I have done considerable research into lightning protection for sailboats and haven't found any definitive guidelines. Some sources say ground the mast, others say don't attract lightning with a rod. There is an excellent video online from a fellow in Florida who illustrates the risks of not grounding the mast, and I agree with his view. I am currently refurbishing a 1972 Bristol 34 (Gusto), and am bonding all my major metal, but my sea cocks are plastic and no longer work as a ground point (as they did in bronze when the boat was originally built). I may install a ground plate during the next haulout, but have read about explosion problems with that method. Meanwhile, I have rigged a flexible 1/0 cable from the mast near the cabin top at the partners. The cable stays coiled in a bag on deck most of the time. The theory is that I can toss the wire overboard in lightning conditions to provide a very low resistance path to ground. My wire rig is similar in concept to the Strikeshield device sold from Canada (they are on the net). Mine is of course home made, with an aluminum electrode on the end of the cable, and the wire is permanently attached tot he mast. But I think it will work as well as the Strikeshield.
I'd like some comments on this "toss over" design, and on lightning protection in general. I feel very naked when sailing in lightning, and I hope my new rig will ease my mind a bit. But, am I fooling myself? Any comments on lightning protection?
Lightning protection
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George ( Triton #236 )
Hi Artzat,
I've done a chunk of research on lightning protection too and you can read what I've written in the MIR section of the National Triton Association website under "Lightning Protection".
You are correct in many of your decisions though. First, grounding the mast and attaching a lightning rod has no real world effect on your chances of being hit by lightning ( so do it ). Second, a big fat ground cable straight down to ground is the best way to go.
Most of the scientific literature I've read ( and by scientific I mean someone with an actual PHD in engineering or physics wrote it ) indicates that you need a minimum if one sq. ft. of metal as a discharge point which is why copper ground plates are often used - especially in fresh water. If I remember correctly, the Strikeshield company's setup you mentioned uses ground plates on both sides of the boat. I'm not sure I've seen an instance of a well connected ground plate exploding ( but would love to add it to my records ), please send a url of the article if you have it handy. My e-mail is gjones1735@cox.net. Also, there is a Yahoogroups listserve for people interested in "Lightning Protection" It's mostly people in the business and some research scientists. Good stuff.
I think that a large electrode over the side and under 6' of water and connected to the mast with 1/0 cable can work well. The only problem is that it can't be used while underway ( at least not without grinding up the side of your boat ).
Good luck with the project,
George
Triton hull #236
I've done a chunk of research on lightning protection too and you can read what I've written in the MIR section of the National Triton Association website under "Lightning Protection".
You are correct in many of your decisions though. First, grounding the mast and attaching a lightning rod has no real world effect on your chances of being hit by lightning ( so do it ). Second, a big fat ground cable straight down to ground is the best way to go.
Most of the scientific literature I've read ( and by scientific I mean someone with an actual PHD in engineering or physics wrote it ) indicates that you need a minimum if one sq. ft. of metal as a discharge point which is why copper ground plates are often used - especially in fresh water. If I remember correctly, the Strikeshield company's setup you mentioned uses ground plates on both sides of the boat. I'm not sure I've seen an instance of a well connected ground plate exploding ( but would love to add it to my records ), please send a url of the article if you have it handy. My e-mail is gjones1735@cox.net. Also, there is a Yahoogroups listserve for people interested in "Lightning Protection" It's mostly people in the business and some research scientists. Good stuff.
I think that a large electrode over the side and under 6' of water and connected to the mast with 1/0 cable can work well. The only problem is that it can't be used while underway ( at least not without grinding up the side of your boat ).
Good luck with the project,
George
Triton hull #236
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artzat
Lightning protection web sites
Thanks for the leads on lignthing sites.
For anyone interested, the Ewen Thomson lightning video can be viswed online at http://www.thomson.ece.ufl.edu/lightning/video.html.
The strikeshiled site is strikeshield.com I think it has info on problems with exploding ground plates made from porus copper (i.e. radio grounds).
I modeled my single wire ground wire after the cheapest version of Strikeshield. I tried it for the first time just the other day, and was surprised at how well it travelled in the water. We were sailing in calm water at 4-6 knots, and it drifted along nicely far below the surface. I don't think it ever hit the boat, but if it did it was a slient hit. I don't figure on using it often, so some mild some minor scratching on the bottom if it keeps me from frying.
Arthur Z.
For anyone interested, the Ewen Thomson lightning video can be viswed online at http://www.thomson.ece.ufl.edu/lightning/video.html.
The strikeshiled site is strikeshield.com I think it has info on problems with exploding ground plates made from porus copper (i.e. radio grounds).
I modeled my single wire ground wire after the cheapest version of Strikeshield. I tried it for the first time just the other day, and was surprised at how well it travelled in the water. We were sailing in calm water at 4-6 knots, and it drifted along nicely far below the surface. I don't think it ever hit the boat, but if it did it was a slient hit. I don't figure on using it often, so some mild some minor scratching on the bottom if it keeps me from frying.
Arthur Z.
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George ( Triton #236 )
Hi Arthur,
I know what you are talking about now. The exploding raido ground plate you mentioned is not a copper plate at all but a matrix of bronze spheres known as "Sintered Bronze". Made famous under the trade name "Dynaplate" by the Guest corporation. A good solid copper ground plate is what you want at the discharge point. Also, remember a good bi-metallic connector at the mast to help keep corrosion down.
I'm still not sold on heavy electrodes hanging free over the side of the boat while sailing. They can work well at anchor but I've just spent the last two weeks sailing through thunderstorms and squall lines on the Chesapeake and the descriptions "calm" or "4-6 knots" were not to be found. I really think that a heavy cable connected from the base of the mast straight down to a two foot square copper discharge plate at the turn of the keel is the best way to go. However, I do like the idea of the lightning never entering the main cabin.
We didn't get hit once on the trip although lightning struck close by on several occassions. I really do think that it's tougher to get hit than most people imagine. Good luck with the project.
George
I know what you are talking about now. The exploding raido ground plate you mentioned is not a copper plate at all but a matrix of bronze spheres known as "Sintered Bronze". Made famous under the trade name "Dynaplate" by the Guest corporation. A good solid copper ground plate is what you want at the discharge point. Also, remember a good bi-metallic connector at the mast to help keep corrosion down.
I'm still not sold on heavy electrodes hanging free over the side of the boat while sailing. They can work well at anchor but I've just spent the last two weeks sailing through thunderstorms and squall lines on the Chesapeake and the descriptions "calm" or "4-6 knots" were not to be found. I really think that a heavy cable connected from the base of the mast straight down to a two foot square copper discharge plate at the turn of the keel is the best way to go. However, I do like the idea of the lightning never entering the main cabin.
We didn't get hit once on the trip although lightning struck close by on several occassions. I really do think that it's tougher to get hit than most people imagine. Good luck with the project.
George