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Lightning Protection questions
This winter's major project is to add some serious lightning protection to
"Strider". What I have now is probably sufficient to increase the odds of being alive to climb into the dinghy and watch the boat sink but I'd prefer to sail home. It's not a subject that comes up often for a designer of metal vessels so I've been look around the web and learned: The ABYS standards of 1 sq. foot of ground area and 8 GA conductors are marginal and highly suspect. Probably nothing feasible is going to protect a plastic boat in fresh water. Although I'm generally in salt, I'd like to be ready to go up some rivers. Conductors should have a minimum 8" radius bend. I've got a metal mast support strut that has sufficient through bolts to the mast deck step to make it electrically continuous. This lands on a wide, internal ballast keel. I plan to run flat copper straps about 1/16" x 1/2" (approximate cross section of 4 ga wire) from this up each side to 6" x 24" bronze ground plates on each side of the hull. These will be about 1/16" thick and through bolted to the hull at each corner. Inside, there will be straps under the bolt heads in an "X" pattern with the strap from the mast strut lead to the center. There will also be a 4 Ga wire or strap from the engine block to one of these plates to help protect the engine bearings. Comments welcome on this conceptual plan which will also include other secondary bonding additions as recommended by ABYC. Here's my main question for someone who understands high voltage better than I do: I only have 6" under the cabin sole. How critical is the 8" bend? Can I compensate for the tighter radius by increasing the conductor cross section? How much? The turn is more than 90 degrees because the straps have to run back up the hull deadrise about two feet to where I can locate the plates and through bolts. I don't think putting the plates on the keel sides is feasible. Another question: Is the standard metal rod VHF antenna at the top of the mast with the typical metal can on a bracket riveted to the mast a sufficient air terminal or should I add a dedicated rod? I have no illusions about having any electronics working after a strike on a 32 foot boat but replacement of my minimalist outfit wouldn't break me financially. I'd just like to be alive with a working engine and watertight boat. -- Roger Long |
Lightning Protection questions
On Sat, 8 Nov 2008 12:40:47 -0500, "Roger Long"
wrote: This winter's major project is to add some serious lightning protection to "Strider". What I have now is probably sufficient to increase the odds of being alive to climb into the dinghy and watch the boat sink but I'd prefer to sail home. It's not a subject that comes up often for a designer of metal vessels so I've been look around the web and learned: The ABYS standards of 1 sq. foot of ground area and 8 GA conductors are marginal and highly suspect. Probably nothing feasible is going to protect a plastic boat in fresh water. Although I'm generally in salt, I'd like to be ready to go up some rivers. Conductors should have a minimum 8" radius bend. I've got a metal mast support strut that has sufficient through bolts to the mast deck step to make it electrically continuous. This lands on a wide, internal ballast keel. I plan to run flat copper straps about 1/16" x 1/2" (approximate cross section of 4 ga wire) from this up each side to 6" x 24" bronze ground plates on each side of the hull. These will be about 1/16" thick and through bolted to the hull at each corner. Inside, there will be straps under the bolt heads in an "X" pattern with the strap from the mast strut lead to the center. There will also be a 4 Ga wire or strap from the engine block to one of these plates to help protect the engine bearings. Comments welcome on this conceptual plan which will also include other secondary bonding additions as recommended by ABYC. Here's my main question for someone who understands high voltage better than I do: I only have 6" under the cabin sole. How critical is the 8" bend? Can I compensate for the tighter radius by increasing the conductor cross section? How much? The turn is more than 90 degrees because the straps have to run back up the hull deadrise about two feet to where I can locate the plates and through bolts. I don't think putting the plates on the keel sides is feasible. Another question: Is the standard metal rod VHF antenna at the top of the mast with the typical metal can on a bracket riveted to the mast a sufficient air terminal or should I add a dedicated rod? I have no illusions about having any electronics working after a strike on a 32 foot boat but replacement of my minimalist outfit wouldn't break me financially. I'd just like to be alive with a working engine and watertight boat. I know of at least half a dozen sailboats that have been hit, one of them twice on the same day. Only one sank and that was because the lightning decided to exit through a plastic knot meter impeller leaving a 1 inch hole in the bottom. It could have been plugged if there had been anyone on board at the time. What you are planning sounds like overkill to me, especially for Maine. Where we live now there are thunderstorms almost everyday throughout the summer but you don't hear about that many hits on boats. Golfers seem to be the target of choice and they usually fare poorly. |
Lightning Protection questions
"Wayne.B" wrote
What you are planning sounds like overkill to me, especially for Maine. That's what I would have said (and did) earlier this year. However, I hear of more strikes as I get around more. One was my slip neighbor before I was docked there. I'm also thinking of some fresh water tripsafter my recent Hudson experience and would like to take the boat south for at least one winter. It's one of those things where a little more isn't incrementally a lot of work once you're set up to do the minimum. If I semi enjoy just one rip snorting boomber instead of quaking in the forward V-berth, it will be worth it. Besides, didn't we decide last year that "overkill" was my middle name? :) -- Roger Long |
Lightning Protection questions
Roger,
Talk to these people: http://www.lightningtech.com/intro.html They are the authority on this subject. Joe |
Lightning Protection questions
Roger Long wrote:
This winter's major project is to add some serious lightning protection to "Strider". What I have now is probably sufficient to increase the odds of being alive to climb into the dinghy and watch the boat sink but I'd prefer to sail home. It's not a subject that comes up often for a designer of metal vessels so I've been look around the web and learned: Do it like is done for tall buildings, strap a copper ribbon, 8" x 1/4" up the length of your mast, one on each side. bond these at the base of the mast to copper bus, 8" x 1/2", this bus is then bonded to a braided copper cable approximately 6" in diameter and led to copper grid. The grid should consist of an array of 1/2" diameter rod laid out to form a square of no less 100' on each side, or any configuration giving you an area of 10,000 sq. ft. The rods should be configured to form squares of about one foot on each side, each junction should be bonded. The main cable should be laid across at least 3/4 of the grid, or the braid unraveled and broken into many smaller strands, each strand to be bonded to the grid at intervals of two to five feet. This will probably, but is not guaranteed to, protect your boat, remember a lighting strike may exceed a million amperes, for a brief time, but it does have a tendency of vaporizing anything smaller than I have described. Cheers Martin |
Lightning Protection questions
