Lightning protection options

[mike]

I've been doing much reading regarding lightning strikes. Of course, I recognize that the best solution is to avoid bad weather in the first place, but if I find myself out on the open water with a storm approaching, and am unable to outrun it, I'd sure like to have some way to channel a strike to the water.

An "old salt" I spoke to a few months ago who sails a 25' Catalina said he carries some jumper cables with him, clamps one end to his rigging, and tosses the other end in the water when he fears a thunderstorm is on the way. I would think this wouldn't provide nearly enough grounding area in the water, but I sure do like the idea of a detachable system like this.

If I were to improve on it by adding an appropriately sized grounding plate to the water end of the cables, would this provide a good deploy-when-needed solution?

Obviously there's an added risk that increases dramatically as the storm gets nearer... I wouldn't want to be in the middle of handling this thing when lightning hits! So, it would have to be deployed early enough to minimize this risk.

--Mike

[Chip Hindes]

This is a problem with the current discussion board, with stuff falling off as it gets old. There was a monster discussion on this exact subject about two months ago. There was so much disagreement about what to do and what not to do, I hesitate to provide even a partial answer.

There was, I believe, general agreement that the jumper cable solution you described is, at best, inadequate.

The disagreement could be summarized as follows: Some "experts" say such a solution actually increases the likelyhood of a strike, while doing almost nothing to dissipate it. Others "experts" stated that grounding does not increase the likelyhood of a strike.

I have an article on the subject from a Sail Magazine of about 18 months ago, scanned to pdf. I can email it to you if you contact me and provide your email address.

[craiglaforce]

Wow, I didn't realize that the old posts go away after a while.
I just tried a search on LIghtning and Arlyn stewart and got no matches.

Arlyn Stewart has a good website where he has an excellent discussion of lightning theory.


http://www.stewartfam.net/arlyn/lightning2.html

[ken lockhart]

Mike, back when I owned a 26X, I tok heavy duty cable and conected it to the chainplates inside the hul. The bolts are long enough that you can attach the conectors by just adding another nut to the bolt, I then attached them to the center board trunk metal the same way. I figured this would help shunt some of the strike to the water without jumping around in the cabin or on deck. I also cary two bat. cables with a one sq ft piece of copper welded to each one. I then attach them to the side stays just like the old salt. It makes me fel beter in a storm.
I had a boat that got strck at the dock one summer. The lightning jumped around inside the boat and hit a spinnaker pole I had layed on the bunk and exited at the end that was up against the hull at the water line. I just don't want to be the shunt for the strike to find it's way to the water.

[Jack O'Brien]

The Arlyn Stewart site is excellent reading. See also:

http://www.thomson.ece.ufl.edu/lightning/

[Jack O'Brien]

http://www.sailnet.com/collections/arti ... %20&tfr=fp

[Frank C]

I would have posted the Sailnet link to Don Casey's article, but Jack did so just above. It is definitely worthwhile reading.

Can't promise you it's "accurate" because there's no agreement on this subject, but I will say that Casey's article is the most lucid and succinct description of lightning protection that I've ever read. He debunks the use of porcupine diffusers in a single, believable phrase.

Dissipaters probably do bleed off static charges, but trying to bleed the ocean's charge into the air with a dissipater on your mast is like trying to lower the ocean's level with a soda straw.

California is at near-zero risk from lightning, or I'd be following his recommendations.

[Andy26M]

I think the key thing to absorb from these articles is the fact that the charge dissipates from the edges of the grounding plate, and that the plate needs to have a minimum total "edge length" to be effective - roughly six times as much in fresh water as in salt water, depending on how "pure" the fresh water is.

Taking all that into consideration, a "portable" system should work for our Macs with no installed ground plate. You'd need a good, solid connection at the base of the mast to which you'd bolt, not clamp, a heavy conductive cable, the length of cable reaching the water, and bolted (welded?) to a piece of solid copper with the appropriate amount of edge. I think I'd probably also use jumper cables to connect the shrouds to the mast at the base, creating a loop.

Looking at the rather low actual amount of metal below decks in my 26M, I don't see much that could produce what Casey calls "side flashes".

Another more permanent option might be to go ahead and install the 12' length of copper that Casey mentions, placing it so that the new through-hulls go into the ballast tank where a leak would be less critical. You'd still have to get a cable from that external plate to the mast somehow, though.

- AndyS

[Frank C]

I think the key thing to absorb from these articles is the fact that the charge dissipates from the edges of the grounding plate, ....
....... at the base of the mast to which you'd bolt, not clamp, a heavy conductive cable, the length of cable reaching the water, and bolted (welded?) to a piece of solid copper with the appropriate amount of edge...
....... Another more permanent option might be to go ahead and install the 12' length of copper that Casey mentions, placing it so that the new through-hulls go into the ballast tank where a leak would be less critical.

Andy,
As I wrote above, lightning is a very slight risk in most of California. We simply do not see many thunderstorms. However, it is always fun to muse about boating.

In freshwater the ground plate should have at least 24 feet of edge, typically accomplished by attaching a 12-foot length of inch-wide copper strap to the hull. Such a strap is six times as effective at dissipating a strike as a square plate with the same area.

I followed your logic until the last quote about thru-hulls into the ballast tank. I had imagined Casey's one-inch wide strip of copper wrapping around the centerboard, just inches aft from its leading edge. With board extended the ground-plate is deep in the water. With board retracted, the ground-plate is still at the waterline. The mast-to-ground connection could be strapped from compression post to the centerboard's hanger bracket, thence to the copper strip (ground-plate). If the connections were adequately radiused (a big 'if'), then the centerboard could serve as a sacrificial lamb.

