*5 By Gosh I take my hat off to Arlyn of Texas. that was the most intellectual post I have ever read. To the point and full of knowlage. Hip Hip Horay Arlyn.
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old barn lightning rods
Tom... yes, what you describe is exactly what is found on some old barns and houses. A lightning rod that has a glass bulb dielectric. Such a rod stays above ground so as not to attract...but if one does hit, the small air dielectric of the bulb will transfer the strike past the bulb to ground. Unfortunately as our tech world spins... we forgot that there were many understandings that are timeless. Put a small air dielectric in the ground wire near the keel, then the best of both sides of the issue are handled... the boat stays above ground not to attract, and if it does take a hit... there is a system to handle it.
Tom... yes, what you describe is exactly what is found on some old barns and houses. A lightning rod that has a glass bulb dielectric. Such a rod stays above ground so as not to attract...but if one does hit, the small air dielectric of the bulb will transfer the strike past the bulb to ground. Unfortunately as our tech world spins... we forgot that there were many understandings that are timeless. Put a small air dielectric in the ground wire near the keel, then the best of both sides of the issue are handled... the boat stays above ground not to attract, and if it does take a hit... there is a system to handle it.
Is the 'ground' passive?
The impression I got from the older threads and from my EE friend was that there was some sort of charge that initially proceeds from the surface or recipient area that the lightning then 'meets', which then appears to be a simple one-directional bolt. The 'groundwire' that we have used is a small wire not intended to channel major electricity but rather to guarantee that there is no difference in electrical potential between the masthead and the sea, so that the boat is a 'neutral' target. In a minor charge, it would also help save onboard electronics. If you are right, then perhaps the mast should be grounded for a moment to dissipate any hidden potential on board, and then ungrounded or 'neargrounded' when close to danger like you suggest?
The impression I got from the older threads and from my EE friend was that there was some sort of charge that initially proceeds from the surface or recipient area that the lightning then 'meets', which then appears to be a simple one-directional bolt. The 'groundwire' that we have used is a small wire not intended to channel major electricity but rather to guarantee that there is no difference in electrical potential between the masthead and the sea, so that the boat is a 'neutral' target. In a minor charge, it would also help save onboard electronics. If you are right, then perhaps the mast should be grounded for a moment to dissipate any hidden potential on board, and then ungrounded or 'neargrounded' when close to danger like you suggest?
Capacitance & Lightning
Capacitors & Lightning: Arlyn’s dielectric analysis of how lightning attaches to a boat, while (perhaps) emotionally appealing, neglects several important issues, and represents a gross over-simplification of a very complex phenomena. While I'm not prepared (nor perhaps competant) to get into a complete scientific debate of his contentions, I think it important to respectfully challenge this posting. For further consideration: The potential difference between a thunder cloud and ground (in our case the water), which results in a lightning strike, may vary between 100 Thousand and Many Millions of volts. A lightning strike will have traveled up to 10's of miles, across wet ionized air, prior to attaching itself to ground (through your mast or otherwise). A lightning strike is not merely a “DC” (Direct Current) event. Because of the very rapid (about 1 millionth of a second) build-up of current, from zero to as much as 300 Thousand Amperes, lightning is also an “EMP” (Electro-Magnetic Pulse), or “RF” (Radio Frequency) event. A typical (if such a thing exists) lightning strike is not a single episode; but consists of a sequence of several events . There are the: - connection (attachment) of the stepped leader from cloud to ground streamer - return stroke (huge amperage, very short duration) - continuing currents (smaller current, longer duration) - subsequent leader - return strokes & etc. While Arlyn is entitled to his opinion, and to draw his own conclusions, I think it important to point out that his logic is not in keeping with the overwhelming body of scientific thought on the subject, which may be summarized as: - Lightning is capricious and unpredictable. - It is impossible to effectively isolate (insulate) a boat from ground (water). - Bonding does NOT appear to increase the likelihood of being struck by lightning. - Bonding IS likely to decrease the damage caused if lightning strikes. In short, I’ve found no scientific evidence to support the contention that “grounding a boat shortens the path to ground”, and a great preponderance of counter-opinion. A very short bibliography: http://www.thomson.ece.ufl.edu/lightning/SGEB17.html http://www.cdc.gov/nasd/docs/d000001-d000100/d000007/d000007.pdf http://www.thomson.ece.ufl.edu/lightning/IEEE.pdf OMO Respectfully, Gord
Capacitors & Lightning: Arlyn’s dielectric analysis of how lightning attaches to a boat, while (perhaps) emotionally appealing, neglects several important issues, and represents a gross over-simplification of a very complex phenomena. While I'm not prepared (nor perhaps competant) to get into a complete scientific debate of his contentions, I think it important to respectfully challenge this posting. For further consideration: The potential difference between a thunder cloud and ground (in our case the water), which results in a lightning strike, may vary between 100 Thousand and Many Millions of volts. A lightning strike will have traveled up to 10's of miles, across wet ionized air, prior to attaching itself to ground (through your mast or otherwise). A lightning strike is not merely a “DC” (Direct Current) event. Because of the very rapid (about 1 millionth of a second) build-up of current, from zero to as much as 300 Thousand Amperes, lightning is also an “EMP” (Electro-Magnetic Pulse), or “RF” (Radio Frequency) event. A typical (if such a thing exists) lightning strike is not a single episode; but consists of a sequence of several events . There are the: - connection (attachment) of the stepped leader from cloud to ground streamer - return stroke (huge amperage, very short duration) - continuing currents (smaller current, longer duration) - subsequent leader - return strokes & etc. While Arlyn is entitled to his opinion, and to draw his own conclusions, I think it important to point out that his logic is not in keeping with the overwhelming body of scientific thought on the subject, which may be summarized as: - Lightning is capricious and unpredictable. - It is impossible to effectively isolate (insulate) a boat from ground (water). - Bonding does NOT appear to increase the likelihood of being struck by lightning. - Bonding IS likely to decrease the damage caused if lightning strikes. In short, I’ve found no scientific evidence to support the contention that “grounding a boat shortens the path to ground”, and a great preponderance of counter-opinion. A very short bibliography: http://www.thomson.ece.ufl.edu/lightning/SGEB17.html http://www.cdc.gov/nasd/docs/d000001-d000100/d000007/d000007.pdf http://www.thomson.ece.ufl.edu/lightning/IEEE.pdf OMO Respectfully, Gord
Yes...it is a simplification ...
I agree that it is a simplication of all the dynamics involved with lightning... and its not my desire to portray lightning as a simple concept. Here is a pic... demonstrating what I'm trying to say... http://www.stewartfam.net/arlyn/relative_grounds.JPG I do have a problem with some of the current acceptable thought... Don Casey for example describes that the logic that an ungrounded boat resist a hit is flawed because the mast is a better conductor than moist air. Thats true, but his logic is indeed flawed... because he is not viewing the dielectric value of the boat in its totality... in others words taking the hull in consideration as well as the mast.
I agree that it is a simplication of all the dynamics involved with lightning... and its not my desire to portray lightning as a simple concept. Here is a pic... demonstrating what I'm trying to say... http://www.stewartfam.net/arlyn/relative_grounds.JPG I do have a problem with some of the current acceptable thought... Don Casey for example describes that the logic that an ungrounded boat resist a hit is flawed because the mast is a better conductor than moist air. Thats true, but his logic is indeed flawed... because he is not viewing the dielectric value of the boat in its totality... in others words taking the hull in consideration as well as the mast.
Dielectric
Arlyn: Your analysis assumes two dielectric values; humid air @ 0.3 and hull @ 2.6, both of which are arbitrary, and likely inaccurate. You ignore the effects of ionization, which reduces the air’s dielectric strength to (more or less) Zero. You further ignore the effects of surface moisture on the hull, which could be expected to reduce it’s dielectric (which you’ve extrapolated from polystyrene). For the sake of argument, lets say that we could accurately determine the (more or less) exact dielectric strength of the air, mast, & hull. I don’t think that the relatively small dielectric differences that might be calculated (between a bonded and an un-bonded mast), would be in any way significant, to a lightning bolt that would have had to jump an air gap of many miles (in order to attach). You are trying to inject VERY SMALL values (which are, themselves, “suspect”) into an equation comprised of HUGE values, and derive significant conclusions from the potential (pun intended) differences. Remember, an equation can be no more accurate than it’s least accurate value; and the smallest factor will have the smallest effect. While I applaud your attempt to make a rational analysis of the likely effects of bonding or not (it’s an important safety subject), and cannot fault your suspicion of conventional wisdom [when people start agreeing with me, I re-examine my position
], I think you are reading way too much significance into your dielectric hypothesis. Your claim that “...it worked for me once” (staying ungrounded) is also unsubstantiated. The fact that lightning struck the water (nearby) could attributed to all sorts of un-named causes (perhaps the red shirt you were wearing, or your wife’s prayer). You cannot attribute cause & effect without some supporting evidence - it’s not logical. Respectfully, Gord
Arlyn: Your analysis assumes two dielectric values; humid air @ 0.3 and hull @ 2.6, both of which are arbitrary, and likely inaccurate. You ignore the effects of ionization, which reduces the air’s dielectric strength to (more or less) Zero. You further ignore the effects of surface moisture on the hull, which could be expected to reduce it’s dielectric (which you’ve extrapolated from polystyrene). For the sake of argument, lets say that we could accurately determine the (more or less) exact dielectric strength of the air, mast, & hull. I don’t think that the relatively small dielectric differences that might be calculated (between a bonded and an un-bonded mast), would be in any way significant, to a lightning bolt that would have had to jump an air gap of many miles (in order to attach). You are trying to inject VERY SMALL values (which are, themselves, “suspect”) into an equation comprised of HUGE values, and derive significant conclusions from the potential (pun intended) differences. Remember, an equation can be no more accurate than it’s least accurate value; and the smallest factor will have the smallest effect. While I applaud your attempt to make a rational analysis of the likely effects of bonding or not (it’s an important safety subject), and cannot fault your suspicion of conventional wisdom [when people start agreeing with me, I re-examine my position
], I think you are reading way too much significance into your dielectric hypothesis. Your claim that “...it worked for me once” (staying ungrounded) is also unsubstantiated. The fact that lightning struck the water (nearby) could attributed to all sorts of un-named causes (perhaps the red shirt you were wearing, or your wife’s prayer). You cannot attribute cause & effect without some supporting evidence - it’s not logical. Respectfully, GordI go with the theory that I had a Red Sox
cap on. Its been 85 years since they won a world series. Come on, whats the chance of lightning striking twice? ;-) There might be a few near misses along the way, but I think I'm safe. Only one thing that would be safer and that's if I had a Chicago Cubs cap on. Oops....don't look now we might get hiy by lightning !!
