[Frogwatch]

To try to get an order of magnitude probability of a sailboat getting hit by lightning, I assume the following:

An Average thunderstorm diameter of 12.5 km
An average of 500 cloud to ground lightning strikes /storm ( get these numbers from wiki)
The radius of influence of your mast is about 70 meters.
This simple models than says the probability of getting hit is simply the ratio of the area of influence under your mast to the area of the storm times the 500 strikes/per storm. It comes out to about a 1.5% probability of getting hit if you are a lone sailboat sailing under an active thunderstorm.
Of course, this model neglects a lot of things but it is probably reasonably accurate. I suspect the probability is a bit higher but probably no more than 5%.
So, how much of a chance do you want to take sailing under a storm? I have terrible luck so for me a calculated 1.5% is closer to 15% for most people.

 

[Uricanejack]

Well to start with it will vary depending upon the frequency of thunderstorms in the are you are sailing in.

 

[sandy stone]

Empirically, the odds seem to be a lot lower than that (thank goodness). Summertime around here sometimes seems like thunderstorm central, but I can only recall one sailboat getting hit under way in the last couple of decades. I've had some pretty uncomfortable times myself, with strikes on either side of the boat, but no direct hit. On the other hand, I know of several boats that have been hit at the dock (one of mine, in fact). Can't say what the difference might be.

 

[Frogwatch]

We are assuming you are sailing beneath a thunderstorm so the number of storms/yr does not enter this. Now, if you happen to go sailing during thunderstorms and you commonly venture under them then the probability of getting hit in a year would depend on the number of storms/yr.
I avoid T-storms to the point of not sailing in mid-summer, too hot anyway in FL to sail in summer.

 

[bacampbe]

The original post mentions 500 strikes per storm. I assume that's over the lifetime of the storm. If so, then the results are based on an implied assumption that you sail under the storm for the full lifetime of the storm. I imagine that's rarely the case. Storms move, and at least part of the time so do boats.

This would put the calculated odds off by a wide margin, even giving all the other assumptions the benefit of the doubt (e.g. strikes evenly distributed, all strikes in your radius-of-influence actually hit you.) You would need to consider the number of strikes over a period of time verses the time spent under the storm.

 

[Frogwatch]

bacampbe:

Right. I was simplifying as much as possible.
The reason why more boats get hit at docks is because most boats spend far more time at docks.
I actually think the 1.5% is low. If you actually stayed beneath a t-storm from start to finish, I think it should be higher. In fact, I think the radius of influence of your mast over a flat conducting plane (the water) should be higher and the probability goes as the square of this radius of influence.

 

[capta]

I can't count the number of times I have been in lightning aboard vessels of all kinds. Steel boats, wooden boats, steel masts, wooden masts, alloy masts and I've only been hit once, maybe (all the electronics gave up the ghost, but we found no damage aloft or to the vessel).
I've seen dozens of strikes around me within the horizon, in as many minutes. I've been the tallest thing for a few miles around and possibly a thousand. I've had lightning at sea so consistent that it was bright as day (at night) and I'm sure I could have read a book, though I was otherwise occupied. The lightning and thunder were simultaneous hundreds of times. I've been blinded for a few minutes by a strike so close my hair stood straight up.
I don't think it's possible to put numbers to this. You either get hit or you don't. I know sailing boats that have been struck several times, in different storms and others that haven't ever been hit.
I do, however, turn on my engine (not necessarily in gear) when I am in a situation where I might get hit, in the hope that the alternator's field might keep the vessel from becoming positively or negatively charged. I'm sure it's foolish and it may not have anything to do with my good luck, so far.

 

[TQA]

There are some figures around from one of the insurance companies [Boat US?] which say that a boat on the East Coast, Chesapeake to Florida, can expect to get struck every 10 years.

If this is true 8 years to my next one.

 

[tdw]

Been sailing boats off our coast since the mid 1970s. Have sailed down that coast with lightning hitting the water on either side of the boat, seen it hurling bolts horizontally across the sky, the night sky as bright as daylight, blah de blah de blah yet narry a hit.

Came home from a mini cruise January 2013, left boat on mooring, came back two weeks later to mass destruction ..... beyond AUD$40K.

You simply cannot set odds on lightning.

 

[JonEisberg]

You simply cannot set odds on lightning.

Not to mention, what's the point of trying to do so?

If the OP became convinced the odds were only 0.75% instead of 1.5%, would he then stop attempting to dodge thunderstorms, and sail blithely into them, instead?

