Has anybody installed lightning protection on their Mac 26? I have been doing research on the subject and have come up with 3 options: 1. Ewen Thompon did a study in 1992 - Florida Sea Grant College Program He concludes that the mast should be grounded. 2. William Becker, University of Florida, also in 1992 concluded that grounding the mast increased the chance of lightning strike. 3. Arlyn Stewart questioned some of Ewen Thomson's conclusions in 2003. Arlyn is not convinced that grounding the mast is a good thing. He beleives that a length of welding cable is best. The cable is wrapped around the base of the mast a couple of times. The insulation is left on the cable except for that portion draped over each side and placed in the water for ground. The insulation on that portion around the mast has holes in the insulation. This way the mast is not grounded, but if a strike occurs, the energy from the mast will find the holes in the insulation and follow the path to ground. Any comments, ideas or experiences? Thanks, Jerry
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D
Dan McGuire
Surprised There Have Not Been More Comments
This has been a hot subject in the past. I believe the consensus is that grounding the mast does not significantly change the chances of a lightning strike. Someone else is probably better qualified to tell you why. That being the case, it is important to channel the charge so that the damage to the boat is minimized. I attach some old jumper cables to one of the shrouds and drop the other end in the water. I realize that this might burn the shroud in two, but for my MAC 23, the mast would not fall due to to failure of just one of the shrouds. There is a MAC 25 in Mountain View Arkansas which has been sitting in the yard for probably five or ten years. I stopped in to ask the owner, if he wanted to sell it. He was not interested, but there were burn holes in the fiberglass at the water line caused by a lightning strike.
This has been a hot subject in the past. I believe the consensus is that grounding the mast does not significantly change the chances of a lightning strike. Someone else is probably better qualified to tell you why. That being the case, it is important to channel the charge so that the damage to the boat is minimized. I attach some old jumper cables to one of the shrouds and drop the other end in the water. I realize that this might burn the shroud in two, but for my MAC 23, the mast would not fall due to to failure of just one of the shrouds. There is a MAC 25 in Mountain View Arkansas which has been sitting in the yard for probably five or ten years. I stopped in to ask the owner, if he wanted to sell it. He was not interested, but there were burn holes in the fiberglass at the water line caused by a lightning strike.
B
Blake
jumper cables
I use the same method as Dan. Jumper cables are easy, hope I never find out if they work.
I use the same method as Dan. Jumper cables are easy, hope I never find out if they work.
W
walt
jumper cable method
One other point about the jumper cables.. I think if you do use jumper cables (probably better than the chain idea), I would think it would be better to clamp to the mast. The reason again has to do with inductance. In the case of the side stay having the cable attached and in the water, if lightning stikes, the whole mast and stay structure will become charged up. Initally the water has a high impedance so basically the mast and stays have about the same voltage potential. The cable in the water is likely to initialize the discharge and when this happens, there become a low impedance path to the water. However, what you have electrically is a fairly high inductance stay up to the mast and this will still allow the mast to rise to a very high voltage even with the discharge occuring at the stay. When the mast gets to a high potential, the same exact mechanism of the side discharging that created the holes in the hull right above water line could still happen. A human body sitting inside the cabin is a fairly good conductor and will also cause electric field distortions - ie, a body makes a nice "short cut" for the discharge from the bottom of the mast to the water surface. If you connect instead the cables to the mast, the cables are still likely to have the first inital discharge to the water but now hopefully you have a low inductance path right to the main conductor which is charged up. If you can discharge the mast, you would have less to worry about with the stays. Is this good advice, I really dont know. But I personally would connect the jumper cables right to the mast instead of the stays and get the largest guage cables you can.
