Lightning strike scare???

[Sloop John B]

I think what we most fear is a strike on our mast that comes down through the cockpit, through that metal post along side the table that the center board pennet runs, and just as you're about to take your first sip of a glass of Michelob Bock beer, a side flash bursts into your upper thoracic region and boils your brain and starts all your hair on fire. No?

Hey, come on down to Florida, thunderstorm/hurricane season is just starting.

[zuma hans 1]

I honestly don't know much about lightning, but It seems to me that the dissipators make a lot of sense as you've indicated. I can't understand how the grounding would make it more attractive once it was grounded? Wouldn't the difference in charge be negligible at that point? I noticed with my boat before I added the cables that the charge would build up over a few seconds, and then I'd get shoked , and dischare with my aluminum boat hook. Since the cable is always in the water, the charge never builds up? Comments?

There's always a debate about this.

I used to work at an AM radio station under a big tower. During a lightning storm, we would watch the insulated sections of guy wires build up a charge from the atmosphere until they would arc.

That's exactly what your boat is doing in a lightning-charged atmosphere. The boat is slowly becoming more charged like the sky.

One side of the argument says that's good, you want to be as unattractive to a sudden discharge from above as possible. A sudden discharge from your boat to the water is inconsequential.

From the viewpoint of a lightning charge, grounding serves as the easiest path to discharge into the ground. Electricity will always seek the easiest path, and by grounding your boat, you are giving those electrons in the sky a freeway to the ground, right thru your boat.

The other side of the argument says you want to constantly attenuate the boat by grounding it. The sudden discharge from the boat to the water, this argument goes, opens a circuit into the ground for the sky's buildup to exploit.

My opinion is to get away from a boat in such a circumstance as fast as possible, if it is possible. Of course this won't work on the high seas, like you were out in the sound.

Last time I was in a boat in a lightning storm, on Lake Powell, I had a few minutes to prepare. I beached, anchored, and sent the kids down the beach to get away from the mast. We sat on the sand in a low spot and waited in the rain for it to pass.

[Dimitri-2000X-Tampa]

Not sure I would agree that it is safer to be out on the beach than inside the cabin (staying away from mast compression post). My gut feel is that lightning hits objects on the ground more often than floating objects in the water (such as boats). I have watched lightning hit a (grounded) channel marker as I windsurfed about 50 feet away from it once (don't ask). In one of our other long winded discussions on this, I think there was a general consensus that you would still be safer in a sailboat cabin with a mast sticking out than you might be in an open powerboat with no cabin. Of course, these sorts of things are near impossible to prove.

[Harrison]

Yes, there are very long discussions about various lightning techniques, and Im sure we all can agree that lightning will do what it wants to, when it wants to. What Id like to see is different methods of remedying the unexpected charges that build up on our boats. So far the only remedy Ive been told about (Thank you Richard OBrien), is to ground the shrouds to the water. Simply connecting a piece of wire to the shroud, and dropping the other end into the water seems to be a quick fix. Again, Im not trying to direct a lightnings path, Im just to keep my boat from constantly shocking me while I do my damdest (sp?) to get off the water. For those of you who have never expirenced this constant shocking, it really is a feat, to get you off the water without a zap! Next time your out and you have to return due to bad weather, just look around at how much metal you have thats waiting for you to touch it, and zap you.

I just purchased a static wick similar to the one mention earlier in the thread by Hammin X. I was a little disappointed as the instructions call for it to be grounded to the water. Im already doing that!

Im going to mount the wick to my mast top and wait and see if it alone WITHOUT grounding, will eliminate or reduce the charges building up on my boat. Ill post when I know more.

---Harrison

[Richard O'Brien]

Yea Harrison. It's just a fix to get your boat off the water. the guy from NOAA Who lectured about lightning in May said "the best thing to do is snuggle up next to the tallest mast in the Marina.

[craiglaforce]

Rich,

THe thing you are missing is that before a strike, a vertical electric field gradient develops that is something like 10,000 volts per foot of vertical air distance.

If the mast is grounded to the water, electrons are pulled up the mast from the water's endless supply, through the grounding cable, and develop HUGE voltage potential at the top of the mast. This is what attracts the lightning. THe brush dissipator devices, are designed to release at least some of this charge via ionized air streamers from its points.

Not sure of an analogy to illustrate but how about this?

An ungrounded mast is like a bridge for the lightning to cross some distance.

A grounded mast is like a bridge with a conveyor belt, neon lights, beer and strippers on the end.

A person might cross either bridge, but realistically the odds of the 2nd bridge getting used are a lot greater.

[Richard O'Brien]

Like the "Vegas-like" analogy Craig If yoyu don't ground the mast here in our area, the rigging acts like a giant capacitor connected to the storm above. that makes it a very short distance to the water , 2'-3'. Wouldn't that be just as dangerous? Both Harrison and I have experienced the crackling sound in the rigging , and the sharp 1" or more shocks when you get near the rigging. These aren't your garden variety carpet shocks. They really hurt. Benjamin Franklin wasn't grounded. Comments?

[Hamin' X]

There are two basic theories for lightning protection.

1.) Give the lightning a good path to ground, so that it will dissipate itself harmlessly.

2.) Make the object unattractive to lightning, so that it will not be struck in the first place.

