Lightning: things to do that limit damage

A Tv programme on lightning a few yeas ago had tested various American lightning protection devices, and found some of them actually increased the likelihood of a strike!

I agree with marsupial - no strike / strike, no damage / strike with extensive damage is up to the deities you have aboard at the time! Afloat there's not really anything you can do to stop 30million volts charging through your boat. Rubber plugs on the sockets to 'stop it jumping' is just wishful thinking. That stuff can blast straight through a GRP hull. Lightning likes to travel in a straight line, and if for example the main discharge travels down a keel stepped mast, it blows a hole straight through the bottom of the boat, even if there is a heavy jumper cable diverting it to an earthing plate. One of the main causes of sinking after a strike is through hull transducers being vaporised.

Sad story: the bloke who took delivery of his brand new Westerley, and on the way home across Lyme Bay was struck by lightning, burned out and sank! To make things worse, his Insurance wanted to up his premium on the replacement because he had a claim. He took his business elsewhere.
 
>The best defence is a steel hulled boat.

That may be the case if the lightning hit the hull but it always hits the highest thing, the mast, and the same damage will be caused. An example is an Australian boat that was hit by lightning, when he talked about it he said the worst thing was he kept beer cans in the bilges and they were all welded together. Which shows he had his priorities right ;-)
 
When I asked about this before on this forum, there was a similar variety of answers and opinions reflecting, I think, the variety of different experiences, and varying quantities of damage done.

What a steel hull does prevent is the pepper-pot holes blown in the bottom of a GRP hull, but these don't always happen. A wooden hull - but it's more of an issue to wet spars - can be turned in short order into a bunch of matchsticks. As has been said, rhyme and reason seem hard to come by with lightning strikes...
 
Been struck twice! (Stay away from us in an anchorage!) Been anchored next to boats that have been struck at least half a dozen times..........(In the Tropics).

Only equipment that survived was the stuff that we put in the oven( TAYLORS-GLASS DOOR). Laptop,Handheld VHF,GPS. Lost the ssb even though unplugged, VHF aerial,autopilots etc.

No rigging damage though and no holes.

Have seen two catamarans sink after a strike- both had thousands of pin holes along the waterline. Generally the cats suffered far more residual damage too.

Moral, don't rely on electronics! Be wary of modern engines that have electronic control systems, carry spare lights. Don't sail in the Tropics!
 
A Faraday Cage absolutely will protect against an EM pulse. It will not protect against a steady magnetic field (compasses work inside a Faraday Cage) but it is used throughout industry and in the military specifically to harden electronics against EM pulse damage. An EM pulse, by definition, isn't a steady field.

Faraday cages don't have to be 100% enclosures of a conducting material to work though gaps will reduce the efficiency. The design of Faraday Cages can be quite complex but a steel oven, even with a glass door, will be much, much better than nothing. Put the VHF, GPS, whatever in a biscuit tin and put that in the oven if you are in a seriously high risk area. Dont forget to make sure the gas is off at the bottle too. If the oven (or anything other than a specially designed Faraday Cage) takes a direct hit from lightning the current will probably vaporise it anyway - the idea is really to protect more sensitive kit from stray currents and the EM pulse.

It's still not fully understood but there is a school of thought that says bonding the mast to the keel basically ensures the mast is at the potential of the sea instead of the atmosphere so may encourage a strike rather than protect against it. Strictly a theory though and there's no clear data on it either way.

If the strike does happen to hit the mast and you've got said copper cables in place to the keel it is now more likely to carry the full current of the lightning strike rather than ionising the air around it - effectively your mast and, big problem, your keel is now part of the lightning conductor - definitely bad. As per William_H, run the cables direct to the water over the side. You may lose the mast but at least you've got a hull to sit in.

Old Harry - has the measure. It's effects are down to luck as far as we are concerned until we understand lightning better. Lightning does seem to prefer straight lines. It definitely doesn't always hit the tallest object though it is more likely.
 
There's a lot spoken about lightning strikes but how much of it is true I'm not certain.

I refer honourable members to my post 3 where speaks someone with apparent knowledge.
 
