Lightening on Sunday - Eastern Solent - Decision?

[jlavery]

RORC race out through the Needles at night in the 80s. Massive thunderstorm, strikes into the water all around, none of the 40+ boats was struck. I was busy tangling kite halyards on the foredeck. It did focus my mind as to the fact that nearly everything I was handling was wet and connected directly to the top of the mast!

 

[srm]

Isn't it easy to calculate the distance of a lightning strike, regardless of whether it's dark or light? Just a case of applying a simple formula (though I forget what it is) to the time lapse between the flash and the bang? (Due to the huge difference in the speeds of light and sound transmission.)

I was busy taming the mainsail in a gusty thunder storm, lightening strikes just made a dramatic background. Calculating distance was not a high priority as I was more concerned about a rock that was near our intended track.

As to the simple formula, I had been told as a child to count the seconds between flash and bang to get the miles. However, having applied that more recently to pyrotechnic flash bang rockets when I know the approx location of the rocket it didn't work as it put the rocket too far away. Or perhaps my seconds were shorter than those used by the person who told me.

 

[jlavery]

Isn't it easy to calculate the distance of a lightning strike, regardless of whether it's dark or light? Just a case of applying a simple formula (though I forget what it is) to the time lapse between the flash and the bang? (Due to the huge difference in the speeds of light and sound transmission.)

Yes. Sound travels approx 1 mile in 5 seconds. So just count between flash and bang.

 

[blush2]

Looking at what's coming this way, I think we will be having a disturbed night here in the south west tonight.

Not sure it's going to hit the Solent.

 

[LittleSister]

As to the simple formula, I had been told as a child to count the seconds between flash and bang to get the miles. However, having applied that more recently to pyrotechnic flash bang rockets when I know the approx location of the rocket it didn't work as it put the rocket too far away. Or perhaps my seconds were shorter than those used by the person who told me.

You need to divide the seconds to get miles - by 5, according to jlavery in post no.23.

 

[srm]

You need to divide the seconds to get miles - by 5, according to jlavery in post no.23.

Yes, got that thank you.
However when working as a hydrographic surveyor I was more interested in the speed of sound in sea water. It varies with a number of factors and is a lot higher in the Persian Gulf than in the North Sea. We had difficulty calibrating the echo sounder on the first day working in the Gulf until I carried out a temperature/salinity/density profile to calculate the local speed of sound.

 

[Mark-1]

You won't be the only boat on the water, many with taller masts than yours.

Go. Otherwise you will never go anywhere.
The met office aren't showing any warnings at present and if they do I suspect that it is a low risk of them happening. Then add in the risk of being hit; so 1 million times 1 million makes the drive to the boat more dangerous ....

Thanks to everyone who replied. In the end we went, by then there was no lighting in the forecast and there was no hint of lightning IRL until after we were back. (Even then it came to nothing.)

I thought MM and BH nailed it. If you sweat every small risk you never go anywhere. The Solent was clearly going to be heaving in the heat and Bembridge was fully booked so it clearly wasn't worrying many other people I was clearly going to be comfortably the shortest mast on the milk run between Brading Haven and Bar Beacon. Plus I live in the area I sail and my house is taller than my boat and on higher ground. I could just have easily said "I'm scared of lightening hitting my house so I'm going out to sea on my short masted boat to get nice and low."

Thanks YBW for providing some welcome reassurance.

 

[Mark-1]

...and, after a weekend pondering about lightning I did wonder how attractive the mast really is to lighting. Assume the lighting is coming from 1500m and (in my case) the mast is 6m 68cm. The mast is making ~4.5pc percent difference to the gap and lighting doesn't seem to come down perfectly vertically anyway, so less than that. I'd love to know what difference that 4.5pc makes in terms of actually getting struck. (ChatGPT didn't know so maybe nobody does. )

If the mast doesn't make *that* much difference it would explain why places where lightning is far more common aren't overwhelmed by melted boats and dead sailors.

I can't find it now but a while back the Furled Sails podcast interviewed a guy call Dr. Ewen Thomson on the topic of Lighting and boats. Well worth a listen, still more questions than answers.

 

[Boathook]

@Mark-1 I seem to remember that the mast only attracts lighting if it is going to hit within a 'cone' round the boat. If your mast is around 7m tall and say a meter above the water line the cone will be roughly 8m diameter around the boat, nominally based from the mast location.

 

[Mark-1]

@Mark-1 I seem to remember that the mast only attracts lighting if it is going to hit within a 'cone' round the boat. If your mast is around 7m tall and say a meter above the water line the cone will be roughly 8m diameter around the boat, nominally based from the mast location.

Thanks, that sounds very plausible and explains why every trig point in the country isn't charred black and shattered!

 

[FairweatherDave]

Glad you got a sail Mark-1. I would have made the same call after the same anxiety. But if lightning is dancing anywhere nearby I don't want to be there and masts certainly attract lightning. We were in our Wayfarer on a lake in SW France and saw trouble approaching, wind died, skies dramatically changing. Outboard to the side of the lake and get family in a huddle about 30 yards away from boat. Skies open, wind, thunder and lightning. Then the most massive bang. Seriously count the members of the family to see they are all still there. Things calm down and return to the boat. Wind indicator no longer at top of the mast....looks like the pop rivets melted. I'm convinced we would all be dead if we had been in the boat.... Plenty of other boats half a mile away and lake surrounded by pines.

 

[Supertramp]

Many years ago I was motor sailing, at night, up the Sound of Jura. 42 ft sloop, steel hull, wood mast, standing rigging not insulated from the hull. A thunderstorm decided to take the same route up the sound and passed over us. We had to drop the mainsail as the wind increased and veered through about 500 degrees, or perhaps the compass card slowly spun around. Boat and mast were the highest points for a mile or so around us. I was standing on the coachroof, stowing the sail and feeling very exposed watching multiple lightning strikes hit the water. We were not struck though the guy on the helm noticed flickering on the backstay (perhaps St Elmo's fire?) but the electronics continued to work. It was not raining much so the strikes were probably further away than I thought: its difficult to judge in the dark.

I have not had that effect on a boat but several times up mountains in cloudy conditions I've heard and felt metal equipment humming and vibrating with presumably the electric charge in the air.

I think its a similar feeling of helplessness in the face of forces beyond comprehension. And if you stay put, is it enough to say "their mast is taller than mine" - your keel bolts or rigging tierods may be much nearer your keelbolts than theirs?!