Lightning protection for you boat

[GTom]

Originally Posted by Hobschel

i was thinking exactly the same, so a carbon mast and spectra rigging would lower the chance of being hit... but if it would be worse...

Someone has to come up with a decent solution to channel the lightning from the top of the mast to the sea. DDCE and alike solutions will stay in "snake oil" category for me until I see MILLIONS of installations around the world and insurance reports on their actual efficiency. Till then, we stay with the good old Franklin rod/aluminum mast, which indeed attracts lightnings. Accordingly we have to take care of the consequences and make sure the lighting doesn't blow the through-hulls and sink the boat.

What about the microgrid type used for aircraft?

Originally Posted by transmitterdan

The PDF says $300.00 per year. No mention if that includes travel costs and tower climbing costs. Also, it seems hard to understand exactly what the inspection entails. Measuring 10 ohms resistance between what and what? A ground resistance of 10 ohms is actually pretty high in my experience so it's probably not that.

I am 100% sure, that they won't send an engineer/surveyor to a Caribbean island for 300 bucks total cost... Sounds like they have a 500k$ special "lightning insurance deal" for themselves for 150$ and they pay a surveyor 150$ to check if everything is OK.

[TreblePlink]

Originally Posted by GTom

That's nothing extreme: Round Wire Resistance Calculator

< 10 ohms - It's not the wire that is the limiting factor; it's the amount of conductor surface area in contact with non-current saturated seawater.

[GTom]

Originally Posted by TreblePlink

< 10 ohms - It's not the wire that is the limiting factor; it's the amount of conductor surface area in contact with non-current saturated seawater.

True, contact resistance has to be taken care of with a proper grounding plate.

[GordMay]

Originally Posted by transmitterdan

... A ground resistance of 10 ohms is actually pretty high in my experience so it's probably not that.

Ideally, the ground resistance shouild be close to zero.
The National Electrical Code requirement, in Sec. 250-54, requires the resistance to (earth) ground of a single-made electrode (e.g., ground rod) to be 25 ohms or less.
In facilities with sensitive equipment it should be 5.0 ohms or less.
The Telecommunications industry has often used 5.0 ohms or less as their value for grounding and bonding.

[TreblePlink]

Originally Posted by GordMay

Ideally, the ground resistance shouild be close to zero. ...

Absolutely. There is no question that the lower resistance, the better. Metal hulls probably approach this ...

[NevisDog]

Originally Posted by Hobschel

i was thinking exactly the same, so a carbon mast and spectra rigging would lower the chance of being hit... but if it would be worse...

You do realise that carbon fibres are good conductors of electricity (unlike glass fibre for example)?

[TreblePlink]

Also remember that in-mast wires for antennas and lighting mean that it's pretty much impossible for your mast to be non-conductive.

The main premise of lightning protection is not strike prevention (although there is some anecdotal evidence of the "wire brush" dissipation array helping to some degree) but rather to provide a preferred path for the current to reach seawater - one that is the least destructive.

[transmitterdan]

Carbon fiber masts are made of conductive and non-conductive materials. Therefore they present a special challenge when lightning strikes. The carbon fibers twist and turn and the lighting current wants to run straight down the mast. So it will often jump from one fiber to a nearby one. This heats up the fiber and the resin and can reach temperatures that exceed the rating of the resin. It can even break the tiny carbon filaments. The result is a weakened structure that may be very difficult to observe since the damage can be confined to inner layers of the layup. Consult with the mast supplier about best practices for lightning.

[mikedefieslife]

Originally Posted by TreblePlink

Also remember that in-mast wires for antennas and lighting mean that it's pretty much impossible for your mast to be non-conductive.

The main premise of lightning protection is not strike prevention (although there is some anecdotal evidence of the "wire brush" dissipation array helping to some degree) but rather to provide a preferred path for the current to reach seawater - one that is the least destructive.

I thought it was mentioned in another thread though that unless the wire you provide is about as thick as your leg it's going to do sod all in terms of protection. Of course I could be very much mistaken, but it's something I remember from the lightening thread (that included monos) a month or so ago.

I wonder what stats say about boats cruising 30 years ago to now. Back then I imagine very few boats had any sort of factory lightening protection at all, but still had electronics on board.