One other point about the jumper cables.. I think if you do use jumper cables (probably better than the chain idea), I would think it would be better to clamp to the mast. The reason again has to do with inductance. In the case of the side stay having the cable attached and in the water, if lightning stikes, the whole mast and stay structure will become charged up. Initally the water has a high impedance so basically the mast and stays have about the same voltage potential. The cable in the water is likely to initialize the discharge and when this happens, there become a low impedance path to the water. However, what you have electrically is a fairly high inductance stay up to the mast and this will still allow the mast to rise to a very high voltage even with the discharge occuring at the stay. When the mast gets to a high potential, the same exact mechanism of the side discharging that created the holes in the hull right above water line could still happen. A human body sitting inside the cabin is a fairly good conductor and will also cause electric field distortions - ie, a body makes a nice "short cut" for the discharge from the bottom of the mast to the water surface. If you connect instead the cables to the mast, the cables are still likely to have the first inital discharge to the water but now hopefully you have a low inductance path right to the main conductor which is charged up. If you can discharge the mast, you would have less to worry about with the stays. Is this good advice, I really dont know. But I personally would connect the jumper cables right to the mast instead of the stays and get the largest guage cables you can.
W
walt
To ground or not ground
Speaking directly out of my a_s now... please feel free to correct things I have read (maybe understood a little) or Dr Thomson stuff, have not other papers on grounding a mast or not. In my opionion, we should consider two items regarding the effect of grounding or not grounding a mast. First, does mast grounding affect the chances of a downcomming lighting strike from picking the mast vs. going somewhere else and second, is the grounded mast effective in creating upwards loss leaders. (a loss leader is basically charge flowing from the earth that goes up to meet the downcomming charge. Something which can initiate a loss leader is definalty more likely to take a strike). Electric fields affect the path lightning is likely to take. A conductor placed "normal" to an electric field will take on the voltage potential of its midpoint. For example, if at height 0, the voltage is 0 and at 10 meters, the voltage is 1E6 volts (ie, the electric field gradient is 1E5 volts/meter) and an insulated conductor is placed in this field so is oriented up/down, the entire conductor will take on the voltage of its midpoint at 5 meters which is 0.5E6 volts. At the top of the conductor, the free field potential would have been 1E6 but since the top of the mast is at .5E6, there is a distortion in the electric field and also, the electric field has been concentrated at the top of the conductor(or mast). However, if the conductor is now grounded, the whole conductor has a potential of 0 volts. So at its top which is also at 0 volts, the distortion to the free field is now the full 1E6 volts. Ie, there is more field distortion and concentration with the grounded conductor (or mast as in our case). There is a good chance that this higher field distortion increases the odds of attracting a strike. But, I would guess its such a small number and probably insignificant. The next part is really pure speculation on my part but could a grounded mast affect the generation of a loss leader? I think it wont make a bit of difference. It seems that water (particurly fresh water) would have a hard time generating a loss leader in the first place but somehow a cloud does it. In the cloud, why the charges are kept together I dont know (gravity?) but when they get concentrated enough (probably aided by being attracted to earth), at some point, the charge concentration causes a local ionization to occur. If there is charge available to dump into the ionization, it will begin to propogate because just as in the conductor case, the propogating ionization will tend to concetrate the electric field at either end so will grow. The propogating ionization can keep on going as long as there is the charge availabe to keep ohms law working and sustain the electric field necessary for the ionization to exist in the first place. So can water initialize a local ionization and have enough charge available to sustain its flow upwards. I would guess not and my complete pulled out of my butt guess is that water does not have the mechanism to concentrate charges that a cloud does (really have no idea..). Ie, the body of water is electically connected to the "planet". But if there was a mechanism in the water to initialize the local ionization and it had the charge available to sustain it, a little air such as a spark gap under the mast is just not going to make any difference. If the spark gap mattered, there probably isnt enough charge available for the loss leader to go anywhere anyhow. So basically, I think having jumper cables in the water and connected to the mast adds virtually no risk of attracting a stike. And I dont think there is anything wrong about relying on a spark gap as part of the discharge for the mast. As always, Im not an expert on this so take if for what it is - just another post on the internet.
