Conducting Lightning

[3reefs]

I've no idea if this is sensible or very foolish - standing by to be told!

If I do nothing and my boat is hit by lightning, anything could happen, including sinking when the flash decides to exit through one of my hull fittings.

I carry some jump leads so that I could use all batteries for engine starting.

If I clip my jump leads onto shroud or backstay and leave the other ends in the sea, am I making it more likely that my boat will be struck?

Also if the mast is hit, will the "fickle flash" like the route prepared, or will it be like my teenagers, and just do what it wants anyway?

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[oldharry]

Look up the archives - there's loads on this issue been debated. But the answer is basically no one seems really to know for certain.

Lightning will do its own thing anyway, but like you, I hope that it will go away if I hang something over the side to give it a direct path....

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[johnsomerhausen]

If you have a deck stepped mast and a bolted on keel, then the solution recommended by a chap at the University of Florida (which has the highest inccidence of thunderstorms in the USA) is fastening a battery cable from the mast footplate to a keel bolt (the one closest to the vertical from the mast). That should give you a good conductor for the lightning dischargce. If you don't have a bolted-on keel, he recomends expoxying a one square foot copper plate to the bottom, with a bronze (not brass) bolt going through it and the hull to which you fasten the battery cable.
john

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[ccscott49]

It seems from past experience and first hand knowledge, the lightning will doo it's own thing and fry all your electronics in the process, but a cable from mast to keel bolt or cable over the side might help, who knows?

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[Moose]

As long as there are enough yachts around this doesn't affect me!!!/forums/images/icons/laugh.gif

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Moose

 

[Peppermint]

Re: I\'ve just disconected by shroud to keel strap.

It appeared to be generating a little current.

Having discussed the subject with a couple of electricians and a girl I know with an aptitude for hard sums I came to the following conclusions.

Always moor near bigger boats with tall masts.

Your idea for earthing external to the hull is preferable to encouraging the charge into the boat. Keep it outside if possible like Farraday's cage.

If your struck it will fry your electrics no matter what. It's the price we pay for sticking wires up to the masthead.

It's a lottery.

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[wayneA]

The Website with all the info from Uni of Florida can be found at

<A target="_blank" HREF=http://www.thomson.ece.ufl.edu/lightning/>http://www.thomson.ece.ufl.edu/lightning/</A>

<hr width=100% size=1><font size=1>Experience is something you don't get until just after you need it.</font size=1>

 

[vyv_cox]

Great how these discussions go around and around!

My two-penn'orth. Lightning strikes are anything between 1 and 5 km in length. The power of a strike is awesome. The gap between your mast and keel is about 2 metres. Does anyone believe that a lightning strike will be influenced in the slightest by a 2 metre length of wire?

There does seem to be some practical measurement support that an insulated, non-earthed mast tends to attract less strikes than an earthed one. I wouldn't put money on it myself.

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[oldharry]

No, Vyv, I dont think it will (make the slightest difference, that is), but it makes me feel better having done something which might just cause the step leader to take a slightly easier path before the main discharge follows it.

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[vyv_cox]

But if the mast is not earthed to the water, maybe the leader would not strike upwards in the first place? Don't ask me, I only read the available information like most of the rest of us.

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[gunnarsilins]

Connecting mast to keel

In case the mast is connected to the bolted-on keel as suggested you should be aware of potential problems with galvanic corrosion.
One solution is to break the path between mast and keel with a very small gap (lets say a mm or so) This gap will easely be jumped over by the lightning but no galvanic current will flow.
Such an gap can easely be made with a small plastic box with two bolts mounted from opposite directions, leaving about a millimetre between them. The cables can easely be fastened on these bolts.

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[oldharry]

Re: Connecting mast to keel

Like Vyv, I only have opinions based on what i have read (mainly on these boards) about it. The 'feel a bit better having done something' factor is admittedly very marginal. Having lightning around when sitting near the base of a large metal spike scares the willies out of me.....

However the thing that worries me about having an in hull grounding plate is what happens to it if the boat IS struck. There are many accounts of transducers and other through hull metal bits being blown clean out, with obvious disasterous results. I cant help wondering whether putting a large metal plate in the hull is not asking to have a large hole blown through it? Even if the plate survives, the heat would surely flash out the supporting resin in the GRP, thus making the boat sink that much quicker?

It seems to me to be a no-win situation.

And yes, Vyv, arguably, stopping the leader forming in the first place is a better option, and is probably better acheived at the mast head with proprietary gadgets. But as it is usually raining anyway, the mast will already be connected electrically to ground , so my - probably forlorn - hope is that I can provide a lightning conductor: an easier path to ground outside the hull without punching holes in it: where the leader goes the main charge might just follow. But then again it might not....

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[Guest]

Post deleted by danfoley

 

[gunnarsilins]

Do you empty....

...the contents of you Tupperware containers into one of the small holes with caps on your batteries, or do you dip the batteries in the containers when charging them?



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