"Roger Long" wrote in message ... This winter's major project is to add some serious lightning protection to "Strider". What I have now is probably sufficient to increase the odds of being alive to climb into the dinghy and watch the boat sink but I'd prefer to sail home. It's not a subject that comes up often for a designer of metal vessels so I've been look around the web and learned: The ABYS standards of 1 sq. foot of ground area and 8 GA conductors are marginal and highly suspect. Probably nothing feasible is going to protect a plastic boat in fresh water. Although I'm generally in salt, I'd like to be ready to go up some rivers. Conductors should have a minimum 8" radius bend. I've got a metal mast support strut that has sufficient through bolts to the mast deck step to make it electrically continuous. This lands on a wide, internal ballast keel. I plan to run flat copper straps about 1/16" x 1/2" (approximate cross section of 4 ga wire) from this up each side to 6" x 24" bronze ground plates on each side of the hull. These will be about 1/16" thick and through bolted to the hull at each corner. Inside, there will be straps under the bolt heads in an "X" pattern with the strap from the mast strut lead to the center. There will also be a 4 Ga wire or strap from the engine block to one of these plates to help protect the engine bearings. Comments welcome on this conceptual plan which will also include other secondary bonding additions as recommended by ABYC. Here's my main question for someone who understands high voltage better than I do: I only have 6" under the cabin sole. How critical is the 8" bend? Can I compensate for the tighter radius by increasing the conductor cross section? How much? The turn is more than 90 degrees because the straps have to run back up the hull deadrise about two feet to where I can locate the plates and through bolts. I don't think putting the plates on the keel sides is feasible. Another question: Is the standard metal rod VHF antenna at the top of the mast with the typical metal can on a bracket riveted to the mast a sufficient air terminal or should I add a dedicated rod? I have no illusions about having any electronics working after a strike on a 32 foot boat but replacement of my minimalist outfit wouldn't break me financially. I'd just like to be alive with a working engine and watertight boat. To understand lightning you've got to understand why it strikes. You need to "see" the world how lightning sees the world. You get an unbalanced electrical charge between the clouds and the water. Like all current, lightning takes the path of least resistance. This may or may not have anything to do with height of mast. Height of mast and material of mast and grounding of mast all have little to do with how lightning "sees" the best path to ground. The purpose of all the bonding and grounding is to bleed off charge slowly before it builds up to a great enough extent to arc from above the boat. A properly grounded GRP sailboat will be seen by lightning potential directly over it as sitting in a valley. One not grounded at all will be seen as sitting atop a hill. Again, it's not distance I'm talking about but resistance in the path to ground. An ungrounded boat does not bleed off potential. It spikes it up. The trouble with grounding your boat properly is the slow bleeding off of the charge imbalance can actually, in some cases, prepare a lower resistance path to ground as charge is already moving that way. While it may thwart lightning strikes from directly above, should lightning strike at a 45 degree angle, for example, it may well strike a well-grounded boat and not strike an ungrounded boat anchored several boat lengths away. But, a properly grounded boat will suffer less damage as the voltage will not build up as much because the current (amperage) will flow easier to ground. An ungrounded boat, though less likely to be "seen" by lightning will, if struck, suffer more damage because the voltage will build higher and the resultant amperage will also be higher. My boat is totally ungrounded and in over 25 years has been struck only once. I was aboard and all kinds of bad stuff happened. There was a zzzzzzt and a huge crash simultaneously. Then a series of gun shots as ball lightning went arching and dancing around everywhere inside. I was forward lying in the v-berth. One ear on the pillow and the other up. It was temporarily deafened for a couple days in the upper ear and had extensive ringing but the hearing came back. I think I was knocked unconscious for a couple of minutes. My hair smelled burnt. Every wired electronic device but one GPS was cooked. Solar panels were fried from the inside out. The wiring harness was cooked. All the lights burned out. A charred hole the size of a walnut was blasted out of the GRP ceiling where the cabin light wires were encapsulated. The backstay where it split was burned in two on the port side where current arched from it to the outboard motor the foot of which was in the water acting as a ground. The current jumped from the backstay to the tiller handle and cooked the wiring and throttle cable - burned them to a crisp. The plastic fuel tank had black marks on it but wasn't burned through. The ignition was not ruined, however, probably because most of it is under the metal flywheel. The base-loaded VHF antenna at the mast head was an empty shell. The mast wiring inside was all cooked. The depth sounder transponder was fried. Bottom paint was blasted off the outside of two of the bronze thru hulls. The keel bolts above the GRP floors were blackened. The boat was full of smoke. A bottle of brandy in the undersink galley locker had burst and was burning in the bilge. The Adler Barbour fried. The secretary at a nearby marina saw the strike. She said is was very large and lasted seconds hitting again and again. It cost over 4,000 dollars not counting my labor time to repair it all. However the good news is the cast iron keel took the brunt of it with paint and epoxy coating blasted off in several fist-sized places. The hull at the water line took no damage. No leaks as a result. No hull damage. There was some deck damage at the foot of the mast were the current actually passed through to get to the wood enclosed steel post that supports the deck stepped mast foot and then to the keel bolts. The choices as I see them are these: a) Bond and ground your boat well and be prepared to be hit more often but with less damage. b) Don't bond and ground and your boat will be struck less often but with more damage. b) has been and will continue to be my choice as proper grounding and bonding can only really be done during the construction process. Once a boat is built too much stuff has to be torn out to do the job right. Wilbur Hubbard |
Lightning Protection questions
On Sat, 8 Nov 2008 12:40:47 -0500, "Roger Long"
wrote: This winter's major project is to add some serious lightning protection to "Strider". What I have now is probably sufficient to increase the odds of being alive to climb into the dinghy and watch the boat sink but I'd prefer to sail home. It's not a subject that comes up often for a designer of metal vessels so I've been look around the web and learned: The ABYS standards of 1 sq. foot of ground area and 8 GA conductors are marginal and highly suspect. Probably nothing feasible is going to protect a plastic boat in fresh water. Although I'm generally in salt, I'd like to be ready to go up some rivers. Conductors should have a minimum 8" radius bend. I've got a metal mast support strut that has sufficient through bolts to the mast deck step to make it electrically continuous. This lands on a wide, internal ballast keel. I plan to run flat copper straps about 1/16" x 1/2" (approximate cross section of 4 ga wire) from this up each side to 6" x 24" bronze ground plates on each side of the hull. These will be about 1/16" thick and through bolted to the hull at each corner. Inside, there will be straps under the bolt heads in an "X" pattern with the strap from the mast strut lead to the center. There will also be a 4 Ga wire or strap from the engine block to one of these plates to help protect the engine bearings. Comments welcome on this conceptual plan which will also include other secondary bonding additions as recommended by ABYC. Here's my main question for someone who understands high voltage better than I do: I only have 6" under the cabin sole. How critical is the 8" bend? Can I compensate for the tighter radius by increasing the conductor cross section? How much? The turn is more than 90 degrees because the straps have to run back up the hull deadrise about two feet to where I can locate the plates and through bolts. I don't think putting the plates on the keel sides is feasible. Another question: Is the standard metal rod VHF antenna at the top of the mast with the typical metal can on a bracket riveted to the mast a sufficient air terminal or should I add a dedicated rod? I have no illusions about having any electronics working after a strike on a 32 foot boat but replacement of my minimalist outfit wouldn't break me financially. I'd just like to be alive with a working engine and watertight boat. Wear a tin-foil hat if it stops you worrying.. http://www.google.co.uk/search?sourc...ng+cosmic+rays |
