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Voyager
Master Marine Consultant

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USA
5397 Posts

Initially Posted - 02/23/2008 : 16:40:16

I was just re-reading my Power Squadron Marine Electronics course book, as well as a book by Don Casey entitled Sailboat Electrics Simplified about lightning protection.

I searched back in the forums and found several strings discussing this topic and realized that while all the text books pretty much clearly state what must be done to create the "Safety Cone" around small sailboats, nothing is ever so cut and dried, especially considering the behavior of lightning.

While my basic instinct is to stay out of danger in the first place, of course last summer my wife and I found ourselves taken completely by surprise (and so was the Weather Service) when a small but powerful thunderstorm blew through our area at 45kts. We did not get struck, but quite a few bolts hit nearby. We hove to and rode it out.

I'm a betting man (usually) when it comes to forces that are so very unpredictable, and I prefer to stack the odds and go with the recommendations of the experts.

Reading through all the materials I believe I must ground the mast and at least the port and starboard chainplates to the keel using #4 solid wire (I have a fixed keel boat).

Since the electrical system is not grounded centrally except to the control panel, I do not plan to use a zinc on the keel to prevent galvanic currents (but that's a whole different topic!)

I've seen folks who clamp a long thick jumper cable to each of the stay turnbuckles and drop the other end in the water attached to big chunk of steel. This approach, although its not pretty, works very well, especially in salt water. I prepared for this approach on my daysailor, but never needed it.

Fresh water is another story. The recommendation is to use a long, thin electrode in the water. But with the keel, I figure I'm fine, either in the saltwater of LI Sound, or in the brackish or fresh water up in the river.

What's the current thinking on this topic among the members?

Bruce Ross
Passage ~ SR-FK ~ C25 #5032

Port Captain � Milford, CT

Edited by - on

John Russell
Master Marine Consultant

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USA
3444 Posts

Response Posted - 02/23/2008 : 16:53:31

Given your profession, I'm not sure too many will want to disagree with you but, there is something to be said for the idea of improving the route to ground actually will attract more strikes than it will prevent. I have ZERO expertise or experience here, but I stopped reading when I read that somewhere. Just makes sense to me.

Edited by - on

Steve Milby
Past Commodore

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USA
5904 Posts

Response Posted - 02/23/2008 : 17:05:25

One of our members wrote a treatise of moderate length on the subject and posted it on his website. I haven't read it for a long time, but remember it being exceptionally thoughtful and well written. You can find it by clicking on the following hyperlink:

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

Edited by - Steve Milby on 02/23/2008 17:06:28

Chris Z
Captain

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452 Posts

Response Posted - 02/23/2008 : 18:55:18

Okay, I thought after seeing so much discussion I would see what the Mythbusters have to say.
http://community.discovery.com/eve/forums/a/tpc/f/9701967776/m/8281971559?r=8281971559#8281971559

Edited by - on

redviking
Master Marine Consultant

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USA
1771 Posts

Response Posted - 02/24/2008 : 09:51:12

Bruce, you have the right idea. Grounding the mast will be hard and I suggest you go for the heavy chain method you described. Grounding the mast also has the unfortunate byproduct of possibly blowing a hole out the bottom when struck - or so I have heard. C25 keel bolts could blow out? Dunno! We were near a lightning storm recently and even though the VHF was off - there was power to it, but it was off - it turned itself on and stayed on 16, refused all imput and was OK the next morning. We awoke to it beeping and chirping, but couldn't do anything with it. Couldn't change channels, turn it off, nothing.... Hit master power and went back to sleep after storing all GPS units and related electronic items in the OVEN... Lightning fries electronics, so a steel box helps - supposedly...

Sten

DPO C25 #3220 "Zephyr", SR, FK
SV Lysistrata - C&C 39 - St. Augustine FL, heading south to the islands in a week or two NOW after the canvas guy finishes! @##$%%^&&**()))!!!!

Edited by - on

Voyager
Master Marine Consultant

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USA
5397 Posts

Response Posted - 02/24/2008 : 18:09:04

As I read more about this, it seems that little is actually known based upon cold hard facts - actual experience. The truth seems to be, grounded or not, getting your sailboat hit by lightning is a relatively rare experience, and that's probably why so little is known about it.

One thing that is very well documented, however, it that near-misses and direct-hits both take a toll on your electronics. Sten - you were lucky that your VHF and GPS didn't go completely kaput!

The Stewart paper seems very well reasoned and gives you a lot to think about. It also appears they are continuously collecting anecdotal evidence from readers over time. From the looks of things about 25 people responded, about 1/2 being hit by lightning and for the rest, lightning hit nearby.

Of those whose masts were hit, most had grounded masts and a whip antenna attached. This supports the theory that you're encouraging lightning to hit you if your mast is grounded. The good news is that arc-over or side bolts of lightning is minimized if your grounding is solid.

A surprising finding is presented: whether the captain grounds the mast intentionally or not, the author considers any boat with an inboard engine or through hull transducer to be grounded by default: the anchor light or VHF cable is connected to the boat's electrical control panel, and ground cables connect to the engine/prop or transducer from there.

Seems like we're just starting to peel back this onion.

Seeing this is the case, I plan to install a #4 cable from the mast step to the keel bolts this season.

Edited by - on

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 02/25/2008 : 09:21:51

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Voyager
 ...I plan to install a #4 cable from the mast step to the keel bolts this season.<hr height="1" noshade id="quote"></blockquote id="quote">Be aware that the keel itself is apparently insulated with a good inch or more of "stuff"--I can't say exactly what it is, but it's sorta like asbestos furnace insulation covered by gelcoat. I suspect it's that way so the shape with the denser lead ballast is the same as the less dense cast iron (which had no cover).

Otherwise, if you've read the older threads on this, you know my opinion, which I do not propose that anybody adopt. I do suspect that doing it wrong can easily be worse than not doing anything. On the other hand, there's very little agreement on what "right" is.

Edited by - on

Voyager
Master Marine Consultant

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USA
5397 Posts

Response Posted - 02/25/2008 : 21:16:13

Dave -
Since the connection is already there (anchor light - switch panel - depth sounder - transducer ) I reckon I'm just making the connection better between the mast head and the water.

The trick is to embed a 2 sqft copper plate into/onto the bottom of the boat. Since I plan to remove the thru-hull for the depth sounder, I may be able to add the plate right there and connect it using a #4 wire down from the mast.

Edited by - on

dmpilc
Master Marine Consultant

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USA
4593 Posts

Response Posted - 02/25/2008 : 22:57:41

There's a guy here who had an Oday 27 that was hit by lightning (that's what he gets for always having to have the tallest mast, which it was at the time). In addition to frying his electronics, when he hauled out, it looked like someone had blasted his keel with several rounds from a shotgun. His keel was peppered by the exiting electrical current from the lightning bolt.

Edited by - on

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