In fact, do modern multihull manufacturers build in any lightening protection? I know mine didn't but my boat is 40 years old, at the time though they were one of if not the largest catamaran producer around.

[SailFastTri]

Originally Posted by transmitterdan

Carbon fiber masts are made of conductive and non-conductive materials. Therefore they present a special challenge when lightning strikes. The carbon fibers twist and turn and the lighting current wants to run straight down the mast. So it will often jump from one fiber to a nearby one. This heats up the fiber and the resin and can reach temperatures that exceed the rating of the resin. It can even break the tiny carbon filaments. The result is a weakened structure that may be very difficult to observe since the damage can be confined to inner layers of the layup. Consult with the mast supplier about best practices for lightning.

Do you have the experience or research to back this statement? It sounds like it might be opinion or generalization, based on ???.

Originally Posted by mikedefieslife

I thought it was mentioned in another thread though that unless the wire you provide is about as thick as your leg it's going to do sod all in terms of protection. Of course I could be very much mistaken, but it's something I remember from the lightening thread (that included monos) a month or so ago.

I wonder what stats say about boats cruising 30 years ago to now. Back then I imagine very few boats had any sort of factory lightening protection at all, but still had electronics on board.

In fact, do modern multihull manufacturers build in any lightening protection? I know mine didn't but my boat is 40 years old, at the time though they were one of if not the largest catamaran producer around.

It's pretty well established in the research papers of lightning "experts" that AWG#8 is sufficient to conduct a single strike and AWG#4 is sufficient to withstand multiple strikes. Either one is a lot thinner than a leg.

"do modern multihull manufacturers build in any lightening protection?" Generally not, but it can be added. Much easier to do during manufacture, before the hull interiors are finished.

[TreblePlink]

In-mast radio and light cables are unavoidable, and by themselves will conduct strike energy to your radio and DC systems. This is not the preferred current path.

If I had a semiconducting carbon mast, I would use 4" x 0.032" copper strap between the mast top and my keel bolts.

I use this regularly at broadcast tower sites - it has very low inductance - which is good for the fast risetime lightning pulse. In my industry it is generally considered best for grounding and bonding. Georgia copper sells it.

[transmitterdan]

Originally Posted by SailFastTri

Do you have the experience or research to back this statement? It sounds like it might be opinion or generalization, based on ???.

snip

It's pretty well established in the research papers of lightning "experts" that AWG#8 is sufficient to conduct a single strike and AWG#4 is sufficient to withstand multiple strikes. Either one is a lot thinner than a leg

I know that carbon fibers are conductive. I also know that the fibers are not all in a straight line. I also know the resin is made of nonconductive material. I also know that carbon fiber masts can be damaged by lightning. Any damage is sometimes hard to find by a simple visual inspection. It is not an opinion but based on talking to riggers and my engineering knowledge of composite materials.

In my opinion AWG #8 is insufficient diameter wire for lightning protection. I think today's experts agree with that. Years ago #8 was recommended and many boats have that. I think #8 is ok If the wire is only a few inches long. For a few feet run flat copper strap 2+ inches wide is the "best".

[transmitterdan]

There are conductive additives used for making external aircraft parts to help mitigate damage from lightning. I haven't heard of any carbon spar makers using this. Hopefully soon they will begin doing that for boat masts.

[mikedefieslife]

Originally Posted by TreblePlink

In-mast radio and light cables are unavoidable, and by themselves will conduct strike energy to your radio and DC systems. This is not the preferred current path.

If I had a semiconducting carbon mast, I would use 4" x 0.032" copper strap between the mast top and my keel bolts.

I use this regularly at broadcast tower sites - it has very low inductance - which is good for the fast risetime lightning pulse. In my industry it is generally considered best for grounding and bonding. Georgia copper sells it.

Which keel bolts? This is the multihull forum section and I'll bet most will be catamarans.

Most catamarans have an on deck stepped mast, and modern ones have a massive freeboard. Any wire from the base of the mast to a plate on hull in the water is likely going to have to run 3 meters minimum, more like 8 meters to get tucked aways properly.

[TreblePlink]

Sorry, I was speaking of my boat. In the case of a cat, gotta have submerged metal. I have seen wooden hull boats that have sheet copper applied to their hull for worm protection. Lightweight and very conductive, this might be a good choice for a multi hull.