Speaking directly out of my a_s now... please feel free to correct things I have read (maybe understood a little) or Dr Thomson stuff, have not other papers on grounding a mast or not. In my opionion, we should consider two items regarding the effect of grounding or not grounding a mast. First, does mast grounding affect the chances of a downcomming lighting strike from picking the mast vs. going somewhere else and second, is the grounded mast effective in creating upwards loss leaders. (a loss leader is basically charge flowing from the earth that goes up to meet the downcomming charge. Something which can initiate a loss leader is definalty more likely to take a strike). Electric fields affect the path lightning is likely to take. A conductor placed "normal" to an electric field will take on the voltage potential of its midpoint. For example, if at height 0, the voltage is 0 and at 10 meters, the voltage is 1E6 volts (ie, the electric field gradient is 1E5 volts/meter) and an insulated conductor is placed in this field so is oriented up/down, the entire conductor will take on the voltage of its midpoint at 5 meters which is 0.5E6 volts. At the top of the conductor, the free field potential would have been 1E6 but since the top of the mast is at .5E6, there is a distortion in the electric field and also, the electric field has been concentrated at the top of the conductor(or mast). However, if the conductor is now grounded, the whole conductor has a potential of 0 volts. So at its top which is also at 0 volts, the distortion to the free field is now the full 1E6 volts. Ie, there is more field distortion and concentration with the grounded conductor (or mast as in our case). There is a good chance that this higher field distortion increases the odds of attracting a strike. But, I would guess its such a small number and probably insignificant. The next part is really pure speculation on my part but could a grounded mast affect the generation of a loss leader? I think it wont make a bit of difference. It seems that water (particurly fresh water) would have a hard time generating a loss leader in the first place but somehow a cloud does it. In the cloud, why the charges are kept together I dont know (gravity?) but when they get concentrated enough (probably aided by being attracted to earth), at some point, the charge concentration causes a local ionization to occur. If there is charge available to dump into the ionization, it will begin to propogate because just as in the conductor case, the propogating ionization will tend to concetrate the electric field at either end so will grow. The propogating ionization can keep on going as long as there is the charge availabe to keep ohms law working and sustain the electric field necessary for the ionization to exist in the first place. So can water initialize a local ionization and have enough charge available to sustain its flow upwards. I would guess not and my complete pulled out of my butt guess is that water does not have the mechanism to concentrate charges that a cloud does (really have no idea..). Ie, the body of water is electically connected to the "planet". But if there was a mechanism in the water to initialize the local ionization and it had the charge available to sustain it, a little air such as a spark gap under the mast is just not going to make any difference. If the spark gap mattered, there probably isnt enough charge available for the loss leader to go anywhere anyhow. So basically, I think having jumper cables in the water and connected to the mast adds virtually no risk of attracting a stike. And I dont think there is anything wrong about relying on a spark gap as part of the discharge for the mast. As always, Im not an expert on this so take if for what it is - just another post on the internet.
B
Bill
Death Rate?
Anybody have any idea the number of lightening strike deaths per year for persons on sailboats?? I have never personally heard of one or perhaps, did not want to hear of one.
Anybody have any idea the number of lightening strike deaths per year for persons on sailboats?? I have never personally heard of one or perhaps, did not want to hear of one.
W
walt
my data
Im not sure about the rest of the world but my sailing spot is in Colorado at about 8600 feet (Elevenmile) and in July and August, the lake normally gets a daily thunder storm. Its a great place for fishing so there are always a fair amount of boats on it (mostly outboard aluminum) The water is very clean (ie, very high impedance). Ive talked to several old timers at this lake and no one can remember a boat getting struck by lightning (this is in about 25 years). However, people have been struck by lighting on the shore. People generally try and come in when a storm brews up but because everyone tries to come in at the same time, you usually end up stuck out on the lake or you are getting out of the water at just the worst possible time. However, in the Denver area, boats have been struck by lighting but as far as I know, it always happened when they were in a slip with no one in the boats. Slips are near shore, the water is shallow and I dont know if the boats were plugged into shore power or not. What happens with a nicely grounded boat plugged into and grounded with shore power is a different subject. I have heard of several cases of windsurfers getting struck by lightning. The strike goes down the mast and jumps to the water through the board. It destroys the rig but I dont think any of the sailors were seriously injured. I overall think the risk of a strike is very low but I often have some familly with me in the sail boat. I can afford to lose the sailboat but not the familly..
