Lightening protection

[temptress]

So last night we sailed through a very large thunder storm with Lightening all around. We did our usual odd disconnecting the vhf, turning off electronics and putting some essential stuff in the oven.


It lasted an unusually long time and I was thinking there must be a way to rig up some effective protection and weather putting stuff in the oven a actually works.

What have others done?

 

[macd]

Putting electronics in a Faraday cage such as an oven certainly protects them, providing you don't turn it on. The hull of a steel or aluminium boat, of course, is essentially a very big Faraday cage.

There's a lot of disagreement on the overall issue of lightning protection between people far better informed than me, and plenty of previous threads on the subject: worth a search. The debate seems to centre around two opposite strategies: giving lightning a clear path to ground, which some suggest encourage strikes; or the opposite, which may deter them but lead to greater damage should strikes occur. Some boats, especially in the tropics where you are, have hard-wired paths to ground; you hear of others who have the equivalent of jump leads, one end of which is fastened to shrouds and the other dumped in the oggin. Whether skin fittings are bonded (as is usual in the US), or not (as in Europe) can also have some bearing.

The immediate threat to people on board is evidently slight, providing they stay clear of conductors (rigging, etc). If you have a copy of Calder, you'll see reference to a 'cone of protection' offered by (conductive) masts, which would normally enclose the whole boat. Secondary effects, such as blown-out skin fittings, fried engine electrics, are another matter.

Tip: the search will work better if you spell it 'lightning'.

Another thought: lightning is very much more of an issue in the US than much of Europe. It might be worth trawling through a US forum or two on the subject, or even posting your question there.

P.S. To anyone who might be worried about imminent strikes, there is currently only one area of lightning activity in the whole of Europe, and that's just north of the Crimea: http://en.blitzortung.org/live_lightning_maps.php?map=10
Really useful site.

 

[Salty John]

Yes, what macd said.
Just to add that the ABYC devotes a whole standard to lightning protection - Standard E-4. It's the advice I'd follow. I would not include seacocks in the bonding, but then I'd have Marelon seacocks anyway.

 

[Halo]

I seem to spend a lot of time sailing past wind farms. I have thought that if I get in a lightning storm I will dive in there and be surrounded by lightning rods. What do people think?

 

[macd]

Just to add that the ABYC devotes a whole standard to lightning protection - Standard E-4. It's the advice I'd follow. I would not include seacocks in the bonding, but then I'd have Marelon seacocks anyway.

Thanks for the info, Salty John. It seems it's now Standard TE-4, which can be downloaded from ABYC for a not very enticing $50.
No doubt a more diligent search could unearth it (no pun intended) for nothing, but in the meantime there's a precis here:
http://www.kp44.org/LightningProtectionABYC_Standards.php

And here's an interesting article on an alternative approach: http://www.yachtingmagazine.com/fire-sky

 

[temptress]

Interesting. I have a copy of Nigel Calder s book and thus is what started. Me thinking. I have been in a good few storms and not had a hit but you never know. I'm not sure the. old 'put it in the oven' eve works. As we head up to Singapore next month it is on my mind. SG has the third highest level of lightning activity in the world.... The other 2 places being inland in South America some where and at altitude....

 

[macd]

I'm not sure the. old 'put it in the oven' eve works.

If you believe Faraday cages don't work, you'd have to be pretty reckless to get in a commercial aeroplane.

That said, putting, say, a VHF in the oven might protect the set, but not its cabling and aerial, so the result might be the same as if you hadn't bothered. All the more reason then, for popping your hand-held in the oven...and its charger. And your EPIRB. But maybe best to choose an oven without a glass door.

 

[vyv_cox]

A neighbouring boat a couple of weeks ago had been struck by lightning some years previously. Every electrical item on board was destroyed - alternator, starter motor, wiring and of course all electronics. Total repair bill was €30,000.

 

[macd]

Wasn't a Rassy parked at the time in Levkas, by any chance, Vyv?

 

[rogerthebodger]

Interesting. I have a copy of Nigel Calder s book and thus is what started. Me thinking. I have been in a good few storms and not had a hit but you never know. I'm not sure the. old 'put it in the oven' eve works. As we head up to Singapore next month it is on my mind. SG has the third highest level of lightning activity in the world.... The other 2 places being inland in South America some where and at altitude....

