Carbon masts and lightning

[Richard Woods]

Many months ago there was a debate here about the damage caused to carbon masts by lightning.

Some people believed that a carbon mast would not be damaged by lightning. Maybe this, taken from a recent Latitude 38 will change their minds

There was a horrendous lightning storm, with huge bolts striking all around Coyote. We finally took a direct hit. The bolt came down the carbon fiber mast, blowing a hole in it, and showering the forepeak — where the woman was trying to hide — with sparks from the windlass.

The bolt continued up the mizzen to the radar, then down to the engine. I could see it all even thought I had my eyes shut. Finally, after the deafening noise, there was dead silence.

Then I heard the comparatively soft sounds of things like lights and antennas falling off the masts and onto the deck. Finally, all the pumps in the engine room started going on and off of their own volition, and the hull sounded like Rice Krispies in milk.

Coyote is actually a Freedom 40 monohull, not that that makes any difference

Richard Woods of Woods Designs

www.sailingcatamarans.com

[ThomD]

Last summer I was gazing out the window at our lake, and heard a large explosion followed by what looked like a truck load of 2x4s projected down the beach. A lightning bolt had just hit our large ash in the front yard, and framents, large logs some of them, could be found a hundred yards away in the surrounding fields. Our house was lucky, because the segment blown out of the tree had been on the far side, and no damage was sustained by the house. On the other hand, had anyone been within 30 yards of the claymore effect, I think they could have been killed. So I guess ash is out also.

[powerabout]

There was a boat in Brighton marina in the Uk last year that had a direct hit ( assumed) and the mast turned to powder, the spreaders and rigging ended up on the deck and black power on all the boats down wind.

[powerabout]

How ya gunna feel in a lightening storm in the Boeing dreamliner?

[powerabout]

One of my friends did Mech eng in the uk where they have a vandergraph that can create lightening type sparks and tested carbon masts with a vendor.
They found if the mast was completely covered in epoxy and no carbon exposed, the mast usually survived BUT if the spark can get to a fibre it will burn it and move to the next and so on very quickly so you end up with a tube of epoxy and no carbon.
This was very plain on a section that was cut through with no crane and japped.
They filmed it and you could see the spark jumping around..
Now why cant I get insurance on my carbon mast now that it is over 10 years old???????

[powerabout]

another lightening story
I also have an old J24 that had a direct hit when moored (before I bought it)and the lightening exited the hull in about 5 places as in it blew holes you could put your fist through from the front to aft the aft bulkhead.
These were all the places the core was wet!
It sank fast right in front of the club in the middle of the day with everyone watching

[peter radclyffe]

alden, herreshoff, fife, archer, trumpy, nicholson, mylne, watson, stephens, abeking, fox, nevin, fay, just a few builders who are designers, & engineers

[Fanie]

Coyote is actually a Freedom 40 monohull, not that that makes any difference

Actually I think you hit the nail on the head there

Lightning is unpredictable. If it wasn't a carbon mast the outcome may or may not have been the same. Very few things can withstand a direct lightning strike, from huge trees that gets burned out completely in a split second, to part of buildings that gets disintigrated to yes, even boats.

It is still my opinion that it is very unlikely that the boat got hit because the mast was carbon specifically. If you fly at cloud level and you look down it is hard to make out high(ish) buildings or towers, never mind a boat's mast, so it has to be random and unfortunate. If the boat was any distance away from that exact spot it may not have been hit at all.

[Chris Ostlind]

Fanie,

I do like the business of ascribing a seeing function to lightning. I'm also not in the camp, as you suggest it.

If it were a seeing thing from Thor's lofty place, then how in the devil does the lightning regularly see the very tiny compared to a building, well-earthed lightning rods so affixed?

Could it be that the charge is simply seeking ground by a random path of least resistance?

I've been in several high altitude electrical storms while mountaineering and have seen a strike hit boulders nearby, while the climbing team was groveling with a full array of metal hardware, our hair standing on end and the most lovely smell in the atmosphere. We found out later that the lightning strike was directly on a surveying marker with a long iron rod driven into the mountain top to hold it in place.

Just lucky that we weren't any closer, but that juice knew where to go.

[Fanie]

Hi Chris,

then how in the devil does the lightning regularly see the very tiny compared to a building, well-earthed lightning rods so affixed?

If you look at grass roof houses they plant those masts with a thin sharp spike and ground loop around it. Most think it is to 'draw' lightning to it, but the fist function of those thin spikes, which clearly cannot carry a lightning bolt's power, is to dicharge the environment, secondly to actually reduce the chances of the lightning hitting the thatch roof, hence preventing a fire.

Friction in the air and where clouds are per se' causes huge static offsets wrt the earth and when it discharges it goes to the nearest point of opposite potential. Those sharp spiks are supposed to discharge the environment. A blunt pole won't do the same, or to a much lesser effect.

If you have a good ground, usually a rocky outcrop that is rich in metal deposit the lighning will hit the same place over and over. I know someone who'se house is on such a place, the lightning gets them time and again. They have now put up some poles for the lighting to conduct through and it helps to some extent.

As I said, lighting is unpredictable. If it was we could just identify it's behaviour and contain it with sufficient lighting conduction.

In the case of Coyote (the Freedom 40 monohull) I'm sure it must have been around lighting before, as have many boats with masts, but they are not seeked out deliberately, or we would have a disaster eash time there's a storm.

[Chris Ostlind]

Hi Fanie,

Regretfully, I'm afraid that you have misunderestimated the complex Scandinavian personality of Thor.

;-) ;-) ;-)

[Fanie]

Possibly and probably. He won't ask where to put his next...

[bruceb]

In the early 1980s, hobie switched the top of their masts (about 8') to carbon/glass composite for safety from overhead power lines. The halyard was changed to rope, so there is no electrical path on the mast. After the change over, boats seemed to be struck by lightning while sitting on the beach or moored to a dock. (I never was aware of one being struck while in use) The composite section usually exploded, with minimal damage below it. Just an observation, but the damage was impressive, and I never saw it happen to a solid metal mast. Bruce

[Stumble]

I am wondering if this question stems from in interest in what happens if a carbon mast is struck, or if it would be better to have a carbon mast vs an aluminum one.

From a practical standpoint I don't think it really matters what material the mast is since you are still going to have all sorts of electrical antenna up the rig providing a nice metal pathway to the rest of the boat. Which is going to result in some sort of significant structual damage (I have seen seacocks blown out, keel bolts melted, engine shafts kicked out of the hull...). So from that perspective I think the real problem you face is exacally how large are the bilge pumps, assuming you still have some way to power them now that a good portion of your electrical system is fried.

[Fanie]

I think the 'size' of the lighning must have a big effect in the misfortune of a direct hit. A huge bolt may melt even the alu mast, and disintegrate a carbon mast. Even a non conductive mast is at risk ie a fiberglass or wooden mast. Remember there are wiring going to the top of the mast, I doubt the lighting is going to exemp the wiring just because it is thinner than the alu mast It will still take the shortest path it can.

I got hit by lighting once in the '80's, through the telephone when the lighting hit the next door building so it was an indirect hit for me. Very unpleasant to say the least. I was out as a candle, dunno for how long. The building next door's alu aerial was melted and all elctronics in it fried.