Lightning Protection questions
On Sat, 8 Nov 2008 12:40:47 -0500, "Roger Long"
wrote: I'd just like to be alive with a working engine and watertight boat. The wise Craptain Neal filled his boat with empty bottles and inflatable dolls so that it was unsinkable.(like the Titanic) |
Lightning Protection questions
On Sat, 08 Nov 2008 16:33:21 -0500, Marty wrote:
Roger Long wrote: This winter's major project is to add some serious lightning protection to "Strider". What I have now is probably sufficient to increase the odds of being alive to climb into the dinghy and watch the boat sink but I'd prefer to sail home. It's not a subject that comes up often for a designer of metal vessels so I've been look around the web and learned: Do it like is done for tall buildings, strap a copper ribbon, 8" x 1/4" up the length of your mast, one on each side. bond these at the base of the mast to copper bus, 8" x 1/2", this bus is then bonded to a braided copper cable approximately 6" in diameter and led to copper grid. The grid should consist of an array of 1/2" diameter rod laid out to form a square of no less 100' on each side, or any configuration giving you an area of 10,000 sq. ft. The rods should be configured to form squares of about one foot on each side, each junction should be bonded. The main cable should be laid across at least 3/4 of the grid, or the braid unraveled and broken into many smaller strands, each strand to be bonded to the grid at intervals of two to five feet. This will probably, but is not guaranteed to, protect your boat, remember a lighting strike may exceed a million amperes, for a brief time, but it does have a tendency of vaporizing anything smaller than I have described. Sounds like BS. My house barn and corn crib all had half inch or so braided copper cable connecting 1/2 inch pointed rods. The ground rods are presumed to be the standard ones the electrical places all sell. They were struck hundreds of times, they were on top of a hill. I heard it was 20 000 amps, at a million volts. Casady |
Lightning Protection questions
Richard Casady wrote:
Sounds like BS. My house barn and corn crib all had half inch or so braided copper cable connecting 1/2 inch pointed rods. The ground rods are presumed to be the standard ones the electrical places all sell. They were struck hundreds of times, they were on top of a hill. I heard it was 20 000 amps, at a million volts. Guess I should have included a tongue and a cheek,,, However my point was rather that lightening is inherently unpredictable. Our barn is "protected" the same as yours, still has the cool glass globes at the base of the pointed rods, what the hell they are supposed to do I don't know. As far as I know it's never been hit. I've seen a neighbor's lightening system vaporized, fortunately it was raining hard enough, and his roof was leaky enough that damage was limited to a some singed hay and a couple of scorched boards. I've been involved with ground protection systems for airports, (counterpoises in the trade) and seen some absolutely whacky things, like edge lighting halogen bulbs blown up, even though the feeder was buried three feet below a 4 gauge bare copper ground wire just a few inches below ground..... I've seen constant current power supplies that feed the lighting fried but the lighting fixtures and transformers remain unharmed.... lighting is funny stuff.. Cheers Martin |
Lightning Protection questions
On Sat, 08 Nov 2008 23:35:13 -0500, Marty wrote:
Richard Casady wrote: Sounds like BS. My house barn and corn crib all had half inch or so braided copper cable connecting 1/2 inch pointed rods. The ground rods are presumed to be the standard ones the electrical places all sell. They were struck hundreds of times, they were on top of a hill. I heard it was 20 000 amps, at a million volts. Guess I should have included a tongue and a cheek,,, However my point was rather that lightening is inherently unpredictable. Our barn is "protected" the same as yours, still has the cool glass globes at the base of the pointed rods, what the hell they are supposed to do I don't know. As far as I know it's never been hit. I've seen a neighbor's lightening system vaporized, fortunately it was raining hard enough, and his roof was leaky enough that damage was limited to a some singed hay and a couple of scorched boards. I've been involved with ground protection systems for airports, (counterpoises in the trade) and seen some absolutely whacky things, like edge lighting halogen bulbs blown up, even though the feeder was buried three feet below a 4 gauge bare copper ground wire just a few inches below ground..... I've seen constant current power supplies that feed the lighting fried but the lighting fixtures and transformers remain unharmed.... lighting is funny stuff.. Pretty much my take based on fairly extensive reading. Think I came to the conclusion that: Bonding can pretty much provide a safe area so long as you keep you hands off metal. An electrical disconnect that won't likely be jumped might be worth exploring to cut down the expense of damaged electronics. Basically like pulling the plugs in the house, which I usually do during electrical storms. Keep some portable radio/gps gear in an insulated container. Since you might get holed, have a good collection of damage control plugs. Dry weather lightning can still catch you off-guard. --Vic |
Lightning Protection questions
"Roger Long" wrote in
: s the standard metal rod VHF antenna at the top of the mast with the typical metal can on a bracket riveted to the mast a sufficient air terminal or should I add a dedicated rod? I have no illusions about having any electronics working after a strike on a 32 foot boat but replacement of my minimalist outfit wouldn't break me financially. I'd just like to be alive with a working engine and watertight boat. -- Roger Long http://www.thomson.ece.ufl.edu/lightning/ This sailor has done extensive research at ufl..... |
Lightning Protection questions
On Sat, 8 Nov 2008 14:48:10 -0500, "Roger Long"
wrote: I'm also thinking of some fresh water tripsafter my recent Hudson experience and would like to take the boat south for at least one winter. There are almost no thunderstorms in south Florida from November through May. We call it the dry season here for good reason. |
Lightning Protection questions
Larry wrote:
http://www.thomson.ece.ufl.edu/lightning/ This sailor has done extensive research at ufl..... Thanks, that was one of the first things I turned up. This quote is especially applicable to this thread in view of Wilbur's comment that an ungrounded boat is less likely to be struck: "While the individual estimates varied widely between surveyors, there is no support for the argument presented by some sailors that they should not ground 'their sailboat since it will increase the chances of it being struck by lightning." The statistics presented in this article make a good case for just forgetting about it unless I plan to sail south, which I do hope to do at some point. My original post was actually prompted by this and a couple of other web articles. Here is my situation: http://home.maine.rr.com/rlma/Keel.jpg The mast stanchion is essentially equal to a keel stepped mast. Since my boat was originally a keel / centerboarder, the keel is large volume and I doubt that Endeavour spent the money for a keel casting. I'm quite sure the ballast is just stacked lead pigs in resin. Lighting current going through that stuff would be like a bomb and the high resistance at the bottom of the main conductor would create extensive side flashing. For reasons not evident on the crude drawing, any grounding plates have to be outboard of the cabin sole. The Thomson paper says not to let grounding conductors contact the hull but I have no choice if I am to maintain the maximum radius recommended by other sources. The reason for overkill on conductor and ground plate size is to compensate for the tight conductor radius and need to run the conductors close to the hull skin. -- Roger Long -- Roger Long |