Living in an area of high lightening activity I have lost several electronic devices mainly at home not on the boat.

If you get a direct strike not a lot will protect your boat. Having had a direct strike on my eathed TV antenna not even the 10mm earth wire could be found.

The most damage I have had is the electromagnetically induces current in any wiring that will take out most electric equipment. This is where a faraday cage can help. I have a steel hull and that is suposed to act as a faraday cage but some have reported that lighting can still damage electronics inside a steel boat.

Lighting protection is not simple. I used have a bank of modems that were taken out regularly until I doubled up on the mains and incoming data line protection.

You pays your money and takes your choice.

This is the kind of lighting protection I use at home.

http://www.clearline.co.za/product-catalogue

Temptress are you planning on coming our way on you way back to the UK. If so look me up.

 

[mjcoon]

If you believe Faraday cages don't work, you'd have to be pretty reckless to get in a commercial aeroplane.

There was an item on TV a few months ago about fuselages made of non-conductive composites. Apparently a very fine copper mesh could protect from lightning strikes at a small weight penalty. But that would have been protection from penetration rather than EMP.

Mike.

 

[JumbleDuck]

If you have a copy of Calder, you'll see reference to a 'cone of protection' offered by (conductive) masts, which would normally enclose the whole boat.

I'm afraid that Mr Calder is not a terribly reliable source on this, or indeed on many other things.

http://lightningsafety.com/nlsi_pls/cone-of-protection-myth.html

 

[JumbleDuck]

If you believe Faraday cages don't work, you'd have to be pretty reckless to get in a commercial aeroplane.

It depends what you think a Faraday Cage is, and what it does, and how. I've never been in a commercial aeroplane which was a Faraday Cage,

 

[JumbleDuck]

The most damage I have had is the electromagnetically induces current in any wiring that will take out most electric equipment. This is where a faraday cage can help.

Faraday Cages do not prevent inductive effects.

 

[duncan99210]

I have a feeling that most reasonably modern ovens have a glass door at the front, thus making them useless as faraday cage.

Having seen the damage to a friends HR after a strike, what struck me most of all was the scale of the damage caused to just about all the wiring on board. This was an a boat on the hard with just about everything switched off. The strike took out all of the electronics, most of the engine components (control panel, starter, alternator) and a fair number of the normal wiring circuits, like the lights. The path to earth for the strike was via the bonded skin fittings (the boat is an older one with an encapsulated keel): that took out all the bonding wiring as well as the skin fittings. Final contact with earth was made via two adjacent cast iron lamp posts, which simply disintegrated where the strike hit them. The amount of energy which must have been involved was amazing.

I have a feeling that there is not much that can be done to prevent a strike, nor is there a lot to be done to mitigate its effects. Perhaps making sure that the engine is running so if it's needed it's available is about the only thing that can be done?

 

[rogerthebodger]

Faraday Cages do not prevent inductive effects.

Thats interesting. This says differently

http://www.faradaycage.org/

I know that a faraday cage is used when testing an EPIRB to prevent the electromagnetic radio signal from escaping and triggering the EPIRB satellites.

 

[JumbleDuck]

he amount of energy which must have been involved was amazing.

Typically 5GJ in a single lightning bolt. For comparison, that's about 5,000 standard sticks of dynamite.

 

[TQA]

I had a 38 ft steel ketch which suffered a direct hit on the masthead. I was aboard down below at the time. masthead stuff was vaporized.

No apparent damage to the mast or rigging. About 50 % of devices with transistors or chips died including some stuff that was unplugged and sitting on a wooden table. So much for the Faraday cage effect!

An unexpected result of the strike was the hull becoming strongly magnetized rendering all deck level compasses useless.

 

[JumbleDuck]

I had a 38 ft steel ketch which suffered a direct hit on the masthead. I was aboard down below at the time. masthead stuff was vaporized.

No apparent damage to the mast or rigging. About 50 % of devices with transistors or chips died including some stuff that was unplugged and sitting on a wooden table. So much for the Faraday cage effect!

That's because your boat isn't a Faraday Cage and because Faraday Cage doesn't protect you anyway.

 

[Mark-1]

I think this is as close as anything I've found to a definitive source on this topic:

http://furledsails.com/article.php3?article=676

It certainly doesn't behave as I would think it would.