Lightning protection

[DanTribe]

Having had almost all of the electronicals on my boat fried, I thought that I would try and find out how to prevent it happening again.
I have searched the web and come up with lots of very useful info, but much is in very technical terms. It also seems to me that for every bit of advice, there is a contradictory one.
Does anyone know of an easily understood explanation of what should be done?

When you think about it, surely it's surprising that there aren't more strikes as most boats have aluminium poles stuck upright in brine.

Dan


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[ccscott49]

Even if you have a lightning conductor, chains on the shrouds etc etc ad infinitum, the elctro magnetic pulse, will still fry all your electronicals! So why bother?

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[Moose]

MoBo's have sufficient lightening protection in the form of all the yachts around them with great big masts.

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El Alce

 

[Roberto]

If your concern is saving electronics, I do not think there is much that can be done. Some have successfully tried to put theirs in the microwave oven, I am still on the traditional side of cooking though.

For other kind of damages, I have been struck on a keel grounded mast boat and people have been unharmed so I stick to that, besides the probability of being struck twice are comfortably near to zero(!)

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[vyv_cox]

This is a subject in which I have a great interest. If you search the archives you will see that it has come up many times. The truth is that nobody knows the answer. There are several proprietary devices intended to protect boats from damaging strikes and almost as many case histories that show them not to work. Perhaps the most thorough treatment of the topic is to be found here It's slow to load but it was working when I last looked. Nothing to do with boats, but spectacularly good.

My thoughts on the lightning conductor argument are these. Dropping lengths of chain attached to shrouds over the side may turn a mast into a conductor, although whether a 2 - 5 km lightning strike will be influenced by my 15 metres sounds a somewhat arrogant supposition. However, if a deck-stepped mast is largely insulated from the sea, why tempt providence by making it a conductor?

Then again, as said above, the mast does not need to be struck to destroy your electronics. I have received a good belt when holding the forestay of a boat and lightning struck a hill at least 1 km away.

Ultimately I believe it is largely influenced by luck. If your name is on it, you'll get it.



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[vyv_cox]

My late aunt was struck twice by lightning, both when hill-walking. On one occasion she lost all the skin off her forefinger and on the other she was rendered unconscious for a short time. She survived for many years afterwards.

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[coco]

It is very hard to know what will happen. In 2001 we were approaching the St-Tropez peninsula from the west. Thunderstorm clouds were at an estimated distance of 20-30km. Suddenly you could get sparks out of the rigging by approaching your hand. After having moored in the harbor we noticed that the whole B&G electronics and the battery charging system were damaged (unusable), but the portable VHF (Simrad) connected to the masttop antenna and to the charger was still working perfectly. We still dont know why the selective destruction with thunderbolts so far away.


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[Roberto]

Now I understand where that Marvel super hero comes from !

Funny story, no idea if it is true just heard: one couple were romancing the *safe way* on a hilltop when they were struck by lightning, apparently they needed a long surgical intervention to remove all the melted plastic that glued them sooo close together.
Was their electronic wristwatch working ? that's what matters..

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[DanTribe]

By 'eck, that could make you paranoid!
I once saw photos of a couple wrapped up in chains, so obviously they were taking precautions against lightning.

I'm beginning to wonder if it's safe to go out, as sailing, angling, golf and outdoor nooky are all so dangerous!

Dan

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[richardandtracy]

Thunderstorms build up huge voltages over the entire cloud, you only get lightning when the the voltage is high enough to ionise a contiguous trail. These wide area charges are what caused your electronics problems.

When at school in the summer of 1976 I measured a current of 10 amps going up the lightning conductor into clear air. No storms visible, just the effects of ionisation due to normal clear air thermals and turbulance. The current died to almost nothing after dark on that day.

Regards

Richard


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[William_H]

One text book suggested you need at least 2 square foot of conductor underwater connected by heavy copper cable to the mast . The current in a strike can be huge and the resistance of the stainless steel stays means that chain into the water will dissipate only some of the power. I disagree about the electromagnetic pulse. I am told that each jet airliner is struck on average once per year generally with no damage or minor burning and electronics survive with out problem. I would suggest you had electronics on the mast head and electronics in the water log depth sounder and that the best current path from the mast to the water was via the electronics. A good grounding of the mast may have saved your electronics. I reckon if it can happen once it can happen again so would suggest some sort of mast grounding.