Marsupial said:
my experience of lightning strikes is that there is very little you can do to prevent damage to anything electrical. I have seen boats directly hit where no damage has occurred, others that have been directly hit where everything has fried including battery powered devices with no batteries in them and rigging joints, and more where the strike was many tens of metres away but everything has fried. I have seen fork lightning hit the sea a few metres from my boat (Ionian Sea 2010) and we suffered no damage; so there is no rhyme or reason to this stuff.

Mrs thinks the best defence is an array of deities lined up on a shelf in the saloon and lots of prayer.
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I couldn't agree more. I do take the threat of lightning strike seriously though as I have seen lightning strike the ground 50 meters away, my TV aerial was zapped (I'm right on the ocean) and one neighbor had his lobster boat zapped and the other his factory building.

I used to envy people who had cruised up the Amazon but not anymore. Manaus seems to have a thunderstorm everyday AND boats in freshwater suffer more damage than boats in sea water. Have a look at this (it does appear when you are well out to sea it's pretty safe).

http://geology.com/articles/lightning-map.shtml

http://www.youtube.com/watch?v=iJ88efj8Jno
 
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coopec said:
I couldn't agree more. I do take the threat of lightning strike seriously though as I have seen lightning strike the ground 50 meters away, my TV aerial was zapped (I'm right on the ocean) and one neighbor had his lobster boat zapped and the other his factory building.

I used to envy people who had cruised up the Amazon but not anymore. Manaus seems to have a thunderstorm everyday AND boats in freshwater suffer more damage than boats in sea water. Have a look at this (it does appear when you are well out to sea it's pretty safe).

http://geology.com/articles/lightning-map.shtml

http://www.youtube.com/watch?v=iJ88efj8Jno
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I've had lightning hitting the water about 50 metres away - several times - then hit a ship nearby, in the English Channel; to use a technical term we were frightened fartless ( " It's just a matter of time isn't it ?! " ) and blew up the dinghy, trailing it behind as Plan B - obviously we got away with it or I wouldn't be typing this.

On another occasion, at my club a 20' wooden yawl was hit on her short wooden main mast, blowing a plank out of her side; the bigger boats with much taller alloy masts were untouched.:rolleyes:
 
grumpy_o_g said:
The design of Faraday Cages can be quite complex but a steel oven, even with a glass door, will be much, much better than nothing. Put the VHF, GPS, whatever in a biscuit tin and put that in the oven if you are in a seriously high risk area.

It's still not fully understood but there is a school of thought that says bonding the mast to the keel basically ensures the mast is at the potential of the sea instead of the atmosphere so may encourage a strike rather than protect against it. Strictly a theory though and there's no clear data on it either way.

If the strike does happen to hit the mast and you've got said copper cables in place to the keel it is now more likely to carry the full current of the lightning strike rather than ionising the air around it - effectively your mast and, big problem, your keel is now part of the lightning conductor - definitely bad. As per William_H, run the cables direct to the water over the side. You may lose the mast but at least you've got a hull to sit in.

Old Harry - has the measure. It's effects are down to luck as far as we are concerned until we understand lightning better. Lightning does seem to prefer straight lines. It definitely doesn't always hit the tallest object though it is more likely.
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What's said above is much the same as I was told by a professor of something or other. If earthing the mast then a dissipator has to be fitted or it would be more likely to attract strikes. Evidently sharp pointed lightning conductors and dissipators are there to reduce the chance of a strike rather than conduct it. Disconnecting aerials won't do any good in a direct strike, a 12" gap from a hanging wire isn't much of a problem for a million or two volts to jump but he felt that the oven would help protect things from stray fields from close strikes.

There doesn't seem to be any rule about where lightening will or won't strike, I've seen strikes to sea between moored boats and on to the salt marshes but no boats hit - must admit my bum was twitching! We also had a buzz one time crossing Biscay where the instruments went crazy for a while and then recovered, without any strike seen. Very difficult to keep away from metal on a boat with chainplates behind seating, stays at the end of bunks and masts down the middle with associated cables running everywhere.

Reading one post above made me smile, I well remember the Joburg summer cu nims, could almost set your watch by them in an afternoon.
 