Lightning Protection questions
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Lightning Protection questions
wrote in message ... Protecting a sailboat from lightning strikes is pretty much a fools errand. Unless you have witnessed lightning strikes up close and personal, you have no idea of the forces involved. It beats any "fantasy explosions" or other special effects mayhem you have ever seen in the movies. A 1/2 inch copper wire would vaporize before it could carry the strike anywhere. You aren't going to steer a lightning bolt, either. It has no brains and will often jump a long distance, even if already following what seems to be a path. The best thing you can do for lightning protection on a sailboat is anchor near other boats with taller masts than yours, and THAT is also foolishness and completely useless. It's only benefit is a little humor. Some years ago I was caught in a lightning storm while well offshore. My boat had a metal mast with a pointy VHF aerial on top. The mast was keel stepped, but the step seemed to be just glassed into the hull and I could see no sign that it was bonded to the lead keel. Lightning bolts were hitting the water so close to us that I could distinctly hear the sizzling noise of water boiling and this happened several times. Despite the fact that my mast was the only thing sticking up above sea level in the vicinity we were not struck although it was a very frightening experience. I am afraid that this does not assist in deciding whether earthing the mast is a good idea or not.. |
Lightning Protection questions
Roger Long wrote:
Larry wrote: http://www.thomson.ece.ufl.edu/lightning/ This sailor has done extensive research at ufl..... Thanks, that was one of the first things I turned up. This quote is especially applicable to this thread in view of Wilbur's comment that an ungrounded boat is less likely to be struck: "While the individual estimates varied widely between surveyors, there is no support for the argument presented by some sailors that they should not ground 'their sailboat since it will increase the chances of it being struck by lightning." The statistics presented in this article make a good case for just forgetting about it unless I plan to sail south, which I do hope to do at some point. My original post was actually prompted by this and a couple of other web articles. Here is my situation: http://home.maine.rr.com/rlma/Keel.jpg The mast stanchion is essentially equal to a keel stepped mast. Since my boat was originally a keel / centerboarder, the keel is large volume and I doubt that Endeavour spent the money for a keel casting. I'm quite sure the ballast is just stacked lead pigs in resin. Lighting current going through that stuff would be like a bomb and the high resistance at the bottom of the main conductor would create extensive side flashing. For reasons not evident on the crude drawing, any grounding plates have to be outboard of the cabin sole. The Thomson paper says not to let grounding conductors contact the hull but I have no choice if I am to maintain the maximum radius recommended by other sources. The reason for overkill on conductor and ground plate size is to compensate for the tight conductor radius and need to run the conductors close to the hull skin. -- Roger Long The problem is, lightning doesn't like going round corners and *will* jump back out of the lightning conductor at the bend. E.M. Thompson states: At this time the peak lightning current is generated, during the 'return stroke'. Although cresting at ten thousand to hundreds of thousands of amps, it only lasts for about a millionth of a second. This 1 us pulse considered in the frequancy domain has a fundamental at 1 MHz and various unspecified (we dont really know the pulse shape) strong harmonics going *way* up. As a mimimum, the grounding system *MUST* have a low impedance from DC to 10 MHz which essentially prohibits anything except large radius bends through less than 90 degrees. Due to the 10 KA current pulse, an extremely high voltage will be developed accross any bend, so there is an extreme risk of arcing to the hull if the bent strap is in the bilge. If its touching the hull, you basically needn't have bothered fitting it from the point it touches the hull onwards to the grounding plate. The other nice little problem is that multiple KA currents *will* straighten out any sharp bends in the conductor carrying them and a lightning strike consists of multiple strokes so the grounding system has to survive in usable condition to be effective. The main lightning conductors need to be joined to the mast support post at least as high above the grounding plates as the lateral distance and led in a smoothly swept curve. Unless your pillar is very close to a bulkhead this may not be practically achivable. Once you've led the lightning below decks, you are basically screwed unless you can lead it almost streight down and out. Once you've led it below the waterline you are totally ****ed unless you can get it out to large area grounding plates. From your description, I dont see how anything except boring the top of the keel downwards and outwards for thick pure copper conducters to ground plates extending from the sides of the keel to the turn of the bilge could help much. There are problems with this approach as well, as the conducters will try to move quite a bit duing the strike and if undersised and they go open circuit during the strike could cause major explosive damage to your keel root. |
Lightning Protection questions
wrote:
Protecting a sailboat from lightning strikes is pretty much a fools errand. This document, which Larry provided the link to, contriticts you with actual facts by researchers. http://www.thomson.ece.ufl.edu/lightning/ See damage distribution graphs. There will usually be some damage and some strikes will overwhelm any system. However, saying protection is pointless is like saying it's a fools errand to wear seatbelts because some car crashes will be fatal anyway. Everything on the water is about odds. Stack the deck in your favor when you can. -- Roger Long |
Lightning Protection questions
Sounds like I'd better stay north of Cape Cod:)
I've thought of drilling the keel since lead is fairly easy to drill. I'd want to be sure there wasn't any scrap iron in the ballast mix though. How thick a copper conductor do you think would be safe? The mast support is only about 1 1/2" stainless steel pipe so it would be reasonable to exceed it's cross section area and current carrying capacity. OTOH if the mast support itself is insufficient, maybe I should just forget the whole thing and put my faith in prayer. I ran a copper wire of the kind used to ground electrical meters from one of the shroud chainplates to an unused through hull in a fairly gentle sweep when I first got the boat just to have something to lead a strike a way from people inside. I still expect a major strike would sink the boat but thought it might increase the chances of being alive to get into the dinghy. Now I'm thinking I might be better off without this connection. What do you think? What would be the probable effectiveness of a portable system? Say, four 1 sq foot copper plates attached to 4 GA wires shackled to headstay, backstay, and shrouds before anchoring or drifting for a major electrical storm? -- Roger Long |
Lightning Protection questions
On Nov 9, 8:24*am, "Roger Long" wrote:
Sounds like I'd better stay north of Cape Cod:) I've thought of drilling the keel since lead is fairly easy to drill. *I'd want to be sure there wasn't any scrap iron in the ballast mix though. How thick a copper conductor do you think would be safe? *The mast support is only about 1 1/2" stainless steel pipe so it would be reasonable to exceed it's cross section area and current carrying capacity. *OTOH if the mast support itself is insufficient, maybe I should just forget the whole thing and put my faith in prayer. I ran a copper wire of the kind used to ground electrical meters from one of the shroud chainplates to an unused through hull in a fairly gentle sweep when I first got the boat just to have something to lead a strike a way from people inside. *I still expect a major strike would sink the boat but thought it might increase the chances of being alive to get into the dinghy. Now I'm thinking I might be better off without this connection. *What do you think? What would be the probable effectiveness of a portable system? *Say, four 1 sq foot copper plates attached to 4 GA wires shackled to headstay, backstay, and shrouds before anchoring or drifting for a major electrical storm? -- Roger Long 4 gauge may be a bit small. A fellow in my old marina took a scrap welders lead and cut 6 ft sections and had them saddled clamped to the shrouds on each side, had them coiled and zip tied to each side. In a storm he just cut them loose and figured that would be the least path of resistance right down into the water. As Neal's example proved when the lighting jumped in an air arch to his skull lightning seeks the path of least resistance. I dont think he's been struck yet to test his system. He has many taller boats all around him. Joe |
Lightning Protection questions
On Sun, 9 Nov 2008 08:48:03 -0500, "Roger Long"
wrote: wrote: Protecting a sailboat from lightning strikes is pretty much a fools errand. This document, which Larry provided the link to, contriticts you with actual facts by researchers. http://www.thomson.ece.ufl.edu/lightning/ See damage distribution graphs. There will usually be some damage and some strikes will overwhelm any system. However, saying protection is pointless is like saying it's a fools errand to wear seatbelts because some car crashes will be fatal anyway. Everything on the water is about odds. Stack the deck in your favor when you can. You seem hell-bent on installing a protection system, and I understand the feeling. "Because I can." "Reach for the stars." "Dream the impossible dream." (-: Go for it. Whenever the discussion comes up, I'm hoping for new data. The Thomson stuff is old, and I don't see where he had convincing data to come to a conclusion. I wish the boat insurance industry would do some work on their data. Are there insurance premium discounts for lightning protection systems on boats? I found the Sea Grant pamphlet link provided on the above the most useful piece on lightning and boats that I've seen. The algebra-laced IEEE paper sorely tests my attention span, but Larry probably eats it up. --Vic |
Lightning Protection questions
How about this?
http://home.maine.rr.com/rlma/Ground.jpg I hauled out 180 feet of chain and removed my bilge storm chain locker for a better look and measurements. This is close to scale. The ground is shown in red. This would be about two square feet of 1/16" copper glued to the hull and screwed in way of the ballast fill. A 1/2" diameter silicon bronze bolt would go through the copper and hull. This is the same cross section area as the stainless steel mast stanchion. The connection between the mast stanchion and the through bolt would be a 1/8" copper bracket with bent flanges for resistance to the mechanical forces of the charge. This would be machine screwed to the pipe stanchion from the back. A refinement would be to make the through bolt longer and fasten it to the side of the bracket with through bolts for a more straight line electrical path. -- Roger Long |
Lightning Protection questions
Just a thought, has anyone looked at a faraday cage? http://www.juliantrubin.com/bigten/f...periments.html |
Lightning Protection questions
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Lightning Protection questions
On Sat, 08 Nov 2008 22:49:50 -0600, Vic Smith
wrote: Keep some portable radio/gps gear in an insulated container. What you want is a completely closed metal container. The charge will stay in the walls of the container. They call this a Faraday Cage. Casady |
Lightning Protection questions
Roger Long wrote:
How about this? http://home.maine.rr.com/rlma/Ground.jpg I hauled out 180 feet of chain and removed my bilge storm chain locker for a better look and measurements. This is close to scale. The ground is shown in red. This would be about two square feet of 1/16" copper glued to the hull and screwed in way of the ballast fill. A 1/2" diameter silicon bronze bolt would go through the copper and hull. This is the same cross section area as the stainless steel mast stanchion. The connection between the mast stanchion and the through bolt would be a 1/8" copper bracket with bent flanges for resistance to the mechanical forces of the charge. This would be machine screwed to the pipe stanchion from the back. A refinement would be to make the through bolt longer and fasten it to the side of the bracket with through bolts for a more straight line electrical path. Doesn't look too bad, definately better than leaving it alone. As I mentioned previously, this is much like a HF grounding problem (except a DC path is required and the expected current level. That would lead me to suspect that multiple bolts between the copper bracket and the grounding plate would be in order. Take full width copper plates bolted on fore and aft of the support strut out to ground plates port and starboard. If you can persuade the current to split fairly evenly you gain *much* more protection from explosive events round those 1/2" through hull bolts as resistive heating will be proportional to I^2. If you manage to split the current evenly between four bolts, two each side, the energy dissipated in each bolt will be reduced by a factor of 16. I wouldnt bother with the longer bolts bent and bolted to the bracket, You'd be better off with triangular pieces brazed accross the corner of the bracket to its flange either side of each bolt, leaving just enough room to get the end of a spanner in. If everything is nicely faired in and you round off all sharp edges to the largest radius possible you should have minimal structural and underwater damage. There is likely to be at least *some* moisture behind the exterior grounding plates so I would expect a steam explosion especially at their edges. Screwing them into the ballast keel is probably not a good idea. Drill and countersink holes in the plates *ONLY* to provide a key and epoxy them into place? They will probably come loose at the edges in a strike but hopefully will remain connected at the through bolts. If you can keep the encapsulated ballast from being involved, you've basically won. Have you considerd that the odds are that you *WONT* have a startable engine unless you can either hand start it or have a spare starting battery kept fully isolated and a spare starter motor. Also you will probably have damage to control cables and possibly to any metal fuel lines depending on their proximity to other items. I've seen photos of lightning damage to a mast with multiple holes you could stick several fingers through down it for about a quarter of its length so rig failure is also a real possibility. |
Lightning Protection questions
On Sun, 9 Nov 2008 08:48:03 -0500, "Roger Long"
wrote: wrote: Protecting a sailboat from lightning strikes is pretty much a fools errand. This document, which Larry provided the link to, contriticts you with actual facts by researchers. http://www.thomson.ece.ufl.edu/lightning/ See damage distribution graphs. There will usually be some damage and some strikes will overwhelm any system. However, saying protection is pointless is like saying it's a fools errand to wear seatbelts because some car crashes will be fatal anyway. Everything on the water is about odds. Stack the deck in your favor when you can. Do you wear a nomex suit and crash helmet when driving a car. Does your car have a fire suppression system? Those would be a LOT more important to your safety than anything you can do to protect a sailboat from lightning. By the time you equipped your boat with what would be needed to protect you in SOME lightning hits, it would no longer be useable as a sailboat. Those huge copper fields you would have to drag around would really slow you down... Getting hit in the head by the boom is a much greater threat, anyway, if you want to go by statistics. Simply falling overboard has a very high mortality rate. Lightning protection on a sailboat is a fools errand. |
