Lightening Protection

Close hauled

Close hauled

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Having recently been on the wrong end of a lightening strike I am very keen to prevent it ever happening again.

From what I've read there isn't any agreement on what works best and even Nigel Calder admits its as much an art as a science.

I've heard good things about Strikeshield from Seyla Marine.

Any experience, advice or comments would be welcomed.
 
I can't see that there is any way to ground a boat effectively from a strike or even near miss. Turn off the electrics and put any removable/portable stuff inside a wire cage or oven. About the best you can do.
 
Being in Johannesburg and summer is just starting this is our lightening season and every year I have some electrical equipent damaged and so have spent a lot on protection.

I think you are looking at lightening conductors to fit on your mast. We have lots of thached housed with lighting rods to protect the roof.

The general view is that there is a cone of protection with the point of the cone at the point of the lightening rod and the greated the distance between the surface of the cone and the item protecting the better.

I have looked at these devices and the theory of OK but the mounting is not high enough to give good protection as it must be alot higher the the highest point on the mast which in most cases id the VHF aerial and being metal would affect the operation of the aerial. If there was a strick and this unit would have to be connected to the ground (sea) by a very strong wire the current flow would indice a high voltage in wires in the mast that would damage any equipment connected.

I had a lightening strick on my house once and the earthing canle from my TV arial was 6 sq mm cable and the copper melted completly.

I think this unit is too little to be realy effective.

To protect electrical equipment from induces surges, the general view is transorbes and gas aressters and lots of them
 
As far as my ancient electrical engineering degree once taught me, there is no guaranteed protection from lightning. The best method in theory is to have as many sharp points as possible positioned higher than anything else. Lightning forms by a build up of charge at the surface, attracted by an opposite charge in the cloud above. If this charge grows it can exceed the breakdown strength of the air, 30kV/cm dry, which can then discharge as a "strike" which, incidentally, flows upwards from the site of the strike. If you have a number of sharp pointy things then the charge is dissipated more gradually (corona discharge) and reduces the likelihood of a "strike". Whether it offers real protection depends on the rate of charge buildup. If its slow enough then spikes will prevent a strike. Further protection should be available if you can provide a low resistance path to earth (which can be the sea).

If the resistance is not low, then the large (20000A) current flow will produce high voltages on the conductor, increasing with distance from earth, which can be high enough to leap across gaps to a neighbouring earthed object, often a yuman bean.

Don't stand close to your mast in a storm.
 
correct me if I am wrong. There are two issues in terms of practical things you can do. Install a system to reduce the potential for a strike or install a conductor to deal with a strike. Since it is really difficult to install a big enough conductor we would be better installing something to reduce the potential for a strike?
 
You are not wrong. My above post is talking about both ideas. Spiky things to reduce the risk, low resistance path to the sea in case you still produce a strike. Some say that a good length of chain around the mast and dangling in the sea can reduce the current flow through your boat.
 
PS to the above: a "lightning conductor" as seen on church roofs for example, is the aforementioned means to REDUCE the risk, and is always a sharp pointy thing. The copper strap running down the side of the building connecting the pointy bit to earth is simply conducting the corona discharge, which hopefully dissipates the impending flash before it starts. If it gets a strike anyway, then my guess is the copper strap will melt and part anyway.

The biggest cause of damage to building materials is allegedly the destruction caused by rapid heating and evaporation of trapped moisture in the brickwork, often explosive in nature. I imagine this would be similar in various parts of boats.

The cone of protection mentioned earlier is true enough, based on the fact that your pointy things are less effective the more you are laterally displaced from them. The single un-insulated cable that connects power transmission pylons at their highest point gives protection from the cables below, in a similar manner, and is connected to earth via the pylons.

I've just about exhausted my entire memory of HV stuff now, you will be glad to hear!

Pops
 
Please, please can everybody spell lightning correctly!! Oops, I do not mean to offend!
--------------------------------------------------------------------------------

It jumps out at me, but I decide that I'm being pedantic owing to having taught English for rather too long.
 
The definitive work for lightning protection on buildings is BS 6651

In principle this says that a Faraday shield is the way to protect a building.

From memory this involves putting a mesh of (i think) 10m square on the roof and connecting each wire of the mesh to earth.

If you consider a yacht then the mast and rigging form a reasonable facsimile of a Faraday shield - assuming the rigging is metal. Perhaps could improve by dangling copper wires into 'oggin but probably not worth the effort.

When you consider there are said to be 3 billion lightning strikes on earth every year and damage to yachts from lightning is relatively small there would seem to be some weight to the argument.

Take care with the words - being struck by lightning is very rare. So that fitting any means of protection is at best making a low probability even lower so that statements of the "never had a strike since it was fitted" have very little meaning.

You can get surge protectors that will fit in the coax to the VHF (or TV) antenna which will give some protection. Not sure about radar instalation - If not built in then probably best left alone.

Mast head wind instruments probably not worth the cost/efort of protecting.

Batteries will give a reasonable level of protection against any surges induced in the DC power system, and mains suge protection can be fitted in the mains supply.

Lots of suppliers - Google surge protection.
 
Some time ago (approx 2002) there was a long string on here which interested me as I had sailed through a number of thunderstorms off northern France. After reading lots of advice the only change I made was to take an old (metal) biscuit tin with me. If I see any sign of lightning, I put handheld VHF and GPS plus a phone into the tin and put it down below. As I've never been hit I dont know if it works but it does make me feel a little better.
Allan
 
After complaining about the smelling of lightning was your smelling of "yuman bean" tong in chek??

I have only 2 finger typing skills I wish they would not confuse me further by moving the keys on the qwerty keyboard!!
 
Ha ha! Nice one, Centurion. I wasn't really complaining, just pleading! Out of the hundreds of smelling mistakes on these forums it is only "lightening" that drives me mad, being an ex-eleccy. I hope no-one was really offended.

Pops
 
As I understand it, when the water molecules (clouds) bounce around against each other they build up a charge - let's say it's a negative charge. So the sky above has this massive negative charge - since like charges repel each other it pushes all free electrons (negative charges) away, thus causing all things around (including your mast) to become positively-charged. Air is a pretty good insulator, so the charge has to build up until can overcome this insulation. In fact the air molecules start to align themselves into conducting conduits of plasma. These plasma 'feelers' reach up from the positively-charged items on the ground, and down from the negatively-charged clouds; when two of the feelers make contact, the circuit is complete and a lightning bolt shoots along that path. Your spiky 'static dissipators' supposedly discharge that positive charge buildup - I'm not sure it works that way. I think having many little spikes just disrupts the formation of the positive feelers. I don't think grounding the mast will necessarily reduce its positive charge either, as the earth's surface in the vicinity will also be positively-charged. I think the static-dissipation devices may work - in a marina, they make your boat less conductive than the unprotected boat next to you. But if you're out by yourself in the oggin, I don't think they'll keep you from getting hit. That's where the 'damage-mitigation' hardware and procedure comes in, as previously discussed. As for Faraday cages - chalk up one more positive aspect of metal boats.
 
I blame "cut and paste" and I am sticking to it.

I am a mechanical engineer and not spelling correctly is a requirement !!! Again thats my story, etc
 
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