How To Avoid Ligthening Designing A Sailing Yatch

Sorry Eric,
I did not want to sound too disrespectful, If I did , I apologize, we foreigners have our hiccups with English sometimes, but there are not many boat builders who have lightning protection high on their list of importance. If I had to do an Atlantic or any Ocean crossing, I would have requested the boat builder to incorporate mesh wires in the GRP of the cockpit with proper safe low resistance connections with the earth/ground/water, creating a safe Faraday cage environment. Not many people understand and have experience with lightning strikes, thus their earthing and important earth connections are neglected until it is too late. A lot of people want to suppress a strike, while the trick is to re-route the strike. Bert

 

I suggest that if you have an aluminum mast, you don't need the wire down the mast. But keep the wire from the base of the mast to the plate in contact with the water.

I wouldn't do anything (like mesh) to encourage lightening to travel inside of GRP.

 

Agreed

That is the problem, when lightning strikes are not fully understood. Are you worried about heat development, if mesh is incorporated into the GRP? It depends totally what the resistance of the mesh Faraday cage is. If you have a 0.001 Ohm resistance from the top of the mast, rerouted to your ground plate and a mesh wire connected to the ground-plate with a different cable and having 0.1 Ohm, I guarantee you that you will not have any lightning flashing side ways. Also the energy induced into the mesh compartment is low and will not heat up.

50.000 Ampere x 0.001 Ohm = 50 Volt from the top of the mast to the ground-plate. Nothing is going to jump, no flashes. However, if you have, like most people a 1 Ohm connection, because of corrosion etc. , you looking at 50.000 Volt and therefore you will get sideways flashes jumping to positions which have a lower path resistance and then you will get 50.000 Ampere through your mesh wire. 50.000 Ampere x 0.1 Ohm = 5000 Volt, with an energy of 250 Megawatt for a fraction of a second. That will heat your cockpit up and you will have a meltdown.

The trick is to re-route the lightning strike via the lowest resistance, with the least bends and curves. You will survive. The reason why I like to have a mesh wire is logical. A current of 50.000 Ampere through the mast , will induce a nice voltage potential in your body, although your body with the mast is only an "air" transformer. This when you are standing close to the mast of a few meters or standing in your cockpit (without mesh wires). During lightning make yourself as small as possible or lie down horizontal, does that make sense? Bert

 

Thanks Bert, you beat me to it. Using just a mast as your conductor is a really foolish idea. I've been aboard for two strikes, one with protection, the other without. The boat with protection (masthead rod, cable and ground plane) had some burned cable clamps, scorch marks and other minor issues, no serious damage, the other took the hit at the masthead crane, blowing it right off the pole. The voltage continued down to the deck mounted step and blew through the deck and arced to the centerboard pivot assembly. The rig came down, the boat was holed, the crew knocked out for several minutes, just to awake out of sorts, in a helpless boat that was taking on water.

This sort of information is fairly easy to look up and make practical preparations aboard any vessel. Using foolish wife's tail concepts, like assuming your rigging or mast will serve, is just asking to be a statistic, on a list of the latest victims. Where I live is the USA's lightning capital. In an average summer thunderstorm, we can have hurricane force winds and 20,000+ strikes in an hour. Sailing through this regularly, it's become routine for most of us, but if you've never experienced it, you'll be horrified during the event.

I've inspected many boats that have received a strike (it's pretty common here, imagine that). If proper protection is in place, there are some obvious replacement issues, but most boats fair well. If there's no protection or silly ideas incorporated into this system, the results are usually a total lose or heavily damaged yacht.

 

So guys what is the best practice as a result of those mentioned issues? I have a 6 meter small catamaran and I am afraid of burning at the sea. Thanks.

 

Metin, your original post was about avoiding lightning strikes by design, but now you seem to already have a boat.

Luckily it is a small one, so the chance that a thunderbolt will strike you is very slim. Lightning discharges prefer tall and conductive objects; only if you are all alone at sea and happen to be in the wrong place and time you might get fried and there is very little you can do against it.

