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(Parallax) wrote in message . com...
(JAXAshby) wrote in message ...
they don't begin to get struck 1 time in 20 storms. not even close.

Out of curiosity, I did a quick back of the envelope estimate of the
probability of a lone sailboat getting hit by lightning in a
thunderstorm.

Assume LONE sailboat, Flat conducting ocean, assume the mast is well
grounded, assume lightning equally distributed over the thunderstorm
area.

Now, I have forgotten how to do this calculation (this used to be my
speciality) but I vaguely remember that a spike type conductor above a
grounded plane produces minimal effects more than 3X its length away.
This means that a mast produces an EFFECTIVE AREA (a) of pi*9*l^2
where l = mast length.

BTW, I work in meters.

As I write, a weak thunderstorm is passing over the bldg. lightning
rate seems low, less than once/minute and most are prob NOT cloud to
ground. However, I estimate wind at 40 kts.

Based on a few storms I have seen on Apalachee bay, I think the 5.8%
probability for those intense storms to be reasonable and I seriously
avoid them.

Strongest storms cover a larger area with greater wind. I have never
been in one of those but have watched them. The sky doesnt just get
dark, but turns a strange color. Intense strike rate for a few
minutes followed by a sudden increase in rain rate followed by a taper
off in wind and strike rate.

I assume a thunderstorm diameter of 4 km based on driving through one
two days ago for a total storm area of 12X10^6 m^2. I assume the
lightning strike rate is about 3/minute and the storm lasts for 40
minutes for a total number of strikes/storm (n) to be 120.

SO...the probability of getting hit is: P=n*a/A *L (L is your "luck
factor", 0L1 means you are either optimistic or lucky, L=1 means you
do not believe in Luck, L1 means you are pessimistic or unlucky, L=0
means you dont really sail). Top of my mast is 17 m above water for
an effective area of 7803 m^2.

So, P= 120*7803/16X10^6 *(L) = 585225X10^-6 * (L)= .058 * (L) or 5.8%
* (L).

Based on limited experience with games of chance, I estimate my L = 3
so my strike probability is 17.4%.

Seriously, the 5.8% chance shows why sailboats do not get struck more
often although they are the tallest things around.

OK, OK, I take back anything I said about wimpy thunderstorms up north
after viewing a series of websites with supercell storms over the
great plains states and all the way up to MN.