Sailing in thunder & lightening...

sighmoon said:
I think not.
The webcast chap said holes in boats, caused by lightening are at the waterline, so my understanding is that the voltage is between the sea surface and the clouds. Zilch below.

What a great thread this has turned out to be - I've learned loads (except how to make my boat lightening safe)
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I am told the most common cause of sinking is firstly through hull trasnducers, usually plastic, so instantly vaporized, and metal skin fittings being blown out and /or vaporised.
 
oldharry said:
I am told the most common cause of sinking is firstly through hull trasnducers, usually plastic, so instantly vaporized, and metal skin fittings being blown out and /or vaporised.
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Many years ago there was a Hirondelle Cat sunk in Poole on it's mooring for no apparent reason, until they found the echosounder transducer had been blown out of the hull. This was after a major thunderstorm and the assumption was that a lightning strike had done the dirty deed.
 
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If you're in the Solent area you should have a decent cell phone signal. If you have a smartphone then there's some excellent apps available that are basically weather radar images overlaid on Google maps. I use Rain Alarm Pro (Android) but Buienradar is pretty good - they'll give you a good idea of any cells approaching a lot of the time as well as the general activity in the area which can help with the decision-making.

If you've got a laptop and dongle then there's plenty of weather radar and thunderstorm plotters on the web - http://www.nowcast.co.uk/lightning/ is one.
 
I've always assumed that the trick with lightning was to make sure it had a path to earth (sea) without going through anything structural or below the waterline so not the keel bolt, prop shaft, etc. and that was the theory behind running a line from the shrouds into the oggin. I think the assumption is that your rigs probably gone no matter what you do if your struck.
 
I was always told that the lightening conductor is one of the best examples of something being named INCORRECTLY. If the lightening actually strikes, then the conductor isn't going to make much difference. The idea of the conductor is to discharge the leader BEFORE it turns into a lightening strike. It is NOT there to conduct the actual lightening strike! Hence the misnaming allegation.

Of course, this doesn't quite square with D Thomson's view - but he does own the company selling the product.

I now am not quite sure who to believe.
 
A 'lightning conductor' is surely just that. A heavy copper ribbon designed to conduct lightning away from or past the building it is there to protect, in the event of a strike.

Other protective devices are intended to make it difficult for the leader to form in the first place, usually by spreading the charged area out, so it cannot concentrate at one point sufficiently to start to build up a leader prior to a strike.
 
oldharry said:
A 'lightning conductor' is surely just that. A heavy copper ribbon designed to conduct lightning away from or past the building it is there to protect, in the event of a strike.

Other protective devices are intended to make it difficult for the leader to form in the first place, usually by spreading the charged area out, so it cannot concentrate at one point sufficiently to start to build up a leader prior to a strike.
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I was told that the conductor was to dissipate the leaders - thus preventing a strike occurring. A full on lightening strike melts lots of things, but I am no expert on the subject - just quoting from what I have read in the past...
 
I remember looking at the lightning conductor for St Michaels Tower, on top of Glastonbury Tor ( it would be hard to find a more prominent 500' high spot, surrounded by the flood plain of the Somerset Levels ).

The conductor was a steel strip, from memory about 2" wide by 3/4" thick, running from above the tower, down the stone wall and deep into the ground.

It was incredibly twisted and buckled, looked like a bit of a wrecked battleship which had received a good few heavy hits - I thought to myself ' if that's a working conductor, I'd hate to see an underspecified one !'
 
Well the good news is that we had a cracking days Sailing, and zero thunder, no rain, just some lovely sunshine, some F3 & 4's, and lunch at the folly.

Smiles all round...
 
john_morris_uk said:
I was told that the conductor was to dissipate the leaders - thus preventing a strike occurring. A full on lightening strike melts lots of things, but I am no expert on the subject - just quoting from what I have read in the past...
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It's still not fully understand by anyone as far as I know but you're definitely right, the full welly of the lightning strike doesn't normally go through the Lightning Conductor as that would simply vapourise in a decent strike. Lightning creates an ionised path through the air and pretty much anything else that gets in the way the way. One thing the lightning conductor does is ensures that the charge at the top of the building is the same as the ground around it - that makes it no more attractive than the ground around it. Lightning doesn't naturally take the shortest route - it takes the path of least resistance. If a building or similar does get struck the Lightning Conductor should steer the strike down that path. Some strikes are pretty much fully dissipated by the time they reach the ground (this is relative of course - it doesn't mean it's harmless, just that it may not dissolve everything in it's path). Others do vapourise the conductor and a few bits around it but they don't run through RSJ's or steel rod in reinforced concrete, which is the real danger of course..