 

Ok I designed my catamaran but afraiding Lightning. Consequently I will decide whether I need to modfy my design.

 

My apology PAR for stating that boat builders don't have good low resistance lightning protection high up their list, at least you have. I wonder how many sailors have measured the resistance from top of the mast to the water with a earth ground measuring instrument borrowed from an electrician. A unit with all those electrodes , which you drop on a floating object in the water and extend the main wire to the top of the mast. Before you measure you should calibrate the instrument. Thereafter it is a simple calculation 50.000 x resistance = Voltage potential, although 50.000 Ampere is what we have maximum measured in RSA, there are places in the world where it seldom could go up to 60.000 Ampere. If the calculated voltage is less than 3000 - 4000 Volt, you should not have flashes jumping, over the 10.000 Volt, you have probably a problem. Also how many sailors have checked , whether the ground plate is actual properly connected to the seawater and that all the connections have low coupling resistance, I don't think too many. Thus don't blame the lightning strike, blame yourself that you forgot to check. Bert

 

If you are still in the designing stage, you should mount a very good copper thick wire, like an stripped thick electrode cable from a welding machine and connect this the shortest possible way from top to the ground plate (It must be properly connected under water) If your ground plates are at the side of the Cat, you go for 2 cables to each of the ground plate. I prefer that even more, than a single copper wire going through your cockpit.
But if you will be going onto the Ocean, small boat or large boat, you are the highest point in the area and that will make you a target, when not properly protected. Do yourself a favor and get some opinion from Lightning protection experts in your country. I would not go onto the Ocean without knowing the measurements of the resistance from top of the mast to the water.
Bert

 

this is how my boat is like

The wooden catamaran which I designed and builded. Sailing equipmet has not finishes yet.

 

Hi Metin,

There are two philosophies.
1) You make sure that very little metal parts are on the boat and you have a wooden mast with nylon ropes from the top to the hull. You don't have any connection to seawater. Excellent, but it has ONE flaw, if it rains, your equipment gets wet and then you are "sitting duck" or "easy pray" as you will be the highest point at sea.

2) You make sure that you have a decent lightning protection and what I can see from your boat, you don't have a cabin. The only way ( the way I see it) if you are really so crazy to cross the Oceans with your boat, make a Faraday cage to climb in when the lightning surges becomes too close. You count the time between seeing the lightning and hearing the flash. If it is less than 3 seconds, climb in your Faraday cage and with dry gloves and nylon ropes control your boat. If you design the boat wires so, that it becomes a Faraday cage in that case you also have a problem. If you heel, your Faraday cage becomes nil and void. In that case lie flat on the hull, you may have a 1 % chance to survive otherwise put me in your will, I will make easy money. You need to do some research on lightning discharges.

If I was in your shoes? I would make a platinum point with 2 thick copper cable straight down to the water on both sides of your hull. I would make a Faraday cage I could climb into and hold it out until the lightning has passed. (Make sure no body parts can stick out)
Bert

 

off the wall question

Would Bronze window screen make a useful faraday cage if used on an aluminum frame, such as a bimini top frame?

 

I cannot advice, unless you comply with http://science.howstuffworks.com/faraday-cage.htm

Aluminum could probably be used.
Bert

 

Some notes from various sources:

The mast, if constructed of conductive material... can serve as the air terminal.

An aluminum mast is the preferred down conductor...

If your sailboat is a vessel with an aluminum mast you have the starting point of a well-grounded lightning rod.

Use #4 gauge copper wire to connect mast to ground plate, #8 is marginal.

Fresh water requires much larger ground plates.

Measurements made of the current flow in the lightning strike show that 50 percent will have a first strike flow of at least 18,000 amperes (18 kiloamps, or kA), 10 percent will exceed 65 kA, and 1 percent will have a current flow over 140 kA. The largest current recorded was almost 400 kA.

 

You could also consider something like this.

http://www.hollandshielding.com/158-EMI_RFI_shielded_Faraday_tent-en.htm

The sheets hanging downwards are metalized.
Bert