Im not sure about the rest of the world but my sailing spot is in Colorado at about 8600 feet (Elevenmile) and in July and August, the lake normally gets a daily thunder storm. Its a great place for fishing so there are always a fair amount of boats on it (mostly outboard aluminum) The water is very clean (ie, very high impedance). Ive talked to several old timers at this lake and no one can remember a boat getting struck by lightning (this is in about 25 years). However, people have been struck by lighting on the shore. People generally try and come in when a storm brews up but because everyone tries to come in at the same time, you usually end up stuck out on the lake or you are getting out of the water at just the worst possible time. However, in the Denver area, boats have been struck by lighting but as far as I know, it always happened when they were in a slip with no one in the boats. Slips are near shore, the water is shallow and I dont know if the boats were plugged into shore power or not. What happens with a nicely grounded boat plugged into and grounded with shore power is a different subject. I have heard of several cases of windsurfers getting struck by lightning. The strike goes down the mast and jumps to the water through the board. It destroys the rig but I dont think any of the sailors were seriously injured. I overall think the risk of a strike is very low but I often have some familly with me in the sail boat. I can afford to lose the sailboat but not the familly..
S
Steve Paul
Don't mess with it
I heartily recommend the same book I always do, "The Boatowner's Mechanical and Electrical manual" by Nigel Calder. His chapter on lightning is thorough and explains for both the professional and non-professional the many known aspects of lightning discharge and their effect on boats. One of the important topics is to recognize that electricity at these voltages and currents is mostly unpredictable and one should never forget that. I spent many years in the cable and television industry where lightning is a fact of life. There are millions of lightning strikes every day around the world and that is one of the contributors to background radio noise. Most of us are trailer sailors with deck mounted masts but keep in mind that keel stepped masts are more easily grounded and present less of a damage problem. The idea with lightning is to avoid the situation where it is a problem. That said; there are things we can do to reduce the electron build up on our masts and boats. Ion eliminators or fuzzy shrouds mounted high on the mast do a good job of bleeding off the charge during storms and this directly reduces the likelyhood of a direct strike. Bonding the rigging, motor and metal parts is paramount to spreading the charge and avoiding blowing a hole in your boat. We've had two lightning sinkings on our lake in the last 10 years and neither were bonded boats. Both of them had large holes blown in the hull where the lightning found the shortest path to fresh water. Fresh water by the way is more dangerous than salt water ad it's conductivity is less and the charge will tend to congregate rather than dissipate. We've had several deaths in aluminum fishing boats from lightning where the owner had one hand on the motor and was heading in to get out of the storm. The passengers were unharmed but the motor operator was fried from being part of the conductor. I think the short of it is to be aware this is a problem, lightning is unpredictable at best but there are measures that can be used to reduce the risk while on board. Stay away from the rigging, avoid the area under the mast and don't touch any metal parts during a storm or just before the storm as the charge on your boat starts to increase. A properly grounded and bonded boat will present an umbrella of safey or cone of safey but where ligtning is concerned there is no guarantee or predictability as to when or where it will strike. I hope this helps and do read the book, it is extremely helpful. Steve P.
I heartily recommend the same book I always do, "The Boatowner's Mechanical and Electrical manual" by Nigel Calder. His chapter on lightning is thorough and explains for both the professional and non-professional the many known aspects of lightning discharge and their effect on boats. One of the important topics is to recognize that electricity at these voltages and currents is mostly unpredictable and one should never forget that. I spent many years in the cable and television industry where lightning is a fact of life. There are millions of lightning strikes every day around the world and that is one of the contributors to background radio noise. Most of us are trailer sailors with deck mounted masts but keep in mind that keel stepped masts are more easily grounded and present less of a damage problem. The idea with lightning is to avoid the situation where it is a problem. That said; there are things we can do to reduce the electron build up on our masts and boats. Ion eliminators or fuzzy shrouds mounted high on the mast do a good job of bleeding off the charge during storms and this directly reduces the likelyhood of a direct strike. Bonding the rigging, motor and metal parts is paramount to spreading the charge and avoiding blowing a hole in your boat. We've had two lightning sinkings on our lake in the last 10 years and neither were bonded boats. Both of them had large holes blown in the hull where the lightning found the shortest path to fresh water. Fresh water by the way is more dangerous than salt water ad it's conductivity is less and the charge will tend to congregate rather than dissipate. We've had several deaths in aluminum fishing boats from lightning where the owner had one hand on the motor and was heading in to get out of the storm. The passengers were unharmed but the motor operator was fried from being part of the conductor. I think the short of it is to be aware this is a problem, lightning is unpredictable at best but there are measures that can be used to reduce the risk while on board. Stay away from the rigging, avoid the area under the mast and don't touch any metal parts during a storm or just before the storm as the charge on your boat starts to increase. A properly grounded and bonded boat will present an umbrella of safey or cone of safey but where ligtning is concerned there is no guarantee or predictability as to when or where it will strike. I hope this helps and do read the book, it is extremely helpful. Steve P.
