Lightning

[capnsensible]

Standard 1st year electromagnetism question asks students to work out the potential difference as a function of radius from a tree struck by lightning, and come up with a safety recommendation. Which is "If you must be near a tree, stand facing it or away from it, so your legs are equidistant from the current feed"

Good cure for seasickness too.

 

[RobbieW]

Good cure for seasickness too.

Thought that was sitting under it ?

 

[AntarcticPilot]

Thought that was sitting under it ?

Ah, but if you sit under it, the potential difference across delicate parts might make you wish you hadn't! It might even make seasickness look like the soft option!

 

[johnalison]

There are indeed two sorts, convective/thermal and frontal. Convective ones are what you get when a summer cumulus goes mad and turns into a cumulo-nimbus with tremendous vertical winds in the upper section and consequently tremendous inflow around the base. In a frontal thunderstorm the vertical movement is started off by a cold front wedging in under and lifting warmer air up. That's enough to get unstable convection going, but not as viciously as in a cu-nim.

Good descriptions of both, including diagrams, at Thunderstorm

I usually associate cumulonimbus with the air moving inwards, often reversing the direction of the previous wind. On the occasion I described, the storm was approaching from the south and this was preceded by the wind in the same direction, which I remember well because the water turned black as it shot towards us, and the wind stayed in that direction, with the cloud and rain following.

 

[KeelsonGraham]

After a standard Saturday evening bareboat charter scramble out of Split, a group of yachts including us stumbled into a thunderstorm. One boat was hit and all the electrics and electronics were totally fried. No harm done to the crew, thankfully. But the rest of their charter was a miserable stay alongside (no replacement boat available).

Much later in the cruise we were clobbered by 3 successive downbursts of about 60 kt, all falling out of massive cu nim. But that’s a different story!

 

[ProDave]

Yes got caught out last year. Having a lovely sail until the wind stopped. Started motoring back to the harbour. Rain off to port side, no problem route to harbour clear. Only the storm moved and in a few minutes I was motoring in torrential rain, very low visibility, lightening striking all around and the only boat out with a big metal pole on top of it.

SWMBO looked out from the dry cabin "you look a bit worried dear" Understatement of the year.

When the storm cleared and I had not been fried, my dead reckoning steering was not far out and we were on pretty much the expected course for the harbour, where we tied up in brilliant sunshine but the storm was still rumbling in the distance.

 

[Biggles Wader]

Do steel ships often get hit by lightning?
I can find quite a few accounts of pleasure boats being struck but not one article on a boat with lighting conductors getting hit.
I quite like TNLI,s explanation about meta v grp and static voltages

My only experience of a lightening strike at sea was on a 12000 ton cargo ship at night in the Malacca strait. First we watched it strike another ship about a mile away and thought "they must have felt that". Then it hit our funnel with a huge bang followed by a ripping noise. It destroyed the main radio aerial but did little other serious damage. Very spectacular.

 

[FL390]

Winds associated with CB’s can move furiously out or in depending on the stage of development. Most will be familiar with the blast of cool air just prior to getting wet (gust front). The cells themselves tend to move roughly with the 10000’ ft wind. Selectable on various weather apps as the 700hPa level.

No idea about how best to avoid a strike. Scary stuff.

 

[ProDave]

After our "adventure" last year I debated afterwards if wrapping the anchor chain a few turns round the base of the mast and lowering the anchor into the water might have created an earth path in the event of a strike to prevent the shrouds, and more importantly the backstay that passes very close to the wet wooden tiller I was holding being the only path to ground.

 

[JNKScot]

After our "adventure" last year I debated afterwards if wrapping the anchor chain a few turns round the base of the mast and lowering the anchor into the water might have created an earth path in the event of a strike to prevent the shrouds, and more importantly the backstay that passes very close to the wet wooden tiller I was holding being the only path to ground.

Post #6

 

[oldharry]

Well the stom that hit the Solent 2 am this morning was certainly convectional. Chimet went from near zero to 50+knots in one huge gust, then remained around 30- 35 knots for the next hour before dropping back to a 4. Lightning was spectacular too, and my Rain guage registered 42mm of rain in a couple of hours, most of it in the first half hour.

I imagine anyone in the anchorage at E Head was kept fairly busy....