 

[denverd0n]

Yeah, have to agree with JonEisberg. Not sure what the point is of trying to calculate the odds.

But beyond that, you acknowledge that your model neglects a lot of things and then conclude it is probably reasonably accurate anyway. I have to disagree. I don't see any reason at all to believe that your estimate is accurate. I suspect that of the many variables that your model neglects, some of them have a highly significant impact on the probability of a hit.

But in any case, a hit is a hit. Deliberately sailing into a thunderstorm is pretty foolish (for a lot of reasons, not just because of the lightening), and blithely assuming that you will never be struck just because the odds are low is about equally foolish.

 

[wind_magic]

Sailnet forum members have had boats hit by lightning.

It happens.

That seems like a high enough probability of it happening to believe it could happen to you.

 

[zeehag]

for a year we sailed blithely from inside one of those damnable tboomers into the guts of the next one.. was a truly electrifying experience. we did this for all except 2 weeks of a near year, being 11months. we sailed thru severe electrical storms(quote noaa) and ran from, extreme ones.
not once did we get hit.
no we had no lightning protection, as we saw first hand what happens when one has that....same boat in 4 yrs was hit twice requiring extensive haul and refit.
pays yer dough, takes yer chances....
yeah i would sail thru one again....with teeth clenched and bad words spewing righteously all the way thru.....

 

[RichH]

Ive been 'hit' three times on various boats, all mostly "RF events" (destruction of most of onboard electronics) not high powered 'amperage' events.

Good info here on the 'latest thoughts and theories' of lightning protection: http://www.marinelightning.com/index.html
Scroll down to "Principle Peer-reviewed science forms the basis" for the 'meat of the discussion'.
Also, see the commentary, based on insurance industry data, that multihull boats have a much higher incidence (2X) of lightning strikes as do mono-hulls.
Plus, the inference is that every boat sailing in lightning prone geographical areas has a very high statistical chance of getting 'hit' every 10 years.

 

[Frogwatch]

I calculate because I am an engineer and that is what I do.
I also think it is possible to get within an order of magnitude with a simple model.
I think my parameters are the greatest factors, if you disagree, say why.
If you disagree with my parameters, give your own.
I'd like to know how to figure the danger of being struck in a variety of conditions and this is the simplest start. Now, I'd like to get a more accurate answer by filling in some other parameters.

Some possible changes to make it more accurate:

I use the "rolling sphere" model of lightning strike to determine the "zone of influence". THis generally says 150-250' as the radius of this sphere. Considering that the probability varies as the square of this radius, it would be hlpful to be more accurate.
I think that for a lone sailboat under an isolated storm on a wide flat body of water far from anything, the mast height does not matter as long as it is very small in relation to the diameter of the storm. Do NOT extrapolate from this to tall trees or tall masts in other situations.
I can imagine that not all of a t-storm is "active" in making lightning so a better answer would use an active area.

 

[Ajax_MD]

To try to get an order of magnitude probability of a sailboat getting hit by lightning, I assume the following:

<yaddah yaddah>

Of course, this model neglects a lot of things but it is probably reasonably accurate.

ROFL!!!

Hey, we don't need no stinkin' data!

 

[Frogwatch]

If a pilot told you he had no interest in knowing anything about his probability of avoiding micro-bursts, you'd think him foolish. The same situation should apply here.

 

[caberg]

I don't think any amount of calculating probabilities that you do here will have any impact on whether you ever get hit by lightning or not, unless it means that you just never step foot on a boat. What would you do differently based on the % probability that you calculate?

Personally, I sail in the northeast with very frequent summer thunder/lightning storms. When they are forecasted, we keep an eye out. When we see one coming, we run for cover. If we get caught, we do our best to ride it out and keep everyone safe. Not sure how or why any probabilities would change my behavior.

 

[Frogwatch]

Ultimately, a good model might tell you how to avoid high probability of strike situations. Do you think people of the 1960s should not have modeled hurricanes because their models were poor? A model does not even need to be very good (in terms of predicting an accurate probability) if it can help predict higher probability circumstances of being struck.
Those who reject this exercise don't go deliberately sailing under t-storms so they are using their minds model to say "danger". Physics and math can give us even more info.

 

[Group9]

I would say the probability would fall somewhere between 0 and 100 per cent.



Honestly, I don't think there is a way to calculate it. There are just too many variables, and too many of them that you can't find a value for anyway.