W
walt
hope you dont mind my questions..
Steve, hope you dont take this at all wrong, I think the original intention of the poster was to bring up a debate.. so I would like to debate. "Ion eliminators or fuzzy shrouds mounted high on the mast do a good job of bleeding off the charge during storms and this directly reduces the likelyhood of a direct strike." Do you have any references for this. Most of the experts will disagree that these have much affect at all and there is plenty of evidence that boats get struck which have them. Im an electrical engineer but not an expert in lighting and they make no sense to me - which is why Im wondering what your reference is. Ill look for my references also. "Fresh water by the way is more dangerous than salt water ad it's conductivity is less and the charge will tend to congregate rather than dissipate." Once again, references on why is this true. I also dont think that "charge congregating rather than disipating" has anything to do with it. However, if you read the radials paper I gave the reference for earlier, it points out that the surface charging of fresh water takes much longer than for salt water. This additional time delay is why fresh water can allow higher voltage buildups and stronger side flash discharges. "A properly grounded and bonded boat will present an umbrella of safey or cone of safey" This is true, but all the Macs have almost no grounding or bonding whatsoever (either does any of the smaller Catalina's, dont know about the bigger ones). You can see here what a grounded and bonded boat looks like http://www.marinelightning.com/science.htm#Solutions There is no way my Mac is ever going to look like that. I would also be curious if you had any more detail about the two boats which had holes blown in them. Ie, were they sailing, moored, slipped, if slipped, was there a grounded power connection? I completely agree about avoiding lighting. However, in the next breath, I would also have to say that often enough lighting stikes with almost no warning that it was comming.. Hopefully also on anything I wrote, I either had some sort of reference or told you I was pulling it out of my axx. Last summer, there was a thread on lighting where I posted some wrong stuff but had some good discussion and learned some things. Hopefully that is also our intention here.
Steve, hope you dont take this at all wrong, I think the original intention of the poster was to bring up a debate.. so I would like to debate. "Ion eliminators or fuzzy shrouds mounted high on the mast do a good job of bleeding off the charge during storms and this directly reduces the likelyhood of a direct strike." Do you have any references for this. Most of the experts will disagree that these have much affect at all and there is plenty of evidence that boats get struck which have them. Im an electrical engineer but not an expert in lighting and they make no sense to me - which is why Im wondering what your reference is. Ill look for my references also. "Fresh water by the way is more dangerous than salt water ad it's conductivity is less and the charge will tend to congregate rather than dissipate." Once again, references on why is this true. I also dont think that "charge congregating rather than disipating" has anything to do with it. However, if you read the radials paper I gave the reference for earlier, it points out that the surface charging of fresh water takes much longer than for salt water. This additional time delay is why fresh water can allow higher voltage buildups and stronger side flash discharges. "A properly grounded and bonded boat will present an umbrella of safey or cone of safey" This is true, but all the Macs have almost no grounding or bonding whatsoever (either does any of the smaller Catalina's, dont know about the bigger ones). You can see here what a grounded and bonded boat looks like http://www.marinelightning.com/science.htm#Solutions There is no way my Mac is ever going to look like that. I would also be curious if you had any more detail about the two boats which had holes blown in them. Ie, were they sailing, moored, slipped, if slipped, was there a grounded power connection? I completely agree about avoiding lighting. However, in the next breath, I would also have to say that often enough lighting stikes with almost no warning that it was comming.. Hopefully also on anything I wrote, I either had some sort of reference or told you I was pulling it out of my axx. Last summer, there was a thread on lighting where I posted some wrong stuff but had some good discussion and learned some things. Hopefully that is also our intention here.
