Carbon Fiber & Lightening

[LazyGuy]

If you ask three experts about lightening, you will get at least 4 different answers. The bottom line is that there is a lot of conflicting evidence about lightening. If you bond your boat, you attract lightening, if you don't do anything, you do not attract it. So the best option is to not do anything and stay "near" a bonded boat.

It never occurred to me that a carbon fiber mast is like a spark plug wire. Resin replaces the rubber cover and it is filled with carbon. Adding a huge copper conductor inside the mast to carry the lightning current to ground defeats the purpose of using CF by adding weight high in the boat.

Maybe one of the problems is CF with wire rigging. If you have a CF mast and non metal rigging, I would think that the lightening would not be attracted to the rig? That would only leave a problem when you are miles from nowhere which is when it does not matter what you do. Just an opinion.

Cheers
Dennis

[Goodnewsboy]

Lightning protection systems (Lightning rods) are alive and well.

Shortly after I built my present home, we suffered two direct hits within a month. We (very quickly) contacted a lightning rod installer and had a UL master label system installed.

Since that time (Over 25 years) our buildings have not been struck again, even though we have had near misses as close as about 50 feet away.

As for the notion that nobody installs lightning protection anymore, you should look somewhat closer and you will find that the systems are still there, but perhaps don't look the same. Check out your local broadcast tower (Radio, TV, or cell phone) and you will find that lightning protection is built in.

[Insails]

From a meteorological stand point to me it don't matter..Lightning is what lightning is..
It will happen in a series of strokes..first a channel from the cloud to your mast(leader stroke),then you have a return stroke(return streamer) up the channel from the mast(this is the bright flash you see)..

Aluminum would transfer the load and heat better and more efficiently than carbon fiber...

I can see where the heat from lightning could delaminate carbon fiber...

no matter what mast you have you are the tallest object..

thats the ODDS that matter!

[deckhanddave]

sailingdog summed it up in a nutshell. Carbon conducts (though poorly compared to aluminum) while resin is an insulator. As a result you have extreme temperature differences that causes severe expansion and contraction at dissimilar rates. Its almost the same thing as distressing a fiberglass laminate. The glass separates away from resin bonds and you hare left with loose threads of glass. If I remember correctly the list goes: When it comes to lightning, wood explodes, carbon splinters, and aluminum conducts to ground. The problem then is the ground...

Anyone try out those funky bottle brush things that are supposed to "dissapate" the earth born lead charge to prevent a strike?

[sailingdog]

Those funky bottle brush things only work if the boat is properly grounded...otherwise, they're not doing anything. BTW, a grounded/bonded boat is more likely to get hit than an ungrounded boat, but the damage on an ungrounded/unbonded boat is generally more expensive to repair. It's basically a crap shoot... six of one, half-dozen of the other... higher risk of getting hit/lower risk of catastrophic damage... or lower risk of getting hit/higher risk of catastrophic damage.

[Ronbye]

This thread has generated a lot of discussion. As we don't get very much lightening here, I would say that there are very few boats in my area that are grounded. Saying that, I carry a long set of heavy gauge booster cables on board. If there is a threat of severe lightening I will clip one end on the bottom of the mast and throw the other end in the water. So far so good. If I am docked, I will dissconnect the electronics which is fairly easy for me to do.

[LazyGuy]

Ronbye,

I am assuming you have a deck stepped mast. In my "I am an electrical engineer but certainly not a lightening expert" opinion, you may be doing exactly the wrong thing. The bolt of energy is trying to find the path of least resistance to ground. You are placing your mast top at ground potential (water) which may attract lightening but if it is a direct hit, the energy from the lightening will not make the 90% turn at the bottom of the mast to head for the water. Instead it may burn the cabin top or end up arcing from mast to keel burning everything in between. It is difficult to fathom the amount of energy contained in a lightening bolt.

Just an opinion.

Dennis

[Goodnewsboy]

Maybe I have it backwards, but it has seemed from long experience with lightning rods at my home (27 years with no lightning strikes) that their function is to drain static charge off into the air and thereby to equalize potential differences that might otherwise attract a hit. From what I have been able to learn, the rods and connections are not intended to attract lightning, although they are sized to do so.

It would seem that an important element in obtaining such protection is a low resistance conductor that is continuous from masthead to seawater, just as it is important to have and maintain effective ground rods in the earth around structures that have lightning rods.

The principal problem with lightning protection in a vessel is the great difficulty of providing an effective connection to the water. Ground plates are deemed inadequate unless they have tremendous surface area, and external keels are often coated with material that is not helpful. Add to that the fact that the key hull to water interface seems to be at the waterline, and you get the idea that it isn't quite as simple as connecting a bond wire to a keelbolt.

Incidentally, it seems that lightning is a greater problem for boats in fresh water. That is probably because it is a less efficient electrolyte than seawater and therefore impedes the free flow of static charges.

[Wayne25]

May I suggest the following site to learn about lightning:
http://www.strikeshield.com/
And perhaps this one although some of it is dated:
http://www.thomson.ece.ufl.edu/lightning/

To pick out the good points made so far:
• The angle from the mast to the ground terminal is important. Keep the angle as slight as possible.
• Lightning passes from the ground terminal to the water through the edges not the surface of the plate if that’s what you are using. The reason fresh water boats suffer more damage is because fresh water is less conductive than salt water and you need more edge area to compensate. Most fresh water boats don’t compensate and it’s a big difference.
• If you don’t ground your mast, data shows you only have a slightly less chance of being struck. However, your chances of damage are much higher, not to mention the added risk to you and your crew from branches of the lightning trying to find a ground. An ungrounded or improperly grounded boat will suffer holes at the waterline from the lightning.
• You need a large good conductor to your ground terminal. The bulk of the current actually goes around the surface of the conductor.
• It’s correct that the “brush” dissipaters need a good ground also. However, the effective area they have isn’t enough to discharge the static build up experienced during a strike. Not enough data yet to determine if they can bleed off enough charge to stop some or any strikes. Most are installed incorrectly to a ground terminal, so the data is bad.

Wayne

[wbrakman]

so, if i have a freestanding cf mast, do i run a 2/0 gage battery cable up the mast to the mast crane, or is the standard awg 8 good enough?

Hank