Lightning Protection questions
Thanks, this is very helpful. I'd planned on the flanges being arranged so
that the nut of the through bolt is sort of in the end of a box. By extending the flange against the hull and making the top and bottom edge flanges triangular, I could get in two or more bolts. My problem is that this all has to be done from one side so I can't put bolts forward of the mast strut or main vertical plate. If I keep extending the bolt flange along the hull back to add additional bolts, do I run into a situation of diminishing returns? It would be nice to simply duplicate the arrangement on the other side but I have wires and plumbing running through that side of the bilge. I know I'll still have a lot of damage in event of a major strike but I'd like to be figuring out my next move sitting aboard the boat than swimming or sitting in a dinghy waiting for the next bolt. Most boats that I have heard of being struck in this part of the world had only electronics damage. even without good protection, so something like this should heavily weight the odds in my favor. Is there any advantage or downside to making this conductor out of multiple laminations of 1/16" copper sheet? -- Roger Long |
Lightning Protection questions
I don't know why my first Google search missed this site:
http://www.marinelightning.com/ but it calls into question the whole idea of the central main conductor. I'm fortunate in having one of those aluminum toe rails that go bow to stern on each side. It seems that I might be better off running the heaviest wire I can between the port and starboard toe rails inside at bow and stern and then bonding each chainplate to the toe rail and running 4 ga conductors to each piece of underwater metal I can. I have a number of unused through hulls that are capped. The chainplates on my boat all end very close to the toe rail so charge coming down the stays would likely jump that way even without bonding. -- Roger Long |
Lightning Protection questions
Roger Long wrote:
I don't know why my first Google search missed this site: http://www.marinelightning.com/ but it calls into question the whole idea of the central main conductor. I'm fortunate in having one of those aluminum toe rails that go bow to stern on each side. It seems that I might be better off running the heaviest wire I can between the port and starboard toe rails inside at bow and stern and then bonding each chainplate to the toe rail and running 4 ga conductors to each piece of underwater metal I can. I have a number of unused through hulls that are capped. The chainplates on my boat all end very close to the toe rail so charge coming down the stays would likely jump that way even without bonding. As I said earlier, If you let the lighting get below deck, you are screwed and if down to bilge level ****ed unless its got somewhere to go. For a powerboat or a sailboat with a non-conductive mast support post, its probably practical to *NOT* have a central lightning conductor, but where do you think the bulk of the lightning current is going to go? Down a nice thick piece of low resistance aluminium bolted inline to a heavy fairly low resistance steel pipe leading to the bilge or down fairly high resistance shrouds and stays with rather dodgy electrical contact at the top and bottom ends? There is going to be *some* current down the stays so it would appear prudent to bond the toerail to the shrouds, stays and mast foot, and cross bond bow and stern, but then the problem is where do you encourage the inevitable flashover from the toerail to the water surface to go? A strap down the stem and each transom corner would be a good start but few owners are going to tolerate external straps down from the chainplates. I suppose you could trail a chain from each shroud while berthed and if caught out in a thunderstorm. |
Lightning Protection questions
"IanM" wrote in message
... Roger Long wrote: I don't know why my first Google search missed this site: http://www.marinelightning.com/ but it calls into question the whole idea of the central main conductor. I'm fortunate in having one of those aluminum toe rails that go bow to stern on each side. It seems that I might be better off running the heaviest wire I can between the port and starboard toe rails inside at bow and stern and then bonding each chainplate to the toe rail and running 4 ga conductors to each piece of underwater metal I can. I have a number of unused through hulls that are capped. The chainplates on my boat all end very close to the toe rail so charge coming down the stays would likely jump that way even without bonding. As I said earlier, If you let the lighting get below deck, you are screwed and if down to bilge level ****ed unless its got somewhere to go. For a powerboat or a sailboat with a non-conductive mast support post, its probably practical to *NOT* have a central lightning conductor, but where do you think the bulk of the lightning current is going to go? Down a nice thick piece of low resistance aluminium bolted inline to a heavy fairly low resistance steel pipe leading to the bilge or down fairly high resistance shrouds and stays with rather dodgy electrical contact at the top and bottom ends? There is going to be *some* current down the stays so it would appear prudent to bond the toerail to the shrouds, stays and mast foot, and cross bond bow and stern, but then the problem is where do you encourage the inevitable flashover from the toerail to the water surface to go? A strap down the stem and each transom corner would be a good start but few owners are going to tolerate external straps down from the chainplates. I suppose you could trail a chain from each shroud while berthed and if caught out in a thunderstorm. From my manual: 22:00 LIGHTENING PROTECTION AND BONDING SYSTEMS All Sabre yachts are equipped with a heavy duty lightening ground and bonding system connecting all essential equipment to the keel using #8 gauge stranded copper wire. 22:01 BONDING SYSTEM: The bonding system provides low resistance to electrical connections of all underwater fittings, fuel fill, fuel tank and engine to the keel. This keeps all fittings at the same electrical potential to minimize the effects of any galvanic or electrical corrosion which may occur. Any additional underwater hardware installed on the boat must be tied in to the bonding system to maintain proper operation and protection from corrosion. The integrity and operation of the system should be checked each year at launching and hauling times. Refer to the lightening protection and bonding system diagrams in the back of the Owners Manual for the wiring details of your boat. 22:02 LIGHTENING PROTECTION SYSTEM: The lightening protection system provides a "cone" of protection around the boat in the even of a lightening storm. Grounding wires of #8 gauge copper connect all chain plates and the mast step to the keel. The integrity of the lightening ground system should be checked regularly. Inspect all wire and terminal connections at the mast step, all chainplates and the keep for tightness and signs of corrosion. Lightening strikes are unpredictable, so due caution during a storm is advised. Allow no one in the water during an electrical storm. Remain inside the boat and avoid making contact with any large metal objects such as the mast, shrouds, stanchions, bow pulpit, stern rail or any of the items connects to the lightening grounding system, especially in such a way as to bridge between any of these items. If a boat is struck by lightening, there is likely to be damage to delicate electronic instruments due to a high voltage-low ampere surge of electricity through the boat. If a boat is struck by lightening, compasses and electrical gear must be checked for damage and/or change in calibration. Refer to the lightening protection and bonding system diagrams in the back of the Owners Manual for the wiring details of your boat. 23:03 BONDING AND LIGHTENING GROUND SYSTEM: Check the entire bonding and lightening ground systems to assure that they are intact and functioning properly. The purpose of the bonding systems is to protect the underwater hardware from corrosion by providing a low resistance path to ground for any stray electrical currents which may develop on the boat. All underwater hardware is tied together with a wiring system which terminates at one or two common ground terminals on a keel bolt in the bilge. The integrity and operation of the bonding system can be checked by using an ohmmeter to assure that each underwater fitting is bonded to the keel. The ohmmeter must register "0" resistance for each fitting. The "Lightening Protection and Bonding System" diagram will help in locating all fittings and hardware connected to the bonding system. If little or no contact is found between a fitting and the keel, connections at each end of the wire must be checked and the wire replaced if necessary. Particular attention should be paid to the engine to keel bonding conductor. Our experience indicates that a poor ground connection here can often allow a stray current to leave the boat by way of the propeller shaft. -- "j" ganz @@ www.sailnow.com |