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[ccscott49]

Aeroplanes are not connectd to the ground when they get struck, different matter if they are, ever seen one struck on the ground? I have, it was a right off, there wasn't a piece of wiring left intact in the whole aircraft, nor any eletrical components worth a damn.

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[oldharry]

Added to which modern aircraft are designed to withstand lightning strikes while flying - particularly their electronics and fuel tanks. My knowledge is limited to 2 - 3 interesting TV programmes about it - but I dont ever remember seeing lightning strike protection in a boat specification....?

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[DanTribe]

Re: Thanks for all the input

All very helpful and appreciated, but this subject seems to generate two more questions for each answer.
The University of Florida site recomended by vyv cox is good and explains the problems in terms I can understand. I'm not sure I like the idea of bonding all metalwork [mainly aluminium] with copper wire, surely an electrolysis problem.
In my case a keel stepped mast sits on a GRP pad, a few inches above a lead fin keel. Presumably bonding them together would give a good path.
William H 's theory about the path via the echo transducer seems logical, except that the sounder was the only thing still working.
I understand from the electronics manufacturers that this is a fairly common problem, in which case it's surprising that insurance companies don't give some recomendations about best practice.

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[Gunfleet]

no, they'd fouled their anchors

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[jfkal]

Re: Thanks for all the input

There is a lot of nonsense around on the topic. In a nutshell that's what you have to do:

1. Passive protection
Ground the mast solidly to the keel (bridge the gap if deck stepped with a solid aluminium wire down to the comression tube and from there to the keel).
Connect as many chainplates as you can access down below to the keel as well (or a grounding plate if you want to pay the money for it {do not use the grounding plate of your SSB for that, please)}
This provides a solid path if you get struck (does save you but not the electronics (see point3 )


2. Preemptive protection
Install an ion dissipator at the top of the mast. Looks like an upside down steel brush. It will to a certain extent prevent "streamers" from building up by lowering the level of ionisation of the surounding air thus reducing the risk of a strike.
Mast has to be properly grounded for this to work

3. Active protection

Install electronic devices into all relevant circuits (General DC, GPS, VHF, Radar) which will "ground" any voltage higher than the operating voltage in order to supress the EMP effect in conductors parallel to the strike path.

Enjoy sailing and a low insurance premium.

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[coco]

Re: Thanks for all the input

"Install electronic devices into all relevant circuits "

What are these devices? Where available?

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[jfkal]

Re: Thanks for all the input

Hi there let me have your direct e-mail address to jfkal@pacific.net.sg and I will attach a few pdf files for those who are interested.
The "devices" get hooked between i.e. the GPS antenna (an obvious target) and its instrument and will mop up all transient voltage spikes on any of the connection leads between them.

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[William_H]

The lightning protection for an aircraft consists in having the entire sructure bonded with low resistance conductor so that current can pass un hindered into and out of the structure. Carbon fibre or fibreglass structures have a conductive mesh molded into the skin near the surface. The radome usually fibreglass for radar transparency has strips of aluminium from near the front, back to the fuselage. Yes most lightning strikes on aircraft are part of the cloud to cloud discharge. I can't comment on the aircraft destroyed on the ground unless it was a small wood and fabric type.
Radio systems have either a DC grounded antenna or a spark gap type overvoltage protection. I know of no overvoltage protection for power supplies to radios or other electronics. I suggest therefor that this type of protection is not necessary for ship elecronics. I do have these devices on the 250V mains into my house to protect from voltage surge its called Metal Oxide Varistor .
An aluminium strap from mast base to keel should provide all the protection you need however the dissipation device on the mast top may have value. Aircraft use these devices on trailing edges to dissipate static electricity build up. This is to prevent radio interference if static builds to a higher voltage before it discharges.
A prop jet aircraft recently was struck onto a propeller tip with apparently no damage. Some time after it was found that the high current through the propeller blade pitch change bearing had softened the bearing balls A failure here would destroy the aircraft possibly weeks after the strike. The moral is if you have a lightning strike look for problems in the rigging caused by the high current and heating effect of aluminium and stainless steel. Damage may not be immediately obvious.

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[ccscott49]

There was a helicopter crash, here in the north sea, killing a bunch of people, because of a lightning strike, not what caused the aircraft to crash, but long before, which weakened the rotor blade, which was not seen on inspection. The huge electrical discharge of a lightning strike on a boat, will probably still fry everything electronic and as you say, the rig would bear inspecting aswell. I'm not sure what any of these so called protection devices would achieve, I'm certainly not up for testing them!!

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