I have read that it is not uncommon for ships to be struck. Apparently it does not affect them. With aircraft is a different matter though. It is not so much the lightning strike but the enormous down drafts associated with thunderstorms. It is an absolute NO, No for an aircraft to fly into these downdrafts but sometimes pilots can't see them at night (no moon) and normal radar doesn't pick them up. So we all just trust to luck we don't hit one. They have developed a very sophisticated radar ("with all sorts of algorithms") but only the latest aircraft have them.
 
coopec said:
It is an absolute NO, No for an aircraft to fly into these downdrafts but sometimes pilots can't see them at night (no moon) and normal radar doesn't pick them up. So we all just trust to luck we don't hit one. They have developed a very sophisticated radar ("with all sorts of algorithms") but only the latest aircraft have them.
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Can't always be avoided, I've been on a commercial flight over the Brazilian rain forest where pilot had to slow down to keep within the operating envelope, it was so turbulent. First time I saw St Elmo's.
 
coopec said:
I have read that it is not uncommon for ships to be struck. Apparently it does not affect them. With aircraft is a different matter though. It is not so much the lightning strike but the enormous down drafts associated with thunderstorms. It is an absolute NO, No for an aircraft to fly into these downdrafts but sometimes pilots can't see them at night (no moon) and normal radar doesn't pick them up. So we all just trust to luck we don't hit one. They have developed a very sophisticated radar ("with all sorts of algorithms") but only the latest aircraft have them.
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Some aircraft get away with ligntning strikes, some don't; I was called to photograph a couple of Harrier GR5's at Wittering which been hit by lightning, there were tracking marks from the fuslelage spine to the wingtip and all electrics were lost, quite a big deal on a Harrer II but both recovered safely- a testament to 1 Squadron.

I always thought the high graphite content of the carbon fibre wing - at the time the GR5 wing was the largest man made carbon fibre structure - made it attractive to lightning, ( I dearly hope the carbon fibre gearknobs used by Halfords fans with back to front baseball caps have a similar attraction ! :rolleyes: ) but then I used to dangle a chain over the side of my boat as a conductor; now I l don't as the jury is out as to whether I'm making the boat attract lightning or not !
 
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Civilian transport aircraft are tested to resist damage from Lightning strike. They are actual struck quite often. Flying through clouds they are susceptible to the cloud to cloud lightning. I have been involved in the inspection of a transport jet after lightning strike. You could identify where the lightning entered and where it exited the fuselage nose to tail by tiny burn marks. The inspection involved checking the compass for deviation and of course check all electronics. In this case no problems. Carbon fibre needs special protection because it is a conductor but not a good one. So like a tree if hit it will explode in heat. Wire mesh is often layed on the surface to reduce ressitance. On fibreglass radomes on aircraft they fit longitudinal ali strips on outside or inside to provide a low resistance conductor. The nose is a bit like an ali mast. Gives the pilot a fright and bright flash of light. They have what is called storm lights in the cockpit. A single switch turns all instrument lighting to full brightness because he loses night vision. (to say the least.

If we consider the lightning protection that has been provided on church spires for a very long time we have to assume that it is a successful protection. Usually copper strap about 50mm by 4mm from the top down to the ground. often duplicated. So i would reckon that that is the sort of conductor you need ali mast to water or to keel. Provided it is a good low resistance connection to the keel. Every point of resistance will get very hot.So not just one ss bolt but several as connection point.

Regarding the so called dissipators. Very fine points of a conductor tend to concentrate the electrostatic field from high voltage. This concentration means that you get a discharge at lower voltage or less energy build up. So it dissipates by discharging earlier. hence a church spire will have pointy rods as highest point. So yes there could be advantage in having sharpened points on mast top. This does not have to be low resistance but if it has resistance it will melt with the lightning strike. But it will have done its job by then. Aircraft fit little spikes or brushes on thetrailing edge of wings and tail. These tend to dissipate at lower energy static build up which can cause radio interference. So I am told. or are they to deter ligtning strike? All very interesting and a science so had to quantify. good luck
 
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I agree with the advice about steel yachts. They probably encourage strikes but they are quite safe inside and unlikely to have a hole blown in the hull by the discharge. People say that if you have cables leading from the outside to the inside that will ruin the "Faraday Cage" protection of a steel hull, but that has not been my experience.