Lightning Protection questions
Last month one of the boats on the hard at the local yacht club got hit - hard. It looked like the bolt hit near the _bottom_ of the mast. (and yes, the mast was up) So were the masts of thirty other boats around it. All on trailers, too. But this one was the one. Insurance had lapsed the month before. The resulting fire was so hot that the boat beside this one melted. I'm guessing that if you took a hit like this, you'd never know it. -- Richard (remove the X to email) |
Lightning Protection questions
Capt. JG wrote:
"IanM" wrote in message ... Roger Long wrote: I don't know why my first Google search missed this site: http://www.marinelightning.com/ but it calls into question the whole idea of the central main conductor. I'm fortunate in having one of those aluminum toe rails that go bow to stern on each side. It seems that I might be better off running the heaviest wire I can between the port and starboard toe rails inside at bow and stern and then bonding each chainplate to the toe rail and running 4 ga conductors to each piece of underwater metal I can. I have a number of unused through hulls that are capped. The chainplates on my boat all end very close to the toe rail so charge coming down the stays would likely jump that way even without bonding. As I said earlier, If you let the lighting get below deck, you are screwed and if down to bilge level ****ed unless its got somewhere to go. For a powerboat or a sailboat with a non-conductive mast support post, its probably practical to *NOT* have a central lightning conductor, but where do you think the bulk of the lightning current is going to go? Down a nice thick piece of low resistance aluminium bolted inline to a heavy fairly low resistance steel pipe leading to the bilge or down fairly high resistance shrouds and stays with rather dodgy electrical contact at the top and bottom ends? There is going to be *some* current down the stays so it would appear prudent to bond the toerail to the shrouds, stays and mast foot, and cross bond bow and stern, but then the problem is where do you encourage the inevitable flashover from the toerail to the water surface to go? A strap down the stem and each transom corner would be a good start but few owners are going to tolerate external straps down from the chainplates. I suppose you could trail a chain from each shroud while berthed and if caught out in a thunderstorm. From my manual: 22:00 LIGHTENING PROTECTION AND BONDING SYSTEMS All Sabre yachts are equipped with a heavy duty lightening ground and bonding system connecting all essential equipment to the keel using #8 gauge stranded copper wire. 22:01 BONDING SYSTEM: The bonding system provides low resistance to electrical connections of all underwater fittings, fuel fill, fuel tank and engine to the keel. This keeps all fittings at the same electrical potential to minimize the effects of any galvanic or electrical corrosion which may occur. Any additional underwater hardware installed on the boat must be tied in to the bonding system to maintain proper operation and protection from corrosion. The integrity and operation of the system should be checked each year at launching and hauling times. Refer to the lightening protection and bonding system diagrams in the back of the Owners Manual for the wiring details of your boat. 22:02 LIGHTENING PROTECTION SYSTEM: The lightening protection system provides a "cone" of protection around the boat in the even of a lightening storm. Grounding wires of #8 gauge copper connect all chain plates and the mast step to the keel. #8? Ha, Jon, I've seen the inside of an underground vault with the walls spattered with copper after a 75KA short vaporized copper bus bars 1/2'" thick by 4" wide. That's one hell of lot of #8 wires in parallel. Imagine what happens with surge that may exceed 200KA? I go along with others that have suggested that lightning protection for a plastic boat is probably an exercise in futility. Cheers Martin |
Lightning Protection questions
Roger Long wrote:
Thanks, this is very helpful. I'd planned on the flanges being arranged so that the nut of the through bolt is sort of in the end of a box. By extending the flange against the hull and making the top and bottom edge flanges triangular, I could get in two or more bolts. OK, Keep the box section but widen it vertically against the hull to allow for two bolts. Add a rib down to the flange between the bolts. After a trial fit has been done and all fixing bolts tightened to conform it to the hull, take it out and braze or silver solder any joints. My problem is that this all has to be done from one side so I can't put bolts forward of the mast strut or main vertical plate. Difficult. I presume there is a bulkhead in the way. Can you get a strap round the front of the mast bolted to the copper bracket either side sufficiently far out that it doesn't have sharp bends in it? It wont have as good contact to the support post but should help prevent flashover at the angle from the post to the bracket for relatively little cost and difficulty of installation. If I keep extending the bolt flange along the hull back to add additional bolts, do I run into a situation of diminishing returns? Yes. Two bolts a side is practical, three would be possible, more would be of little benefit. Also the bolts should be as close as possible to the main body of the flange and the same distance from it or the closest will hog the current and the others be less effective. It would be nice to simply duplicate the arrangement on the other side but I have wires and plumbing running through that side of the bilge. There is no reason why the other copper bracket cant have some big holes in it for plumbing and other services, Just bolt braze or rivet a strap of cross sectional area equivalent to the thickness times hole diameter to both the top and bottom edges of the bracket. I know I'll still have a lot of damage in event of a major strike but I'd like to be figuring out my next move sitting aboard the boat than swimming or sitting in a dinghy waiting for the next bolt. Most boats that I have heard of being struck in this part of the world had only electronics damage. even without good protection, so something like this should heavily weight the odds in my favor. Is there any advantage or downside to making this conductor out of multiple laminations of 1/16" copper sheet? Corrosion and getting even current sharing between the layers are against you. Better to go thicker rather than thinner. Dont loose sight of the fact that you *KNOW* you dont want any current flowing down through the blocks of ballast in the keel and exploding the possibly somewhat damp resin between them and blowing chunks of the skin off. It also seems advisable to review your chain stowage. If its too close to the foot of the support post, you will get side flashes out through the hull via the chain. I've looked over http://www.marinelightning.com/ and they dont seem to say anything aboout the problem of a keel stepped mast (or a metal mast support post) and the monohull installation link leads to a single roughly annotated photo - not encouraging. Some good ideas and info though especially for those of us with deck stepped masts without a metal support post. |