cap on. Its been 85 years since they won a world series. Come on, whats the chance of lightning striking twice? ;-) There might be a few near misses along the way, but I think I'm safe. Only one thing that would be safer and that's if I had a Chicago Cubs cap on. Oops....don't look now we might get hiy by lightning !!
picture
You ignore the effects of ionization, which reduces the air’s dielectric strength to (more or less) Zero. Did I? Did you miss the ion leader in the picture which is labeled - Dynamic ground height dependent on length of ion leader. Doesn't that suppose that the ion trail is near zero dielectric? A discussion needs listening to each other... adios
You ignore the effects of ionization, which reduces the air’s dielectric strength to (more or less) Zero. Did I? Did you miss the ion leader in the picture which is labeled - Dynamic ground height dependent on length of ion leader. Doesn't that suppose that the ion trail is near zero dielectric? A discussion needs listening to each other... adios
Ionization
ARLYN: You're absolutely right, I did miss the "Ionized Leader" (I believe it's actually the "Streamer", the "Leader" normally descends from the cloud) - as you say, I wasn't listening [knowing what you were going to say]. My apologies. As I said, the physics of this thing are way beyond my competence (or the interest of the board) - so (once again) I'll refer to "higher authority". I've found no learned literature (applied nor academic) supporting your theory. You've, obviously given the matter considerable thought, & I wonder if you've found any outside support for your thesis? If so, I'd deeply appreciate a reference. Respectfully, Gord
ARLYN: You're absolutely right, I did miss the "Ionized Leader" (I believe it's actually the "Streamer", the "Leader" normally descends from the cloud) - as you say, I wasn't listening [knowing what you were going to say
]. My apologies. As I said, the physics of this thing are way beyond my competence (or the interest of the board) - so (once again) I'll refer to "higher authority". I've found no learned literature (applied nor academic) supporting your theory. You've, obviously given the matter considerable thought, & I wonder if you've found any outside support for your thesis? If so, I'd deeply appreciate a reference. Respectfully, GordUnground Mast Hit
A few years ago. A Hunter 42 which was out of the water at the yard was hit by lightning. No grounds. Keel on wood blocks and the hull stabilized by jack stands. Lightning hit and blew two holes (2-3") next to the jack stands to get to ground. The mast was probably 70' above sea level. Boats in the water 50 yards away with bonded grounded masts were not touched. Go Figure. Bill
A few years ago. A Hunter 42 which was out of the water at the yard was hit by lightning. No grounds. Keel on wood blocks and the hull stabilized by jack stands. Lightning hit and blew two holes (2-3") next to the jack stands to get to ground. The mast was probably 70' above sea level. Boats in the water 50 yards away with bonded grounded masts were not touched. Go Figure.
Billlightning hits.
We ahve had several hits on boats in our mooring area with different kinds of boats and rigs. the most hit boat was hit 4 times that i know of. 3 times in 3 weeks. the last exploded the wood epoxy mast. this boat was not bonded. but current traveled down the mast to the fiberglass beam (catamaran) then it jumped to the water. previously it was hit while grounded in the same way. on two of the hits, current came down the wireing for the running lights. burned out the lights and ran down a wire where the battery normally was installed. It was not hooked up the current then blew about 15 small holes thru the hull laminate. Cored e-glass and alowed the boat to sink. not once but three times. we found electrical damage to the hull every where the wire turned on a radius. We live in the hottest lightning area in the U.S. i think. west florida. Bonded boats get hit as well as non bonded. On a trip the the abacos on a 43 footer we took a direct hit to the mast. boat was unbonded. took out all electronics blew up the electric pannel resulting i severe shock to one of the crew.( knocked him unconcious) He woke in moments and is fine. We Sailed the boat back to miami using flashlights for running lights, there was no damage to the hull or structure. just the electrical system, instruments radios, ect. thank god for a handheld gps. made getting home easier. My experience is if its your time your going to get hit. and there is not a hell of a lot you can do about it.