The general theory with aircraft is to do everything possible to avoid the aircraft building up a static charge in the first place (that's what those little wires, known as wicks, sticking out the back of the wings on some aircraft are for). When you're in a boat it would be worth making sure your rig doesn't have a significantly different charge to the sea your in but I would have thought that unlikely anyway. Your best bet would be to make sure the the full effect of the strike doesn't go through anything critical.

As much as opinion as hard fact though - it's still an area where there's some consensus but many credible dissenters.
 
The area around the Straits is a bit prone to thunderstorms.

Thursday last week, there was a very large strike on the runway next to Marina Bay Pier1 that blew a hole in the tarmac! It was also raining.

This was of great interest to:

The Marina Staff, who were wetly docking a 30 odd metre motor boat and stood nearby.

My wife who hates lightning and was returning on a Tourist boat from a bay excursion, calming the passengers.

The pilot and crew of a small business jet waiting to take off just a few yards further along the runway..... they had to return to the terminal.

I could see it strike from about 10 miles away! Spooky.
 
>A 'lightning conductor' is surely just that. A heavy copper ribbon designed to conduct lightning away from or past the building it is there to protect, in the event of a strike.

That's what's I thought. Our university hall of residence had a massive copper strap over the sides and top of the building. I have no idea if it would work in a strike. However if you pushed an HF radio aerial wire in the the earth hole of a plug it gave a fantastic worldwide reception. A handy tip I think ;-)
 
If it was the sort of thickness Seajet described then it stands a chance but the flat copper strips you usually see (about 1" x 1/8" at best) are really just bonding strips. They often vapourise long before the full charge has dissipated from the strike - I've seen the chunks of concrete blown from a building that had one of those fitted - most of the copper had simply gone. It's one of the things that made me dig a bit deeper into the subject.
 
grumpy_o_g said:
If it was the sort of thickness Seajet described then it stands a chance but the flat copper strips you usually see (about 1" x 1/8" at best) are really just bonding strips. They often vapourise long before the full charge has dissipated from the strike - I've seen the chunks of concrete blown from a building that had one of those fitted - most of the copper had simply gone. It's one of the things that made me dig a bit deeper into the subject.
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We had one of these strips down the side of my old Junior school. It was a moudly green colour covered with dirt and moss and oxide. One day there was a big bang overhead and the school shook. When we went outside at playtime the strip was beautiful gleaming pink copper. It seemed to do the trick as there was no damage.

On the other hand, a lightning strike (or discharge at least) here at home last week destroyed my aerial booster in the loft! Spend £20 yesterday at Maplin getting another.

Richard
 
I was working on my car in the garage years back and the garages were in a block in a separate area behind the houses. Lightning struck a friends bungalow about 50 feet directly behind my garage, knocking a hole in the roof and taking out his nice new TV and a few other things. I was one second standing in the garage and the next laying on the ground outside the garage, unhurt but slightly 'shocked'.:) Strong smell of ozone too.
 
lightening

We were struck in the aftremath of hurricane Alberta in the gulf stream.
A fifty-foot steel ketch. Large secion al mast about 60 ft high.
A ball of spikey flashes about 20 feet across at the mainmasthead lasted for about 5 seconds during which i felt as if I were being lifted off the deck, and then there was a violent flash and I was knocked down onto the deck
Down below, nobody was hurt though they saw flashes running along certain wires.
Most electric cabling had melted. An interesting feature is that where cabling went round a rt angle bend the insulation had been blown off in the direction of flow of the current. I was later told that this was due to plasma effect.
Some remarkable things.
Both the Deecca radar and the VHF went on working. Both these were mounted on the mizzen.
But our biggest problem was that the flash was folowed a few mins later by a short sharp whirlwind which ripped all the sails out of their gaskets and reduced them to shreds and rolled the boat over 360 degrees.
Throughout the hurricane we had logged the direction of the swell and the compass was noted as being 120 degrees out. We had only the swell to guide us.
We had spare sails below and set them and sailed towards Newport and the US coastguard aircraft which found us, flew over us on a true north heading.
This was the third strike at sea that I have had. The other two were in the Indian Ocean.
I do not think there are any meaningful precautions you can take against strike damage except to have a steel boat, so that then one is in a Faraday's box and comparatively safe. The only damage we had was to the wiring probably by induced currents. The masts ans standing rigging did not suffer at all.
On arrival at Newport R.I. we cabled GJW with the basic facts.
They replied simply "get it fixed."
You know, things happen at sea, and mostly, when they do, it's not as bad as you feared.
 
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