I've only been struck once on my steel yacht, in Florida. I had disconnected all aerials but everything outside was fried including radar, gps aerial, vhf aerial, fluxgate autopilot compass, mast-head light. There was a stripe about 10cm wide down the port side of the boat from the cap shroud to the bottom of the keel where the paint had completely vanished leaving bare metal. Curiously for a long while that area would not accept paint: if applied it quickly came off again. Cables (inside mast etc) were little damaged and all the kit inside was fine. The main steering compass survived but with a 40 degree deviation.

On a quite separate occasion I had really spectacular St Elmo's fire. This was in a severe night-time thunderstorm off NW Africa when the air was exceptionally humid. For an hour the lightning discharges were virtually continuous for minutes at a time, the light was so intense that it hurt my eyes. During the dark gaps there was visible a great flame of light from the masthead, and violet fluorescent balls of light at the shroud tips. Some people report a crackling discharge with St Elmo's fire, but it seemed to me quite silent, at least in relation to the general noise of the thunderstorm.

I don't like thunderstorms at sea, they are more scary than gales. But its very rare for a yacht to be fatally damaged by a lightning strike, and perhaps irrational to be over worried by them.
 
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William_H said:
If we consider the lightning protection that has been provided on church spires for a very long time we have to assume that it is a successful protection. Usually copper strap about 50mm by 4mm from the top down to the ground. often duplicated. So i would reckon that that is the sort of conductor you need ali mast to water or to keel. Provided it is a good low resistance connection to the keel. Every point of resistance will get very hot.So not just one ss bolt but several as connection point.

Rgood luck
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I plan to concentrate on lightning protection now that I have my instruments sorted out and wanted to upload a photo of what bits and pieces I have and run it past you guys but YBW thinks I exceeded my photo limit so that will have to wait.

When I got Taskers to do my mast I told them I wanted lightning protection. When I got them back I found there is a heavy co-axial cable going right to the top of the mast. TWO QUESTIONS Is that for lightning? AND Surely the aluminum mast would have been adequate to conduct the charge?

(I've got a lot of other "things" I want to sort out but they will be the subject of another post when I can upload a photo)

Regarding turbulence and aircraft:
"In general, the risk posed by thunderstorms is from the convective motion of the air within them, the powerful updrafts and downdrafts that can push a plane around, potentially damaging it or worse. (These drafts are one of the stronger forms of turbulence.) "
 
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Are lightening strikes a major form of premature death? Should I be worried? What are the risks if I upgrade my boat to an aluminium one? Should I buy a plastic sextant? Will my lifejacket inflate?
 
There is a device like a metalic bottle brush, you can put this on the top of your mast and connect to ground (water) via a cable. The idea is that this will slowly bleed the negative ions from the local area as these are attracted to the metalic points on the brush, this will give an inert area around the brush so lightning will not see it as a convenient path to earth. I had a lighting strike on my Kingfisher some years ago, the only damage was a small hole in the wind indicator at the top of the mast. Only noticed it when I took the mast down.
 
coopec said:
I plan to concentrate on lightning protection now that I have my instruments sorted out and wanted to upload a photo of what bits and pieces I have and run it past you guys but YBW thinks I exceeded my photo limit so that will have to wait.

When I got Taskers to do my mast I told them I wanted lightning protection. When I got them back I found there is a heavy co-axial cable going right to the top of the mast. TWO QUESTIONS Is that for lightning? AND Surely the aluminum mast would have been adequate to conduct the charge?

(I've got a lot of other "things" I want to sort out but they will be the subject of another post when I can upload a photo)

Regarding turbulence and aircraft:
"In general, the risk posed by thunderstorms is from the convective motion of the air within them, the powerful updrafts and downdrafts that can push a plane around, potentially damaging it or worse. (These drafts are one of the stronger forms of turbulence.) "
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Almost certainly they have fitted the coaxial cable for the VHF com antenna. The heavy cable is RG8 having much lower losses than the more common RG58u and so better for a longer cable run. Also of course the heavier cabl;e will be more robust against corrosion etc. My guess being that they did not know what you wanted or what to do for lightning protection. good luck olewill
 
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