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#1
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LIGHTNING STRIKE PROBABILITY
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. 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. |
#2
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LIGHTNING STRIKE PROBABILITY
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. 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. |
#3
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LIGHTNING STRIKE PROBABILITY
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#4
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LIGHTNING STRIKE PROBABILITY
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#5
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LIGHTNING STRIKE PROBABILITY
dum dum, a 1 chance in 20 means a long oak tree standing on a hill, or a
telephone pole on the roadway would be splintered to toothpicks in a couple seasons. 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. |
#7
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LIGHTNING STRIKE PROBABILITY
parray, you take back everything you ever said about anything.
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. |
#8
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LIGHTNING STRIKE PROBABILITY
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#9
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I would have to give up sailing
if I thought I had a 5% chance (1 in 20) of any given storm hitting
me!!! OUCH, Paul Seriously, the 5.8% chance shows why sailboats do not get struck more often although they are the tallest things around. |
#10
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LIGHTNING STRIKE PROBABILITY
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. .... |
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