightning threads, lightning is and is really not 
very well understood
even though it is one of the most spectacular natural phenomena. It 
inspires
me to go back and look at what is understood.  The charge
separation in clouds which causes lightning is due to movement of 
raindrops
or ice crystals in the up and downdrafts of the clouds.  The latest 
theory that I
saw speculates that small ice crystals are usually positively charged 
and the
larger crystals negative.  Updrafts separate the two species and 
generate the
potential difference which ultimately discharges between the cloud 
layers or
to the ground.  That is why lightning is closely associated with rain,  
the moisture
is the "fuel" of the electrostatic generator.  The rain itself has an 
effect on
the conductivity of the atmosphere which will effect the path of the 
stroke.  Dry
air has a breakdown voltage of ~10,000V/cm so normally conducting air 
would
only break down for strokes of a few hundred meters for megavolt 
potentials.
The ionization and humidity increase the distance to ~kilometers.

One of the most lucid descriptions of the phenomena associated with 
atmospheric
electricity is in chapter 9 of the Feynman Lectures in physics Vol II.  
It is worth reading
if you are curious and is not too technical.

Ron
On Jul 30, 2006, at 6:38 AM, Arthur H. Czerwonky we:

> Ron,
>
> While not followed in research, I have noticed a factor in lightning 
> storms that you have also possibly seen - the lightning will seem to 
> follow the heaviest concentrations of rain in its chosen path to the 
> ground/water.  Obviously, the easier path to follow in that 1000' or 
> so arc to the surface.  If the greatest density of rainfall is 
> avoidable, odds may decrease significantly, again I speculate.  A wise 
> mariner would prefer to avoid heaviest rainfall in any case.
>
> If a mast grounding was used , one of Thompson's posted papers 
> indicated 8 gauge wire was the normal cable used, and would melt under 
> a direct strike.  I have emailed him for more info, especially as his 
> posted research is a little dated.  I still wonder if a 6-8 gauge 
> copper, connected to the mast step area (well coupled at the hinge 
> bolt) and welded to a small copper plate would decrease the odds of a 
> bad outcome, given a direct strike.  BTW, I have no plans to research 
> this myself!  Who should we volunteer for this project, Ed?  After 
> all, he started this thread...
>
> Art
>
> -----Original Message-----
>> From: Ronald Lipton <rlipton at earthlink.net>
>> Sent: Jul 29, 2006 11:10 PM
>> To: The Rhodes 22 mail list <rhodes22-list at rhodes22.org>
>> Subject: Re: [Rhodes22-list] sailing and lightning (long reply)
>>
>> Rummy,
>>
>>   One of the interesting comments that Ewen thompson made on the
>> "Furling Sails" podcast, is that he knew of no lightning-induced
>> deaths on a sailboat.  I was surprised by this, but he claims to
>> have looked and found no cases. He believes that non-masted boats are
>> much more dangerous due to the chance of a direct strike near
>> the person.
>>
>> I don't think that having the mast keel stepped or not makes much
>> difference.  The charges on a metal object can move in response to
>> hugh fields in the storm and the most direct path to ground will
>> still be through the mast, followed by a sideflash to the water 
>> through
>> the air or the fiberglass. The grounding of the mast through the keel
>> only helps in providing a more direct path to the water "ground".  If
>> there is an insulating fiberglass layer between the mast/keel and the
>> water the lightning will punch a hole in it.
>>
>> I think going home is a good choice.
>>
>> Ron
>>
>> On Jul 29, 2006, at 8:27 PM, R22RumRunner at aol.com wrote:
>>
>>> Art and all,
>>> This is a topic that comes up at least once every year. There are a
>>> lot of
>>> people that have done extensive research on the topic and the general
>>> consensus
>>>  is that nobody can say with any amount of certainty which is the 
>>> best
>>> approach  for our boats.
>>> Since the R22 has a cabin top stepped mast and not a mast that goes 
>>> to
>>> the
>>> keel, I'm suggesting that it makes a lousy and probably an unlikely
>>> target for
>>> lightning. I sail on an inland lake which increases the odds that I
>>> will
>>> probably never get hit.
>>> Now, all that being said, I hate lightning and whenever there's even 
>>> a
>>> slight chance for a storm, I'm at the dock and going home.
>>>
>>> Rummy
>>> __________________________________________________
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>>>
>>
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