Being Hit By Lightning - To Ground or Not

[sailingdog]

GBurton-

In all the studies of lightning, it generally takes the shortest path to ground... that is straight down the mast... The contact between the jumper cable clamps and the rigging is miniscule compared to that provided by the entire mast, especially if the mast is keel stepped and connected to the keel bolts. Even in the case of a deck-stepped mast, the mast is still the most likely strike conductor, unless it is a wooden or carbon fiber mast.

[sailingdog]

If your keel is lead and not encapsulated in fiberglass, you could sink a copper bolt into it and then put a copper plate on the bottom of it... and the keel would act as a conductor to the grounding plate. Then again, this might even work for an encapsulated lead keel, provided the lead is one giant chunk, and not lead shot or something like that.

Originally Posted by Stillraining

Advice by some people with a hole lot more experience them I.

I'm taking it all in !!

Now for my individual case please refer to post # 10 for pictures.

1) I have sofar gathered not to try and redirect the strike horizonally to my existing bonding plate. Ok I got that

2) My fuel tanks straddle the mast step ( Built in fiberglass at construction ) and my keel bolts are SS a very poor conductor Im finding out here.

3) There is no room for any new hull penitrations due to fuel tanks and keel. ( unless drilled all the way thru keel ..yikes!!

4) Lightning current will flow to the bottom of the mast possibally causing severe side flashes befor returnning up mast to posibally disipate thru another mast conected channel. ie..shroud or mast deck to water connection.

Im stuck on what to do on this one guys ?

[GBurton]

You're assuming that the hit is going to happen on the mast...

If the mast is deck stepped, without a bonding conducter - now what?
The energy has to go somewhere.

Originally Posted by sailingdog

GBurton-

In all the studies of lightning, it generally takes the shortest path to ground... that is straight down the mast... The contact between the jumper cable clamps and the rigging is miniscule compared to that provided by the entire mast, especially if the mast is keel stepped and connected to the keel bolts. Even in the case of a deck-stepped mast, the mast is still the most likely strike conductor, unless it is a wooden or carbon fiber mast.

[sailingdog]

Most deck-stepped masts have a compression post of some sort below them, which is often metal, and usually connected to the mast step itself via several bolts.

[GBurton]

Some do but many do not.

The jumper cables could help - please think before you post.

[LarryandSusanMacDonald]

I've been on a number of lists with threads on lightning. They all boiled down to the two schools of thought mentioned above - ground and hope the 20 gazillion volts goes down that little wire and discharges into the water or don't ground and hope it's attracted to something else.

I've worked in the marine industry for a dozen years, I've lived aboard for those same dozen years. We've cruised all around and I've met many people who have been hit by lightning. In each case, also being a lightning -phobe, I've asked many questions. It actually boils down to this: It's a crap-shoot. Ground and you can get hit just as easily as you can get hit by not grounding.

A few anecdotes: a sport fish charter boat at the City Marina in Ft. Pierce, Florida was hit on three different occasions. At the dock, next to other boats. What was different? Nothing anybody could figure. Just serious anti-serendipity.

A very good live-aboard friend of mine on a 41' 1941 Rhodes (wooden, obviously) sat between two glass boats at the dock. Both had metal masts. The Rhodes had a wooden mast. The metal masts were both taller, one significantly. The Rhodes had one of those static dissipator gadgets and was grounded. During a violent lightning storm, my friend's boat got hit. My boat was about 50 yards away and both my wife and I could feel our hair stand on end just before the hit. The noise was incredible. My friend said they hardly heard a thing. It scarred the mast, and the electromagnetic discharge took out a lot of his electronics. No other harm done. Interestingly, one of the boats next to him was moved to a different slip and it was hit a few weeks later. Maybe the strike which hit my friend's boat was aiming at the boat next to his. Who knows?

Another strange one: a Hunter on Lake Erie was hit. A relatively new boat. The lightning dissipated through the hull above the water line leaving scores, if not hundreds of tiny pin-holes. My guess was uncured pockets of resin superheated. Strictly a guess.

My opinion? Since it is a crap shoot, I opt for not grounding. Grounding - especially bonding - causes (rather than prevents) electrolysis. Another argument, I know, but I have seen it way too many times - corroded through-hulls are bonded through-hulls. It makes sense to me, you've got a battery and you've essentially turned it on by connecting all of your anodes together, raising the potential.

I am told that you have less of a chance of getting hit while under sail than at a dock. That may be true - I've never met anyone who has been hit while sailing - but it also may be that boats spend more time at the dock than sailing (unfortunately). So if a boat is going to get hit at any given time, odds are it's going to be at the dock.

Cap'n Larry and Saltwater Suzi

[sailingdog]

Gburton-

Using the jumper cables is far more likely to give someone a false sense of security than it is to actually help. There are far too many variables to really say for certainty. It depends on whether the boat is deck-stepped or keel stepped, whether it has a metal or a wooden compression post, whether the keel is encapsulated or not, etc.

However, in the overall scheme of things, jumper cables are far more likely to cause sideflashes or do nothing than to actually reduce the risk of getting hit. That's been pretty well proven by what studies are out there. You might want to take your own advice and not post a technique, which at best is going to give a person a false sense of security and possibly prevent them from taking effective measures.

Originally Posted by GBurton

Some do but many do not.

The jumper cables could help - please think before you post.

[Wayne25]

I don't really have a good grounding path from my deck stepped mast to the exterior of my hull. So I bought 10' of heavy tinned marine battery cable with a 3/8" watertight lug on both ends. I connect it 6' up the mast using a metal slug stop in the mast groove ( the kind with a stud and thumb nut) and to a very well ribbed zinc (the kind used on a large Yammy that gives many feet of linear edge exposure) and drop the zinc in the water. This produces a direct path to a very good ground at a very slight angle. it is very easy to set up. I use it when at dock or when there is a storm at anchor. I can also use while underway if I'm caught out in a storm. Seems to be the best solution for me. It also keeps the grounding outside of the cabin.

[GBurton]

How would jumper cables cause a sideflash? If they were not there its possible the chainplates could be the sideflash point.

Do try to keep up.

[Stillraining]

encapsulated. I do not know about the ballest I will try to find out. Could it be iron? Very hard to drill if so.

Great idea though!!

Now you guys got me thinking about my mitzen mast also which is deck steped mad our bed is right under it!!. I figured the cone of protection would protect it but now this discussion has me doubting that.