W
walt
more on the jumper cable idea
Just a few more thoughts (I dont claim them to be accurate) on the battery jumper cable idea. First, I think connecting to the mast is going to be a much better idea than the stays and its because of the inductance of the stays are likely too high(see the description earlier and we could discuss this more - I have some more references on this). However, masts are anodized aluminum and if you have ever put an ohm meter on one, you pretty much will measure no conductivity. The stainless steel base that the mast sits on however is conductive and generally will be conductive to the mast through the bold but its a little bit scary. I wonder about bolting something copper on the bottom of the mast for the jumper cables to bite into. For the jumper cable idea to work, the cable must be both low inductance and the cable also must make a very good elecrical connection to the mast.. The other thing is that when "grounding plates" (used to disipate the charge on the bottom of boats) are recomenened, I beleive (this could be inaccurate) that they are recomended to be at least 1 foot square. Of course the ends of the jumper cable are not one foot square. However, this may not matter (my opinion). The link (you may have to cut and past, I see my links are getting broken by the BB software) below shows basically what Dr. Thomson patented: http://www.marinelightning.com/Siedarc.htm The siedarc conductors do not have 1 foot square ground plates. However, I think they would be effective because they are oriented "normal" to the electric field. Ie, if the field gradient is up/down, and a conductor is placed in the field so that it is up/down, the conductor will take on its mid point voltage and will concentrate the fields at either end. Concentrating the field is what iniatiates the dishcharge. Interesting also is that a ground plate which is bonded to the flat underside of a boat is in the "possibly" worst orientation with respect to the likely electric field. So the jumper cables over the side are more than likely in a good orientation so concentrate the electric field. In fact (also read more on the Siedarc web site), the ends of the cables dont even need to be in the water - but they should be as low as possible. For someone who doesnt like the idea of a grounded mast, this might be a good option for them. Once again, I am very leary of the cables actually working and its mostly because of thier inductance. However, keep in mind this is only discussion and not advice on how to make them actually work..
Just a few more thoughts (I dont claim them to be accurate) on the battery jumper cable idea. First, I think connecting to the mast is going to be a much better idea than the stays and its because of the inductance of the stays are likely too high(see the description earlier and we could discuss this more - I have some more references on this). However, masts are anodized aluminum and if you have ever put an ohm meter on one, you pretty much will measure no conductivity. The stainless steel base that the mast sits on however is conductive and generally will be conductive to the mast through the bold but its a little bit scary. I wonder about bolting something copper on the bottom of the mast for the jumper cables to bite into. For the jumper cable idea to work, the cable must be both low inductance and the cable also must make a very good elecrical connection to the mast.. The other thing is that when "grounding plates" (used to disipate the charge on the bottom of boats) are recomenened, I beleive (this could be inaccurate) that they are recomended to be at least 1 foot square. Of course the ends of the jumper cable are not one foot square. However, this may not matter (my opinion). The link (you may have to cut and past, I see my links are getting broken by the BB software) below shows basically what Dr. Thomson patented: http://www.marinelightning.com/Siedarc.htm The siedarc conductors do not have 1 foot square ground plates. However, I think they would be effective because they are oriented "normal" to the electric field. Ie, if the field gradient is up/down, and a conductor is placed in the field so that it is up/down, the conductor will take on its mid point voltage and will concentrate the fields at either end. Concentrating the field is what iniatiates the dishcharge. Interesting also is that a ground plate which is bonded to the flat underside of a boat is in the "possibly" worst orientation with respect to the likely electric field. So the jumper cables over the side are more than likely in a good orientation so concentrate the electric field. In fact (also read more on the Siedarc web site), the ends of the cables dont even need to be in the water - but they should be as low as possible. For someone who doesnt like the idea of a grounded mast, this might be a good option for them. Once again, I am very leary of the cables actually working and its mostly because of thier inductance. However, keep in mind this is only discussion and not advice on how to make them actually work..
W
walt
an easy idea
Just one more idea (easiest of them all..) This was pulled from Steve's post which I think is very good advice: "Stay away from the rigging, avoid the area under the mast and don't touch any metal parts during a storm or just before the storm" I can see myself trying to tell the kids to stay away from under the mast and stays when all hell is breaking loose and Im not sure they even know what a stay is (and I dont know exactly where they are from inside the boat). The idea was to put some sort of subtle marking on the inside of the cabin which either said to keep in this area or keep out of that area in a lightning storm. So if you did get in a hairy situation, you could just tell guests or crew to stay away from the areas inside the cabin marked with the "chicken smoldering on the rotisserie" signs.
