Yachts and lightning strikes

cameronke

cameronke

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How vulnerable is a yacht in a lightning storm?

If my reasoning serves me right, charge concentration occurs at a point (for instance a yacht mast head ariel) and on a big open sea a single yacht would be an irresistable target.

What would happen? How regular are strikes?

Regards to all
Cameron

<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by cameronke on 11/05/2004 10:45 (server time).</FONT></P>
 
Found this info here

I have not knowledge of it wether it is all valid or not - as with everything on the net

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

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Lightning is one of the big FAQs on yachting forums. Do a search to check out previous threads on this site.

Yachts do occasionally get hit, though less often than you might think given the apparent vulnerability of the mast. Most reports come from Florida because of the concentration of yachts and the number of severe thunderstorms there. It rarely seems to result in death or the loss of a yacht, but almost always in serious damage to electronic gear and electrics generally, and localised scorching.

There are many theories about (i) how to repel lightning (ii) how to ground it safely if struck. For ever well-argued, convincing case that you can find on the internet, you will find another equally authoritative arguing the other way. There are a number of protection devices available of questionable efficacy - rarely seen in practice, certainly in the UK.

The one thing everyone agrees on is that if you are caught out in a severe thunderstorm it is advisable, if possible, for all crew to remain inside the cabin.
 
There is no one answer to your question but if you are out sailing in a thunderstorm, you are less likely to have a serious problem on a US built boat where Coastguard regulations require proper electrical bonding of all substantial metal parts of a non-metallic boat.

Yes, a yacht mast and its assocaited top fittings are usaully a good target for a lightning strike. However, like all electrical current, lightning seeks out the path of least resistance to ground (the sea). This could be, to quote an actual strike as an example, the wind transducer conductor and then then the instrument system wiring in hull to the depth sounder transducer. In the case I am thinking of the depth sounder was blown out of the hull and the boat sank (unoccupied on its river mooring). So to be really secure a yacht should have a "designed-in" low resistance path from the masthead to the keel. The keel, being of large area, should dissipate the energy into the water over its whole area, thus preventing "hot spots".

If you have a mast and rig that is not bonded to the sea, disconnecting masthead antennas and transducer cables would remove any highly conductive path which means the route for lightning from the base of the mast into the sea would have to be through the hull structure. As this is usaully a highly resistive path, the structure is likely to be damaged by severe instantaneous heating and could burn.

The only good news is that the risk to the crew is minimal (unless the boat sinks or burns of course) as metal rigging forms a "cone of protection", i.e faraday cage effect. Thus non-metallic stays and shrouds are not a dreadfully good idea.

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I heard that securing some metal chain from the mast to go over the side and into the oggin was a good idea in thunderstorms as it grounds the mast with very little risk to the boat or it's systems.

There's also the advice of having your compass checked after a lightning strike too.

<hr width=100% size=1>At the end of the day - Sunset.
 
Happened to the father of a colleague somewhere in the Caribbean. Essentially it fried everything electrical and electronic, including engine wiring loom and alternator. Quite a big insurance claim.

<hr width=100% size=1><A target="_blank" HREF=http://www.writeforweb.com/twister1>Let's Twist Again</A>
 
Have been told it's wise to place handheld VHF and GPS in the oven (off of course /forums/images/icons/wink.gif) in a thunderstorm since it acts like a Faraday cage and can preserve them in the event of a strike.

Tony C.

<hr width=100% size=1>There are 10 kinds of people, those who understand binary and those who don't.
 
Was it not an "act of God"/forums/images/icons/smile.gif

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Not sure I agree with all of this!

Firstly there is no way that the instrument wiring from the mast head transducer to the depth/log can carry enough current to blow the transducer out of the hull - the thin cables would vapourise instantly.

However in my unusually ill-informed opinion, bonding skin fittings could cause a problem. For similar reasons I would be hesitant of bonding the mast to the keel - having the keel blown off the boat can really ruin your day.

The advice of attaching a chain to the mast and hanging it over the side does seem to make sense in that it attempts to keep the current flow away from the internals of the hull.

Lightning doesn't actually have to strike the boat to sink or damage it. A lightning strike will induce a massive current in any electrical circuit in the vicinity - which is what fuses engine looms, destroys electronics and so on. For that reason it is a good idea to have a non-conductive break in the lifelines round the boat so that current is not induced in that.

I regard a lightning strike as pretty well the worst case scenario when sailing in that it can take out all the electronics (including VHF and EPIRB) and sink the boat at the same time

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Re: Steel boats

Answer is to buy a steel yacht,they are the safest in lightning.Sounds strange but the reason is that entire boat forms a Faraday cage .

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Lightning:
Almost nothing is known about how lightening behaves,
If there is lightening about it is likely that the whole exterior of the boat is wet,
Anything wet will conduct lightening to some extent,
The risk of being struck is incedibly low, how many thousands of miles have you and all your chums sailed, how many have been struck by lightening?

So risk analysis suggests, lightening is not a significant risk and there is little risk management worth employing.

All IMHO, of course.

