(JAXAshby) wrote in message ...
pair of lox, a 5% chance of getting hit = a 95% of NOT getting hit.

A 5% chance of getting hit = .95 times .95 = a 90% of NOT getting hit even
once EITHER time in two tries.

a 5% chance of gettting hit = .95 times .95 times .95 times .95 = 81% of NOT
getting hit even once in FOUR tries.

by 8 tries the chance of NOT getting hit is only about 2 out of 3, by 14 tries
there is a better than even chance of being hit **AT LEAST ONCE**. by 30
tries, the chances of being hit at least once are 4 out of 5. by 50 tries,
chances of being hit at least once are greater than 15 out of 16. by 70 tries,
32 out of 33. by 90 tries, greater than 99 out of a 100.

that oak tree standing on the hill would be toothpicks by the end of the second
season.

Understand that in central Florida they receive more than 100 electrical storms
each year. a 5% chance of getting struck would mean central Florida has never
had trees.



How do you define "effective" area?
Your equation assumes that any lightning within the effective area of your
boat will strike your boat. If that were the case I'd be very afraid.

"Parallax" wrote in message
om...
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.

...

I found a web site that gave a strike rate of about .5 strikes/km^2/yr
but they did not say where they measured this. However, this means
that a lone sailboat with a mast 17 m tall would have a .35% chance
each yr of getting struck. This is an ideal situation though and may
not address the situation of a sailboat under a thunderstorm where the
strike rate/km^2 is hundreds of times higher. Because I know that the
strike rate in Fl is much higher than average, I'd want to double the
strike rate they give to be about 1/km^2/yr. This gives about a .7%
chance each yr of getting hit. Again, this does NOT address the
situation where you know the strike rate is much higer than average
(sitting under a storm). Based on math and observed strike rate, I
still think my estimate is good.








I am pleased to see that JAX can multiply. However, my analysis
assumes a LONE sailboat (or other tall object).

Now, I found a site giving the strike rate for Malaysia and remember
that only two places have a higher strike rate than Central FL,
Equatorial Africa and SE Asia. Malaysia has a strike rate of
25/km^2/yr. I remember that C. FL rate isnt too much smaller than the
highest so I assume 10/km^2/yr and you get (using my effective area)
of a 7% chance/yr of a LONE sailboat getting hit. I find this to be
VERY believable based on experience.

JAX, not all lightning strikes kill and not all trees hit are killed,
most are not. Perhaps you just are not familiar with being in a high
lightning environment. Around here, I can go into the woods and find
MANY trees that have been hit by lightning. This is particularly true
of tall cypress trees.
I have found web sites calculating strike probability and they all use
a formula similar to mine where effective area goes as the height
squared. However, none i have found specify the factor by wich to
multiply the height to account for electric field modification, they
just qualitatively say it goes as height squared or use empiracaly
derived effective areas.

I still find my calculation to be very reasonable.

yup, pair of lox, there ain't no trees in central Florida, and none either in
Malaysia or Equatorial Africa. All blasted to toothpicks by lightning hundreds
of thousands of years ago.

I am pleased to see that JAX can multiply. However, my analysis
assumes a LONE sailboat (or other tall object).

Now, I found a site giving the strike rate for Malaysia and remember
that only two places have a higher strike rate than Central FL,
Equatorial Africa and SE Asia. Malaysia has a strike rate of
25/km^2/yr. I remember that C. FL rate isnt too much smaller than the
highest so I assume 10/km^2/yr and you get (using my effective area)
of a 7% chance/yr of a LONE sailboat getting hit. I find this to be
VERY believable based on experience.

JAX, not all lightning strikes kill and not all trees hit are killed,
most are not. Perhaps you just are not familiar with being in a high
lightning environment. Around here, I can go into the woods and find
MANY trees that have been hit by lightning. This is particularly true
of tall cypress trees.
I have found web sites calculating strike probability and they all use
a formula similar to mine where effective area goes as the height
squared. However, none i have found specify the factor by wich to
multiply the height to account for electric field modification, they
just qualitatively say it goes as height squared or use empiracaly
derived effective areas.

I still find my calculation to be very reasonable.

Parallax wrote:
(JAXAshby) wrote in message
...
pair of lox, a 5% chance of getting hit = a 95% of NOT getting hit.
snip
I am pleased to see that JAX can multiply. However, my analysis
assumes a LONE sailboat (or other tall object).

JAX multiplying------ what a horrible thought ;-)

On 11 Jul 2004 10:05:27 -0700, (Parallax)
wrote:
... I found a site giving the strike rate for Malaysia and remember
that only two places have a higher strike rate than Central FL,
Equatorial Africa and SE Asia. Malaysia has a strike rate of
25/km^2/yr. I remember that C. FL rate isnt too much smaller than the
highest so I assume 10/km^2/yr and you get (using my effective area)
of a 7% chance/yr of a LONE sailboat getting hit. I find this to be
VERY believable based on experience.
///
I have found web sites calculating strike probability and they all use
a formula similar to mine where effective area goes as the height
squared. However, none i have found specify the factor by wich to
multiply the height to account for electric field modification, they
just qualitatively say it goes as height squared or use empiracaly
derived effective areas.

Here's a possible reason for some lightning estimators using height
squared.

Electric utilities use a cone of protection of 60 degrees included
angle beneath a ground wire.

If one used this 60 degree cone, the surface area "protected" by a
mast, in this case the area at risk, would be pi r squared,
where r is given by mast height X tan 30 degrees = 0.577 X m.h.
so pi r squared is pi X (0.577 X m.h) ^2 = 1.047 X m.h.^2

In other words, mast height squared is a reasonable area at risk
using the assumptions given above.
Then instead of a 7% per annum risk in Tstorms,
the risk is about 0.26% p.a.

Brian Whatcott Altus OK

Then instead of a 7% per annum risk in Tstorms,
the risk is about 0.26% p.a.

Brian Whatcott Altus OK


Brian, you confuse pair a lox when you talk rational.