One could also rim the lowest edge of the centerboard trunk with this 12-foot long copper strip, but I can just imagine that copper glowing cherry red and melting a hole right through the CB trunk. That would burn an awfully big hole in the bottom of the cabin!

[Andy26M]

Frank C -

Haha - the logic disconnect is because you are thinking of an X with the centerboard well, and I am thinking of an M.

On the M, the daggerboard slides down out of a hole which is maybe 2 feet long by 2 inches wide, and the daggerboard fits pretty snug inside, such that I would not immediately think of adding anything onto the board itself. The daggerboard trunk extends from the mast foot down to the "keel" directly, so there is no metal compression post there.

However, with a little glass work, you could probably put the copper strips right on/in the daggerboard, and then the grounding cable could ride up and down above the daggerboard just like the lift/drop lines do. You'd have to drop the daggerboard all the way during a storm, though, to get enough copper edge in the water. This is good thinking, Frank - now I have to go look at my daggerboard trunk a bit closer and see if there is a winter project in the offing!

As to the comment about though-hulls going into the ballast tank, it just seems to me that if I was drilling a hole in the boat, I'd prefer to drill it into the space that is full of water anyway. Of course this only works if you do not have to get to the back of the hole, i.e. it's for stuff that you're bolting on the outside of the hull. For instance, my depth sounder transducer is screwed in to an area that is definitely the ballast tank, then the cable runs externally up the transom and enters the boat via the engine cable grommet.

- AndyS

[Frank C]

Ahhhh soo .... (Andy 26M), guess it's not so mysterious if I'd just look!
Anyway, yeah, I think there may be merit to using the center foil on either boat. I wonder if you bought copper in flat stock, could you get something like 3/16" that you might adhere to each side of the board? The idea is to avoid fairing-in that flattened copper tube ... too much fiberglass work in that.

[Catigale]

Hope no one takes offense at this, but lightning is a complex and stochastic phenomena ..the "experts" cannot even agree on whether 'grounding' the mast decreases your chance of getting injured by lightning.


The best defense is not getting caught out - most (all?) of the persons on the this list are pleasure boaters and its our own d* fault for going out and getting caught when we shouldnt have. And before I sound too righteous, I got myself caught last May.

I have not grounded Catigale but have instead devoted my energy to recognising weather patterns and using the Radar tools before I go out.

[Frank C]

..the "experts" cannot even agree on whether 'grounding' the mast decreases your chance of getting injured by lightning.

Stephen,
No flames perceived nor intended, simply a counterpoint. I wrote the same above ... agree wholeheartedly! However, in many parts of the USA, if you avoid sailing on a day that you "might" see lightning, you simply won't sail (e.g. most of Florida). It's not unusual to find myself 60 minutes from shore, and from what I've read, a squall can overtake in half that time. If one chooses to cruise the Channel Islands off California, that means open water for half a day. Cruise to Bimini - make that open water exposure a full day.

California is particularly fortunate that lightning is rare, but since I like to trailer my boat, I'm still considering some form of lightning protection for those areas to which I travel. While I cannot vouch for the accuracy of Don Casey's article, I find the following two quotations very interesting:

A metal mast towering overhead would seem to heighten the danger (no pun intended), but as it turns out, that mast is actually your protector. It's powerboaters who most often get electrocuted by lightning. <comment: yes, he begs the question of the normal ratio, sail to power>

The idea of attracting lightning makes some sailors reluctant to ground the mast on their vessels. The logic behind this fear is fundamentally flawed for an aluminum mast .... because grounded or not, the mast is a better conductor than air. Ground the mast and a strike has a safe exit route. Leave out the ground and the strike will leap across the interior of the boat to some other metal component that is grounded, or it will simply blast through the hull to reach the water. There is no evidence that grounding the mast increases the likelihood of being struck, but compelling evidence that doing so reduces the risk of damage or injury if a strike does occur.<Emphasis added.>

Following your suggestions to a T won't completely eliminate the possibility of being caught in a boat by lightning. Casey's article might be wrong, but I think I'd draw some comfort from having followed his suggestions, even if most would call it voodoo.
P.S. I found your story about the airport delay - chilling - I bet you could have heard a pin drop!

[Duane Dunn, Allegro]

Three good articles, but in the end I think I'll just keep going out without a grounding system and hope that guy is correct. So far in 12 years we've only ended up out in two storms where there was lightning. No strikes so far.

I was glad to learn one thing though. One of the guys refered to walking around in a flat field and being the tallest thing around. Then when your hair stands on end your head becomes a source for the stream of positive charges up to meet the lightning. I'm glad to know that there is yet another advantage to being bald, with no hair on my head to stand up I'm safe from getting zapped.

[Catigale]

Thanks Frank

Its true in upstate NY our weather does tend to be more binary, where you can pretty much tell if lightning is likely or not. as a sidebar, I use a wireless internet connection to the wunderground.com website to access high resolution doppler radar from Catigale all over the US. Im usually inland so Im often 3 minutes from a beachable shore where I can watch the fireworks from a safe place...ill worry about the boat later.

My first and closest experience with lightning was as a youth on a soccer field - I saw a bolt come down and hit the goalpost, then travel vertically back up to a lightstand on the staidum some 1/4 mile away, then sideways to a building several hundred feet away.

This wasa vivid impression but makes me suspect adding a couple of feet of wire to "guide" the charge is hoohey.....but if it feels right to do it then I confess I would do it!!

I was with an experienced sailor when I was caught on the Hudson in May, and he taught me a clever trick - we circled a large buoy in the river during a squall(visibility < 75 feet) which

1. Kept us in a known location
2 Prevented us from becoming sailboat chum by freighter traffic (we stayed 5-10 feet from buoy)
3 I felt either way that the buoy was more likely to be hit than us so I felt safer. Im not saying I was safer, but I felt more comfortable..

Be safe out there!