Faraday cage

Thomasina

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Hi All.
I want to protect my spare electronic equipment (GPS and laptop) in the event of a lightning strike on the boat. I am told the Cooker makes a good Faraday cage, but would rather have a cage where the items could be stored full time. Any thoughts on self building one would be appreciated.
Thanks.
Norman Brett
 
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Assuming you'd left the EPIRB in a Faraday cage presumably?
 

Steve Clayton

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From what I've read about lightning strikes to boats then I would expect all instruments electrically connected to the boat's power system to be taken out. Those items isolated from the boat's electrical system should be OK. Not been in that situation personally so maybe someone who has would be prepared to comment.

I doubt whether a Faraday type cage (chicken wire or similar) and it's contents would withstand the effect of a lightening strike but it's an interesting hypothesis
 
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If that were true it would also apply to handheld GPS's, computers etc., in which case a Faraday cage wouldn't be necessary for any electrical items. Fixed electrical items could be protected just by disconnecting them from the ship's supply.

My (extremely limited, based on foggy memory of reading accounts in the yachting mags) understanding was that in a lightning strike there is so much current pumping around the boat that one would be lucky if any electrical items survived (unless suitably caged).

Wouldn't it be a good thing rather than a bad thing if one had an alternative to reliance on an EPIRB for sending a Mayday ie. the alternative of being able to carry on one's journey without being rescued?
 

BobOwen

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Did anyone see the program on the box a year or two ago re: lightning? If I remember right, it was carried out in a workshop in Germany somewhere, ( Siemens test lab ?).

Seems the safest place in a lightning storm is in a vehicle - fuel being irrelevant.
To test the theory they drove a small car with a guy inside, beneath these almighty voltage generator Van de Graff things.

They then zapped it with mega volts and caused huge lightning bolts to repeatedly zap the car roof, from a device held about 2 metres above. The guy - complete with electronic live radio camera - commented on it while being zapped.

He felt nothing - not even sticky up hair. When the test was finished, the car started up and drove away. All the electronics and electrical controls still working.

Been a serious believer in Faraday cages since! /forums/images/graemlins/shocked.gif
 

boatmike

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I think I would want to be inside the cage with them. The most important thing to survive a strike is me! Seriously though there are more problematic effects of a lightning strike, like blowing transducers out of the hull and sinking. I am no expert but would unplug all arials if I thought there was a danger of a hit and try to rig a lightning conductor from the mast over the side into the water. Perhaps a length of chain?
Dunno.... but I think a lightning conductor is a more comprehensive protection than a biscuit tin....
 

Steve Clayton

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[ QUOTE ]
Wouldn't it be a good thing rather than a bad thing if one had an alternative to reliance on an EPIRB for sending a Mayday ie. the alternative of being able to carry on one's journey without being rescued?

[/ QUOTE ]

Not quite sure I understand what the above is saying but if the boat appears seaworthy then I could carry on and make towards the nearest safe haven without electronics.

As I said it's all a case of risk and how you assess it:

Likelihood of lightening strike; very low; impact high but who carries a Faraday cage?

Similar risk parameters:

Likelihood of having to evacuate a boat; very low; impact; high (you loose lives) so to mitigate that specific risk we carry liferafts.

No doubt some chandlery supplier will read this and we'll see boat faraday cages on the market in a couple of months!
 
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I seem to remember that the last thing I read on the subject advised that the use of conductors like trailing metal objects overboard was not advised. I'm not sure why - I had the impression that it may have been that it decreases the resistance of the boat, making a strike more likely - electricity takes the easiest route to earth and all that, and that the amount of power involved in a strike was more than any normal conductor might be able to cope with so wouldn't help much?

But maybe I got that wrong. Any experts out there?
 
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Well yes, I would hope that it wouldn't be a Mayday situation. It's just you said you would consider setting off the EPIRB, so I was responding to that.

My point was that having a handheld GPS still in working order would be better than not having one. In practise I guess it would only work if it were always kept in a Faraday cage. That's not too difficult to arrange: the handheld needs to have somewhere it is normally kept on board, and why not in a biscuit tin or equivalent?

Keeping a handbearing compass in a similar arrangement (perhaps separately as the GPS's batteries may not do it any good) might not be a bad idea. It's unlikely the ship's compass will still be showing the right way to America after a strike.
 

Sea Devil

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Re: Faraday cage - biscuit tin

Although lightning hits on boats are fairly rare this side of the Atlantic for some reason they are very frequent on the other side - I took a hit in the Potomac river that cost my insurers a lot (YM article on my web site) wiped out everything - fridge SSB domestic world radio on the table - some wiring....

After that I kept a spare HH GPS in a biscuit tin in the bows.. compass was 20degrees out!

Met several boats that took strikes out at sea - makes dr really difficult if you do not know your compass error - and you don't!
 
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Re: Faraday cage - biscuit tin

Your article makes interesting reading. Any reason why you keep the biscuit tin in the bows?
 

PilotWolf

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Re: Faraday cage - biscuit tin

Seem to remember a device being available that looked like one of those 'alien fibre optic lamps' that was fitted at the highest point to deter lightning strikes.

Aeroplanes are a flying farady cage but the damage to electrics and nav equipment can be amazing...

PW
 
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Re: Faraday cage - biscuit tin

Does the fact that a plane isn't touching the ground ie. isn't earthed, make a difference?
 

PilotWolf

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Re: Faraday cage - biscuit tin

Don't think so - if you ever see a video of a strike (on aircraft) slowed down you can see the strike flowing over the outside of the aircraft skin.

PW
 
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Re: Faraday cage - biscuit tin

OK, another theory then: an aircraft has all kinds of aerials sticking through the outer skin, and one might reasonably the voltages concerned to be unhealthy for sensitive electrics connected to said aerials.

Most biscuit tins, on the other hand, don't have aerials.
 
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