Lightning protection for a catamaran

[chris14679]

Originally Posted by JoFi

Thank you guys, this is a very informative threat for me!
We have a carbon mast on our catamaran and plan to use a carbon rod instead of alloy. Any thoughts on that?

It's better NOT to ground a catamaran's rig, you're much more likely to attract a lightning strike if your rig is grounded. Make sure the rig is well insulated and isolated from the water so you don't attract lightning.

That's the TLDR version of my earlier post.

[Mike Banks]

Your carbon fibre mast is not metal, so it will not matter if you use copper or aluminium on it. Since you are concerned over weight, perhaps the alloy would work, but I would be using copper in your situation all the way, it is heavier, but the copper discharge plate in the water will keep itself free of most marine growth.

If you wish to use alloy, that will work too. I would certainly run an additional lightning conductor and not use the carbon fibres in the mast as a conductor.

The whole idea of lightning protection, is not to collect and discharge a major strike. There is no lightning protection system that would do that--I have seen a multi-conductor lead sheathed one thousand pairs of twenty pounds per mile telephone cable completely vaporised and absorbed into the surrounding soil by what was only a moderately powerful strike, and a cow that had been grazing a couple of feet above it was also dead without a mark on it, so it must have provided some sort of shunt pathway as well.

The idea of a lightning protection system that works (and most of them do to some extent) is to conduct to earth any possible electron pathway of ionised charged moisture, dust and salt laden air that may potentially provide a strike discharge pathway to your building or vessel at sea--and the ocean is a much better sink, being an electrolyte, than is the earth in most places.

In the same area as where the cow was killed, I later installed gaseous arrestors in a metal cabinet where open aerial suspension cable was used because of rock outcrops that made buried cable impractical. It was a known lightning hot spot, and after that was done one could often hear the crackle of these low pressure tubes discharging to earth the accumulated static charge of each protected circuit.

Which is why I think a gaseous arrester would work connecting copper lightning protection in the water to an aluminium mast--as soon as the charge potential reaches about one hundred volts or less, we used 100 volts because the circuit voltage ring and alarm circuits were eighty volts--the self-triggering arrester fires a bit like the tube in an electronic flash unit, and continued to conduct until the charge potential is down to about eighty volts or so.

[Morndenkainen]

I worked at a prison for a number of years as a C/O, and maintenance officer. We had rather tall floodlights scattered all around the compound, 200ft light masts, and they had a lightning strike protection system on them. That system was composed of multiple 0/0 gauge copper cables that ran from the mast to grounding rods, about 10ft into the ground, and then spread out about 100ft in all directions. If I recall, there were 8 of those cables on each mast.

Several of the masts were hit multiple times by lightning over the 4 1/2 years I worked at the prison. None of them suffered any major damage, a couple bulbs burnt out, usually fried the grease on the pulley wheels, but again, nothing serious. The steel cables for raising/lowering the mast head, and the motors/pulleys never melted and always worked, so there's that.

Now, what's your plan to get that much copper from your mast, down through your hull, and give yourself enough surface area to disperse all that current? I'm not saying I don't believe it can be done, but it's going to add some weight to the boat and be pretty difficult and expensive to do.

If I had to guess based on personal experience from work, Perhaps if you covered the keels in 1/8" thick copper sheathes and ran 4 of the 0/0 gauge welding cables from the mast to the bottom of each keel (think contact area between the cable and copper plate) you'd be in good shape... But, then you've also made your boat a magnet for lightning strikes as well, as you're now the best ground within at least a good 1/4 mile if not more. The prison certainly was.

[GordMay]

Originally Posted by Mike Banks

Your carbon fibre mast is not metal, so it will not matter if you use copper or aluminium on it...

These papers might be interesting & informative:

“Galvanic corrosion of Al/Cu meshes with carbon fibers and graphene and ITO-based nanocomposite coatings as alternative approaches for lightning strikes” ~ by B. Zhang et al
➥ https://link.springer.com/article/10...170-012-4568-3

“Galvanic Corrosion of Metals Connected to Carbon Fiber Reinforced Polymers” ~ by Mehdi Yari
➥ https://www.corrosionpedia.com/galva...olymers/2/1556

[Frankly]

Originally Posted by Morndenkainen

Now, what's your plan to get that much copper from your mast, down through your hull, and give yourself enough surface area to disperse all that current? I'm not saying I don't believe it can be done, but it's going to add some weight to the boat and be pretty difficult and expensive to do.

Assuming aluminum mast on a sail craft floating on/in ocean (ie salt water), the mast is more than capable of safely conducting the current from most lightning strikes.

Seawater is a much better conductor than most soils so the problem in that end of things is much easier to solve.

As to cats, the yacht geometry is a complication but not hopeless. Carbon fiber masts going to need a significant electrical conductor to the mast head. Anchor light circuit not going to cut it in most cases.


Frankly

[JoFi]

Originally Posted by GordMay

These papers might be interesting & informative:

“Galvanic corrosion of Al/Cu meshes with carbon fibers and graphene and ITO-based nanocomposite coatings as alternative approaches for lightning strikes” ~ by B. Zhang et al
➥ https://link.springer.com/article/10...170-012-4568-3

“Galvanic Corrosion of Metals Connected to Carbon Fiber Reinforced Polymers” ~ by Mehdi Yari
➥ https://www.corrosionpedia.com/galva...olymers/2/1556

It sounds to me like it is not a bad idea to connect a carbon fiber rod to the base of my CF mast and have it lowered vertically into the seawater. But how to connect the rod to the mast? Stainless steel fitting? And how to assure a low inductance connection between rod and seawater?

[carstendenmark]

Mike Banks, could you please provide a sketch or photos, to show your plate and the connections ?

I have the idea of doing the same on my deck-stepped mast on my monohull, leading the wires from the mast to the shrouds, and then to alu plates on port and starboard side, into the water. Just to be attached, when the danger comes...

I have another ongoing thread :
Electric propulsion - lightning protection ?