We ahve had several hits on boats in our mooring area with different kinds of boats and rigs. the most hit boat was hit 4 times that i know of. 3 times in 3 weeks. the last exploded the wood epoxy mast. this boat was not bonded. but current traveled down the mast to the fiberglass beam (catamaran) then it jumped to the water. previously it was hit while grounded in the same way. on two of the hits, current came down the wireing for the running lights. burned out the lights and ran down a wire where the battery normally was installed. It was not hooked up the current then blew about 15 small holes thru the hull laminate. Cored e-glass and alowed the boat to sink. not once but three times. we found electrical damage to the hull every where the wire turned on a radius. We live in the hottest lightning area in the U.S. i think. west florida. Bonded boats get hit as well as non bonded. On a trip the the abacos on a 43 footer we took a direct hit to the mast. boat was unbonded. took out all electronics blew up the electric pannel resulting i severe shock to one of the crew.( knocked him unconcious) He woke in moments and is fine. We Sailed the boat back to miami using flashlights for running lights, there was no damage to the hull or structure. just the electrical system, instruments radios, ect. thank god for a handheld gps. made getting home easier. My experience is if its your time your going to get hit. and there is not a hell of a lot you can do about it.
jumper cables and grounding plates
At one time I was very concerned with lightning. I made up two heavy cables with aluminum plates at the end. These cables were bare for a foot or so and I wrapped them one to a side around the mast above the boom to try and turn the electricity gently. I also connected a cable to the backstay and ran it directly into the water. On stormy nights I deployed this system as it wouldn't work while sailing. Supposedly the plates need to be larger in fresh water as it doesn't conduct as well. Also a rectangular plate works better than a square or round plate. I also tried to anchor deep in a cove surrounded by trees. Fortunately this system was never put to the test. I started thinking about the boat sitting at the dock year round without being struck. Then decided the odds were in my favor. What's the old saying ???" A coward dies a thousand times and the brave(stupid) only once". But seriously if you worry too much about what might happen life sucks even if it is a longer life. Finding a happy middle ground where you avoid real high probablity risks and don't worry too much about what ifs is hard.
At one time I was very concerned with lightning. I made up two heavy cables with aluminum plates at the end. These cables were bare for a foot or so and I wrapped them one to a side around the mast above the boom to try and turn the electricity gently. I also connected a cable to the backstay and ran it directly into the water. On stormy nights I deployed this system as it wouldn't work while sailing. Supposedly the plates need to be larger in fresh water as it doesn't conduct as well. Also a rectangular plate works better than a square or round plate. I also tried to anchor deep in a cove surrounded by trees. Fortunately this system was never put to the test. I started thinking about the boat sitting at the dock year round without being struck. Then decided the odds were in my favor. What's the old saying ???" A coward dies a thousand times and the brave(stupid) only once". But seriously if you worry too much about what might happen life sucks even if it is a longer life. Finding a happy middle ground where you avoid real high probablity risks and don't worry too much about what ifs is hard.
Once Again
Around the first part of July this year, lightning struck the mast of a boat at the end of the pier, almost blew the hull apart, but it didn't sink. Seven other boats berthed in it's vicinity, including mine, received damage, mostly electronics to include a couple of inverters. Of all of the boats that received damage, some were bonded, some not. As of this date, we still haven't figured out exactly what happened. We are not sure if the charge came up through our through hulls, through the shore power, or just residual effects. I have seen several opinions relative to lightning in these posts, and they all depending on the particular circumstance might be right. What I do know for a fact is that lightning is unpredictable and it pretty much does whatever it wants to. There is nothing that anyone can do about it to a certainty. The debate goes on!!
Around the first part of July this year, lightning struck the mast of a boat at the end of the pier, almost blew the hull apart, but it didn't sink. Seven other boats berthed in it's vicinity, including mine, received damage, mostly electronics to include a couple of inverters. Of all of the boats that received damage, some were bonded, some not. As of this date, we still haven't figured out exactly what happened. We are not sure if the charge came up through our through hulls, through the shore power, or just residual effects. I have seen several opinions relative to lightning in these posts, and they all depending on the particular circumstance might be right. What I do know for a fact is that lightning is unpredictable and it pretty much does whatever it wants to. There is nothing that anyone can do about it to a certainty. The debate goes on!!
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