Lightening protection

[Seajet]

We were in St Helier marina one night during a pretty bad electrical storm - a Mirage 28 came alongside in the dark, no lights showing; as well as losing all electrics when she took a direct hit, the roller headsail foil had been melted too ( I forget the make but they were a resourceful couple, just back across Biscay - not sure if the forestay itself was damaged but the spare halliards also helped hold the mast up ).

Just to add to their fun, all the island's nav marks had been put out by the storm as well; this was before satnav.

We reckoned they'd earned a couple of stiff drinks.

 

[mjcoon]

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.

It's not difficult to design shielding to protect against a narrow range of frequencies. We expect our microwave ovens to do exactly that for us, including their usual glass doors.

But protecting against a huge pulse containing many frequencies is a different matter. Any metal object, even a hollow one, is likely to have multiple resonant frequencies and a pulse may stimulate oscillation at one or more, which will be detectable inside if hollow.

I note that the cited article misspells lightning too (with other typos), lessening my faith in its pronouncements...

However I did see a demonstration of a Faraday cage in the Deutsches Museum in Munich years ago when a chap sat in a mesh one while a massive discharge was applied to the outside. I don't suppose he was carrying a mobile phone though!

Mike.

 

[Jungle Jim]

The most impressive demonstration of a Faraday cage I ever saw was a demonstration in Boston (USA), at their science museum I believe. The demonstrator was inside the cage, like a giant parrots cage, complete with all his audio-visual control equipment. The cage was hoisted into the air and then hit with lightning pulses with him controlling the entire demonstration from inside the cage.

Regarding sticking stuff in the oven, I was taught by a very wise man to stick your portable electronics in a biscuit tin and bung that in the oven. Now that is a Faraday cage

 

[JumbleDuck]

The most impressive demonstration of a Faraday cage I ever saw was a demonstration in Boston (USA), at their science museum I believe. The demonstrator was inside the cage, like a giant parrots cage, complete with all his audio-visual control equipment. The cage was hoisted into the air and then hit with lightning pulses with him controlling the entire demonstration from inside the cage.

That's nice, and I have seen it myself (Strathclyde University, iirc, and the Deutches Museum, but it's not a Faraday Cage if you can see into it.

Explanation: a Faraday Cage is a closed conducting surface into the interior of which external electric fields do not penetrate. If there are holes then it's not a Faraday Cage. It may still be effective for lightning protection, because the bars of the cage or the mesh walls provide and low resistance alternative route for the current, but it's doesn't keep all electric fields out and it doesn't keep magnetic fields out, and these can, by induction, do all sorts of nasty things to nearby electronics.

Microwave ovens aren't Faraday Cages either: they demonstrate that (a) electromagnetic radiation does not significantly penetrate conducting materials and (b) EM radiation does not pass through holes in conducting surfaces if these holes are significantly smaller than the wavelength of the radiation. Microwave ovens use a wavelength of about 10cm, and the holes in the mesh are around 2mm diameter

 

[temptress]

Much my own thoughts. What I have been considering is how to be able to get to a safe harbour if all the electrics and even the compass gets messed up.

 

[rogerthebodger]

Much my own thoughts. What I have been considering is how to be able to get to a safe harbour if all the electrics and even the compass gets messed up.

Use the rising or setting sun.

 

[RichardS]

Explanation: a Faraday Cage is a closed conducting surface ......

Otherwise known as a boat oven. :encouragement:

Richard

 

[JumbleDuck]

Otherwise known as a boat oven.

As long as it doesn't have a glass door.

 

[RichardS]

As long as it doesn't have a glass door.

A boat oven with a glass door?

Is that how the other half live?

Richard

 

[macd]

Has anyone else been...er, struck, that during the last 24 hours we seem to have learned more about the nature of forums than we have about the OP's concerns?

Anyway, for anyone seriously concerned about lighning risk, the answer is simple. Just arrange to park you boat in here: http://www.nothingtoseehere.net/2008/09/the_faraday_memorial_london.html

 

[[70521]]

I am going to a lecture by a chap who does research on protecting aircraft from lightning strikes, I try and remember to ask him about boats.