Carbon masts and lightning

[51jay]

Doesn't lightning actually travel the other way ground or water to sky

 

[powerabout]

correct ( ish I think the bolt comes down to meet the riser then it goes back up in section each meeting one coming down and so on)
I have been jolted ( about as bad as holding a spark plug) several times

Walking up the boat ramp holding the rear beam of a beach cat during an approaching lightening storm ( not smart) and obviously i was being lined up as the conductor from ground to beam to mast, got shock dropped boat just as lightening hit the ground closeby.
Got another one, jumped off the Mumm 30 ( carbo stick) and held the stern rail as we reversed into a marina pen, same story got the jolt and then the lightening hit somewhere else.
I have seen a Discovery where the 'risers' have been filmed going up from all objects in a small area including a guys head, he was unaware and the lightening hit the ground a couple of hundred yards away.

When it comes to yachts the tallest object never gets struck. I wonder if its the well grounded mast that gets hit as it shows the best best path for the riser?

 

[Eric Sponberg]

Being an enthusiast of carbon fiber masts, I collect stories of lightning strikes on them. I have seen carbon masts turn to toast, and I have seen them survive. Those that get toasted are the ones with no lightning ground wire inside the mast. The easiest path for the lightning is through the mast laminate itself which is electrically conductive, being carbon. The fibers and the resin burn out, rendering the mast totally useless and unrepairable. Those that survive usually have a lightning ground wire inside the mast. The ground wire is an easier path for the lightning, having a lower resistance than the laminate. In these cases, the mast suffers no damage and goes on to sail another day.

I definitely recommend having a ground wire inside the mast and connected to an air terminal (solid round rod with a spherical top end) at the top of the mast and also to a grounding plate on the outside of the hull below the waterline.

Eric

 

[marshmat]

Good point about the ground wire, Eric. Ever since this became standard practice on office towers and other large buildings, we see them get hit fairly often, but almost never damaged.

If I'm not mistaken, that external grounding plate is supposed to be right below the mast step, otherwise the lightning may balk at having to turn sideways and will just go straight through the hull anyway. Sound right?

 

[Eric Sponberg]

Thanks Matt.

Yes, the ground plate in any boat should be near to the mast, and the ground wire should not have any sharp bends in it. The ground wire should have as straight a path as possible with good solid bolted connections.

Eric

 

[Chris Ostlind]

Hey Eric,

Do you have any suggestions on the lack of right angle pathways, then, for carbon masted catamarans?

Is the best route the, mast to forward beam, to hull and away, the most successful solution, even though it incorporates two right angles in its route?

Perhaps a suspended, immersed ground bar, hanging from the forward beam, is a better solution? Not so elegant, but maybe the best overall for a cruising craft?

 

[Richard Woods]

"Perhaps a suspended, immersed ground bar, hanging from the forward beam, is a better solution? Not so elegant, but maybe the best overall for a cruising craft?"

That is exactly what I have been using since being struck by lightning on my Eclipse back in 2003

I use one supplied by Strikeshield.com. I haven't been hit since fitting it, even though boats close by (ie 20yds) have.

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

[nero]

"Those that survive usually have a lightning ground wire inside the mast"

Does the ground wire have to be on the inside of the mast?

Regards

 

[Luckless]

I definitely recommend having a ground wire inside the mast and connected to an air terminal (solid round rod with a spherical top end) at the top of the mast and also to a grounding plate on the outside of the hull below the waterline.

Eric

Why would you want a spherical top end? It has been a few years since my last physics lecture, but from what I remember a pointed spike will bleed off charge easier than a blunt ball. Lightening works as a transfer of charge and lightening rods causes an area to become more neutral in charge so when lightening forms it is encouraged to take another path along a higher charge difference. A rounded ball should, in theory, encourage strikes.



As for the material the mast is made of, just think about it. We're talking about energy that has just had the ability to make a spark jump a few thousand feet long. It doesn't really matter what material it is made of, if it happens to influence the charge field enough then it will 'conduct' a lightening bolt.

 

[bruceb]

Grounds

I have inspected and/or repaired about two dozen lighting damaged boats, and everything I observed would agree with installing a ground plate and wire system. It doesn't stop every strike, some of the most damaged boats have been on dock shore power systems that were struck, then discharging through several boats and all their attached equipment. I used to race small trailer sailors that had no ground system or keel to ground too. I used to drag a set of copper jumper cables and clamp them to a shroud in afternoon thunder storms- I once saw lighting strike the water about a boat length away but I was not hit. I was scared! It gets your attention. The problem with dragging something is knowing when to put it in, some of the worst strikes come before a storm. I have wondered about the effectiveness of a ground plate in a centerboard/dagger board trunk? Anybody have an opinion? Bruce