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We were sat on our mooring one afternoon in Porthmadog. I was watching a thunderstorm approach from the sea, counting the lightning to thunder clap and realising it would be with us within minutes.

I was bothered not for our safety but the boat, I had only just re-launched her as she had been laid up for many years and we had invested everything into her. I am a pessimistic sod and decided that we were definitely going to get it.

I toyed with wrapping chain around a stay and hanging it into the water, but chose not to as I believed it might actually increase our chances of a hit. I did however remove all the mast connections except the wind instrument as it is uncut and requires feeding to the instrument at the helm, it would just have to take it’s chances.

Well up the river it came as predicted, fork lightning not 100m away. We went into the saloon, shut the doors and waited quietly, all power shut down at the battery switches. Then CRACK and everything went white, it was a little like how they portray a nuclear explosion in a film, I looked at Tanya and she was bathed in a white glow. The air was also odd, ionised probably.

Ok, so obviously we had been hit, as I predicted in my doom scenario, we watched the storm disappear off to the mountains that surround Porthmadog. I was the first to dare to venture out and see the carnage that must have been all around. Nothing, not a sign of anything untoward, maybe we hadn’t actually been hit after all.

The next weekend I was in the yard before going aboard Top Cat and met a chap working on his mast. I passed the time of day and he asked me about the storm the week previous. It turned out that his boat, three up from Top Cat on the trots had been hit, and he was clearing up the ruminants of a lightning hit. So three boats up and we thought we were the ones that got hit, being in the cabin if you are actually hit must be terrifying.

He damage included:-

VHF aerial gone – tiny scorch mark, but no aerial, no mounting bracket screws nothing, just gone.

All bulbs blown, even the tiny little ones in the engine panels, which he was most bothered about as they were around £20.00 each as sealed units.

His VHF which was plugged in at the time, stopped working. He removed the top cover and all looked fine apparently, but when he removed the bottom cover the unit was fried, (exit wound I expect).

From what I remember nothing else was damaged, his batteries, alternators etc. all appeared to be serviceable, I don’t know about long term damage. He was instructed immediately by his insurance to do the work and the pay out would be immediate. His insurance by the way were GJW.

Things I would do now in a similar situation were you have warning of impending storm…

1. I would not bother with a chain or try to earth the mast, I don’t think it makes a great deal of difference, lightning apparently travels upwards anyhow.

2. I would put all my electronics where possible into the oven, faraday cage effect, many yachtsmen have saved equipment in this way.

3. In hindsight, I forgot to shut the gas off, can you imagine?

4. I would always make sure no crew member was sat under the mast or near anything metallic, keeping away from wire runs may also be a good idea.

5. Just hope for the best!

I still don't to this day know if we had been hit by a finger of lightning that day, it really felt like it. There was no damage to the masthead, and no scorching noted when I unstepped earlier this year.


<hr width=100% size=1>J

<A target="_blank" HREF=http://www.topcatsail.co.uk>
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The chain trick certainly worked when my boat was charging up in a thunderstorm (buzzing noise, shocks from standing rigging, all electronics going down). Wrapping the anchor chain round the mast foot and shrouds and dropping a few metres into the water stopped all the symptoms while we motored like mad for somewhere safer.

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The cables, probably the screen, obviously did carry enough current before vapourising because how else did the echo-sounder transducer get blown out?

How do you connect your mast chain to an anodised mast to ensure good conductivity?

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Keep an eye out for the PBO October issue (maybe Nov) for an article written by some one who's "been there done that" (ie me). I was hit by lightning last year, it destroyed all my electronics, my fridge and my engine. But unlike some, I am still alive and still have a sailing boat
Richard Woods

<hr width=100% size=1>Woods Designs for quality sailing catamarans
www.sailingcatamarans.com
 
Without giving too much away how was your engine destroyed, are we talking the electrical side or was the engine as you say destroyed, I have never heard of that before.

<hr width=100% size=1>Julian

<A target="_blank" HREF=http://www.topcatsail.co.uk>
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Good point about the connection to an anodised mast.

Have never had to use the mast/chain thing, but I assume in a thunderstorm in a marine environment that there's enough salty water about to ensure a good connection.

The comment made above about the boat charging up in a storm, humming noises and static shocks from the rigging etc. was thought provoking. Saw this documentary about lightning, it explained how positive charges were generated from the ground, and eventually the negative charge from the cloud 'picked' one of several of the positive ionised trails to connect with. Sounds like that's what was happening with the boat, it was a positive trail waiting for a strike to hit it.


<hr width=100% size=1>At the end of the day - Sunset.
 
You may be right - I don't know the details of the case - but it is also possible that the damage was caused by an induced current. If lighning comes anywhere near your boat there will be enormous induced currents in almost every piece of wire in the boat.

That is why I was questioning the advice to bond all skin fittings together - the current induced in the bonding wire could do more harm than good, and you could also be causing unnecessary galvanitic problems.

As to connecting the chain to the anodised mast - if the objective is the help divert the force of a strike then you don't need to worry too much about the quality of the connection as the voltages involved will be enough to get through a bit of oxidation. If you are using genuine lightning conductor they the resistance of the path to earth is probably more important

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