Carbon Fiber & Lightening

[Ronbye]

I just finished watching a program about a SuperPuma helicopter which was ferrying workers to a offshore oil rig in the North Sea. They never made it as they were struck by lightening and the tail rotor let go which resulted in a ditching in Force 10 weather. All 16 passengers and 2 pilots were successfully rescued and nobody was hurt. The investigators from the Civil Aviation Authority in Britain had determined that the tail rotor blades that were originally made from fiberglass were now being made from carbon fiber. They quite unexpectantly discovered that carbon fiber is a greater conductor of electricity than fiberglass by as much as 1000 times. In this case, the rotors while operating in a storm cloud generated enough static electricity to cause a lightening strike which was concentrated at the tail rotor and it exploded causing the crash.

With the ever increasing use of carbon fiber for masts, I think a warning should go out to those owners of boats with carbon fiber masts to ensure that their rigs are protected against lightening. Particularly for those folks who live in areas that are prone to lightening.

I would also like to see some discussion on this from the experts in carbon fiber construction and lightening science. Somebody's life may very depend on the knowledge glean from this. It was definetly an eye opener for me.

[SailorMitch]

Ron -- Chances are, folks with carbon fiber masts are well aware of the lightening risk. For a couple of years I lurked on the Freedom Yachts email list here on Sailnet and saw a couple of stories about people losing masts due to lightening. Unfortunately, one guy bought a boat with what he was told were cosmetic cracks in his mast -- only to lose the rig later on in fairly benign conditions. Turned out the mast had been struck by lightening at some point but it was very hard to detect.

Next, what about aluminum masts and lightening....? Any better than carbon fiber? When I'm out in a storm I always feel like a target with that 47 foot tall hunk of metal sticking into the air. Oh well.

[gc1111]

There are some small racing boats (e.g. Hobie cats) that allow carbon fiber usage in the masts. At every regatta (and other places) there are major warnings about power lines and carbon fiber masts. So I think lots of people are aware of the problem. Whether or not they respond appropriately is another matter :-)

[sailingdog]

The real problem with Carbon Fiber masts is that the resin does not conduct electricity well, while the carbon fiber does... so the heat from the resistance often causes the laminate to delaminate. However, since the damage is often internal to the laminate, it doesn't appear to be significantly damaged and then fails catastrophically, with little or no warning.

[Bob1112]

Somebody told me once that knowledgeable insurers will not cover lightning strikes to carbon masts. If true, this is really important, since depending upon the boat a replacement spar can run upwards of $20,000 or more.

[SailorMitch]

Dog -- Thanks. That really describes what happened to that one fellow with the Freedom. It also makes sense from a conductivity viewpoint, and why an aluminum mast likely will come through a strike unscathed. The metal is a solid conductor and will let the electrical charge follow the grounding path to the keel-- hopefully? From what I have read and observed, these strikes are so powerful that the electricity pretty much goes where it wants, follows whatever path it wants, etc.

[sailaway21]

Jones2r hit on a good point. IMHO, if you are worried about lightning strikes as a terminater to your sailing experience you might wish to select a different leisure-time activity. Most all of the "evidence" is anecdotal and barely into the theory category. I'd probably ground my mast and sail on worry free. It's not the type of situation, in a severe strike, you are going to walk away from anyway. In my career on ships I was never struck and our masts were substantially higher than any boats. I could be way off on this-lightning strikes happen all the time-but how often do they hit something of value? After twenty years at sea, I just found out I was suppossed to be worried about lightning-oh wow!

[paul949]

For well over one hundred years the lighting rod has been protecting boats and land based structures from lighting.

You folks need to read up on lighting protection

Paul Marine Engineering Costa Mesa California

[sailingdog]

For lightning grounding/bonding on a boat with a carbon fiber mast, you need to run some seriously heavy cable up the mast. On a boat with an aluminum mast, you can often just use the mast.

[sailaway21]

And for over a hundred years nobodies been able to figure out if they really work or not!
Farmers don't seem to think so as they've stopped putting them on their barns, but YMMV.