Number one works very well, if you have an excellent ground, with large enough conductors and perfect connections. In the real world, these conditions are difficult to achieve and even more difficult to maintain. The result of even a fraction of an Ohm of resistance in a connection, at the voltage and amperage of lightning, will be transient voltages and fried electronics. Your rigging could be burned at a weak point, with the possibility of a de-masting during a high wind event, the result.

Number two works almost as well as number one, under ideal conditions for number one. However, in the real world, number two is much more effective. It prevents the positive charge from reaching a strike potential by dissipating the excess electrons to the atmosphere before they reach a high enough state to attract the lightning strike. There is no need to ground the boat, as the charge is dissipated to the air, and grounding will only increase the flow of free electrons to the dissipator.

Aircraft have used this method for years, with great success. Even with no ground available in flight, they are shedding the excess electrons gathered from air passing over the airframe.

Hope this helps to explain the theory some.

Rich

[Highlander]

Chris

I was 12 miles out when this blew up last year in Georgian bay Ont. winds dropped dead to nothing dropped the sails then shot this & motored to Meaford Harbour in a following swell of 8-12 ft that was a ride . Rode it south east had fun getting into the harbour around midnight in 20nkt winds had a crowd watching me & helped me dock harbour master told me they registered 52mph winds pretty well most of the night . was so noisy & loud all night just sat up & watched dvd movies all night with a few scotch's of course guy accross the dock from me in a 35ft sail boat said he got tossed out his bunk 3 times & then moved to a lower berth was a few damaged boats the next morning . the movie is more dramatic to watch in the dark

John

[Dimitri-2000X-Tampa]

I couldn't get that movie to play.

[Highlander]

Dimitri

Try again I reposted it & it worked for me now

John

[waternwaves]

For those that are interested how we in the US have developed some of our principles and practices of lighting protection.

some of the references are to British navy practices also.

along with current (no pun intended) research.

(for those of you who wonder where NFPA 780 came from)

Tho, if anchored, an anchor chain to mast connection starts to look plausible.

[Bransher]

I found the following to be interesting. A couple of years ago, I was awakened at my house one night by what appeared to be another summer thunderstorm which are very common in Florida. This time, however, there was something different about it. There was intense and continuous lightning directly overhead, but no thunder could be heard. The lightning was so nonstop that it almost appeared like daylight outside. But as I said, there was silence until that unmistakable freight train sound was heard. It was a large tornado that passed within about 2 miles of my house. I was fortunate, but more than a dozen died that night and there was much property damage. I assume that the sound of the thunder was carried aloft in the vortex of the tornado.

[Mikebe]

I'm not an expert on lightning, but I have a background in electrical engineering. Seems to me the main difference between an aluminum mast and a lightning rod is the lightning rod is grounded. IIRC lightning rods are known to actually attract lightning.

So, I'm not planning to do anything that converts my mast into a giant lightning rod. The best thing is to try to avoid getting hit, because if you take a hit it's probably going to be a very bad day, whether the mast is grounded or not.

[Moe]

Your electrical system negative bus is already grounded if you have an outboard. Even if it's tilted out of the water, the mount is probably still in, as is an anode on it. Besides the electrical system, the steering and shifting system are grounded through the outboard. If your mast plug is connected, that grounded wire extends up to the factory steaming light, or to an anchor light. If you have an end-fed VHF whip antenna at the mast top, the whip antenna is DC coupled to the shield at the base, which is bonded to the top of the mast, which is then grounded through the radio to the electrical system to the outboard. Measure it with an ohmmeter if you don't believe that.

On the 26X, the poorly conducting stainless steel compression post is bonded to the mast bottom, but not to the centerboard hanger bolt and I wouldn't bond it there. At the mast base, there's a factory supplied rat's nest of electrical wiring. Don't know about the M, but I suspect there's also wiring there.

I'm not an EE, but I don't buy the grounding supplies an unlimited charge of electrons theory. The strike leader coming from the cloud is negatively charged and repels electrons away from it, both air it travels down, creating an ionized channel, and on the ground surface as well as objects on the ground. An attachment spark coming towards the strike leader from below should be positively charged ions, ie cations, which can come from objects grounded or not. As I understand it, the thinner a single point object at the top, i.e. lightning rod profile, the potentially longer the attachment spark. The more and wider multiple points at the top, i.e. the brush, the shorter the attachment spark. The former don't guarantee a strike, and the later don't guarantee prevention of it.

The mast and shrouds should develop a charge, positive on top, negative on the bottom, where excess free electrons can begin sparking off and creating ionized paths between themselves and objects at a relatively positive charge, potential paths for side strikes after a strike to the mast. Bonding of metal throughout the boat should help prevent side strikes.

Grounding the mast and shrouds should give those excess free electrons a place to go, not come from, and reduce the chance of getting shocked by them, pre-strike. Those here who've tried it have experienced just that.

Ewen Thomas's research, which included analysis of insurance claims, disproved the hypothesis grounding increased the chance of being hit.

Now all this being said, I've neither grounded or bonded, for a several reasons. One, I firmly believe when it's your time to go, you're gonna go, regardless of what you do to try to stop that. Two, where, on a small boat, do you try to route lightning, as if anything you do would have any certainty of having any influence on it? Finally, we're in fresh water, where a decent interface between a grounding system and the water is an almost impossible task.

--
Moe