Lightning Protection questions
Marty wrote:
Capt. JG wrote: 22:02 LIGHTENING PROTECTION SYSTEM: The lightening protection system provides a "cone" of protection around the boat in the even of a lightening storm. Grounding wires of #8 gauge copper connect all chain plates and the mast step to the keel. #8? Ha, Jon, I've seen the inside of an underground vault with the walls spattered with copper after a 75KA short vaporized copper bus bars 1/2'" thick by 4" wide. That's one hell of lot of #8 wires in parallel. Imagine what happens with surge that may exceed 200KA? I go along with others that have suggested that lightning protection for a plastic boat is probably an exercise in futility. Cheers Martin #8 is obsolete. #4 grounding wires are now called for. Also I'd lay odds that the 75KA short lasted for several cycles of your 60Hz mains before the breakers cleared it. It almost certainly had more than 1000 times the energy that a 100KA 1us lightning strike would dissipate in a single #8 cable. If the protection system can prevent serious structural damage from 9 strikes out of 10 its obviously worth doing. If it reduces damage 50% of the time so you dont have to abandon ship in the middle of a storm its still worth doing if the cost is comparable to that of a liferaft. |
Lightning Protection questions
"Roger Long" wrote in
: The mast stanchion is essentially equal to a keel stepped mast. Since my boat was originally a keel / centerboarder, the keel is large volume and I doubt that Endeavour spent the money for a keel casting. I'm quite sure the ballast is just stacked lead pigs in resin. Lighting current going through that stuff would be like a bomb and the high resistance at the bottom of the main conductor would create extensive side flashing. For reasons not evident on the crude drawing, any grounding plates have to be outboard of the cabin sole. The Thomson paper says not to let grounding conductors contact the hull but I have no choice if I am to maintain the maximum radius recommended by other sources. The reason for overkill on conductor and ground plate size is to compensate for the tight conductor radius and need to run the conductors close to the hull skin. -- Roger Long I've been involved in tower grounding (just a mast 1200' high with no sails, if we can help it) for decades in broadcasting. The AM towers are series fed, meaning they are insulated from ground but have two trailer hitch balls a few inches apart (far enough so the 5, 10, 25 or 50KW transmitters don't make them arc in the downpouring rainstorms.) Looking around Jim Hawkins' broadcast transmitter website, you can learn a lot about lightning grounding from the professionals: http://www.hawkins.pair.com/radio.html Let's look at the feedpoint of WFAN/WCBS AM stations whos twin 50,000 watt transmitters across the river from NYC share one tower. (The RF comes out of the building on that copper tubing with the rain loop in it.) The 900', i think, tower sits on a large brown ceramic insulator. The ring around the outside of the insulator has a lightning gap to that metal ball hooked to the ground plate on top of the concrete base. radiating out from the base are large copper ground straps that hook to another ring, to distribute the hundreds of thousand of amps of current from the stroke, and there is a ring of ground rods driven to bed rock with a pile driver around that ring, the ring attached to the top of them. The key to these grounding systems is their SHORT, STRAIGHT AS POSSIBLE, LOW IMPEDANCE path. Lightning is not considered DC in these designs. It is a PULSE of power with an amazing bandwidth in frequencies. The length of the conductors increases INDUCTANCE, which raises the impedance to the very quick pulse. Impedance is our enemy. As it rises, so does the voltage drop across it, raising the voltage on the upper end of it. Any sharp corners MUST be avoided as that makes a little 1 turn COIL raising impedance to the pulse. Ground strap must CURVE around a large radius, as discussed in the article, to reduce impedance and pulse voltage drop. By the way, most big AM stations use the Harris DX-50 solid state 50KW transmitters now. They use 55KW of power from the power company to put out 50KW of RF to the antenna...This is one of the 230 switching modules that actually provide the RF power: http://www.hawkins.pair.com/wabcnow/wabcn14.jpg All the cooling it needs is a few big muffin fans through those little heat sinks to put out a blowtorch of AM radio power! Amazing technology. If you wanna see more, look he http://www.hawkins.pair.com/wcbs_wfan.html Most people have no idea where the signal comes from. They think it comes from the studio where the stupid talking heads live. http://www.hawkins.pair.com/wado/wadotowrleg.jpg Here's a similar base at WADO, formerly WNEW. It has two lightning balls across the massive insulator. The odd looking intertwined rings are called Austin transformers. The RF won't flow between the rings because they are far apart and provide fairly good isolation. What DOES go across between these coils is 60 cycle AC power, magnetically coupled, that light the tower lights you see day and night for those folks riding to their deaths in airliners. See all the direct, large ground straps heliarc welded to the ground system under the tower? Low impedance...low voltage....only a few hundred volts of pulse in a stroke to this huge tower. http://www.hawkins.pair.com/wor/wor_tower08.jpg This picture of the base of WOR's towers shows "Johnny Bells" and the lightning balls to ground. Lightning flows out to the edge of the bells then jumps the gap to the balls. ================================================== ================= Your only hope is to BYPASS the lightning's current AROUND the passengers and hull so it doesn't HAVE to jump THRU it, punching holes in the expensive plastique. There are many "paths" to get the lightning off the mast. The base of the mast must be connected to the sea as short and direct as possible. From the above pictures, you can see how big the conductor SHOULD be, but that's not very practical in most boats. Keel stepped masts are easy. Copper straps to the inside of the hull clamped between large stainless washers and 2 nuts where the grounding block mounting bolts come through the hull. Coat it all in your favorite sealant, but make sure you leave it where the sealant can be shed so the grounding blocks can be replaced as they eventually will be eaten. I guess it's too ugly to expect painted straps down the OUTSIDE of the hull to the same bolts UNDER the grounding blocks from the lower end of the shrouds, another great path from mast to sea around the people, hull and expensive electronics. Backstay and Forestay ends also need grounding blocks underwater to bleed off the charge around the ends of it. Just dreaming....I've been knocked flat being between the backstay and steering wheel in the way of lightning arcing between them. You'll never forget it......so close. |
Lightning Protection questions
"Roger Long" wrote in news:gf6rq3$mk0$1
@registered.motzarella.org: Sounds like I'd better stay north of Cape Cod:) I doubt 1 in 100 boats in Charleston Harbor have any ground systems at all. They all survive the summer storms just fine. We do NOT have those blinding thunderstorms of the Northeast US or western Florida, though. Ours are caused by localized thunderstorms that rise up in huge thermals over the swamps just inland and the wind blows them over us. |
Lightning Protection questions
Wayne.B wrote in
: On Sat, 8 Nov 2008 14:48:10 -0500, "Roger Long" wrote: I'm also thinking of some fresh water tripsafter my recent Hudson experience and would like to take the boat south for at least one winter. There are almost no thunderstorms in south Florida from November through May. We call it the dry season here for good reason. Yeah, but Florida makes up for it in spades between June and September....bigtime! |
Lightning Protection questions
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