Just one more idea (easiest of them all..) This was pulled from Steve's post which I think is very good advice: "Stay away from the rigging, avoid the area under the mast and don't touch any metal parts during a storm or just before the storm" I can see myself trying to tell the kids to stay away from under the mast and stays when all hell is breaking loose and Im not sure they even know what a stay is (and I dont know exactly where they are from inside the boat). The idea was to put some sort of subtle marking on the inside of the cabin which either said to keep in this area or keep out of that area in a lightning storm. So if you did get in a hairy situation, you could just tell guests or crew to stay away from the areas inside the cabin marked with the "chicken smoldering on the rotisserie" signs.
J
Jerry
Thanks for all the great info
Walt, I like your ideas. And the debate has served to increase my understanding of a highly controversial subject. I can find the #2 Wally Wire. Could you describe lug for the mast and the 3 clamps. I sure don't fully grasp the physics, but I think what you describe in simple terms offers a strike that hits the mast the easiest route to where it naturally wants to go, without going through the hull or sparking out. Please feel free to correct me if I'm off here. From the posts I get: 1. Stay out of harms way - listen to the weather radio and watch the sky. If storms are predicted, stay in port. If you are out sailing and a storm approaches try to avoid by running away. 2. Stay away from the mast, shrouds and all metal if you get caught in a storm. I guess the aft berth would be the best place on the boat. 3. If a storm is approaching and you cannot successfully ran away, deploy Walt's Wally Wire system and hunker down. I guess dropping the hook and heading for the aft berth. I believe my chances of getting run down by a crazy on I95 are much greater than being hurt by lightning on a sailboat. However, it doesn't hurt to be like a boy scout. Jerry
Walt, I like your ideas. And the debate has served to increase my understanding of a highly controversial subject. I can find the #2 Wally Wire. Could you describe lug for the mast and the 3 clamps. I sure don't fully grasp the physics, but I think what you describe in simple terms offers a strike that hits the mast the easiest route to where it naturally wants to go, without going through the hull or sparking out. Please feel free to correct me if I'm off here. From the posts I get: 1. Stay out of harms way - listen to the weather radio and watch the sky. If storms are predicted, stay in port. If you are out sailing and a storm approaches try to avoid by running away. 2. Stay away from the mast, shrouds and all metal if you get caught in a storm. I guess the aft berth would be the best place on the boat. 3. If a storm is approaching and you cannot successfully ran away, deploy Walt's Wally Wire system and hunker down. I guess dropping the hook and heading for the aft berth. I believe my chances of getting run down by a crazy on I95 are much greater than being hurt by lightning on a sailboat. However, it doesn't hurt to be like a boy scout. Jerry
W
walt
clamps???
The "Wally Wire" idea I beleive is new (since about 3:30 PM today)so Im not sure of exactly how to do it or what problem you would run into implementing it (like the wires not hanging down over the edge of the boat or ??). The goal is to make a very good low impedance connection to the mast and be able to do it quickly as you dont want to spend a lot of time near the base of the mast if its about to get zapped. The big aligator clamps on battery cables might OK (is there anything better than this you can get at a hardware store - small, tight, lots of surface area) and you can not clamp directly to the mast as it is anodized aluminum and not conductive. So I was thinking maybe a block of copper could be bolted to the mast. Multiple bolts would hopefully make a good connection between the mast and the copper block. The copper block would have to be out of the way when the mast dropped so maybe on the front would be better. It would just sit there doing nothing until you clamped the "wally wire" to it. I think the stays would be easier to clamp to since its all stainless hardware. Maybe once again, use something like a battery cable aligator clamp I think it also might be worth looking into ways to decrease the inductance of the wire as this could be key in having it do anything. Things like this are also only about "possibly" reducing risks and not eliminating them. But I like this implementation and think it could be worth doing - and you can always just throw it out if you sell the boat.. Maybe this idea is questionable and not worth pursuing but any other ideas on the mast clamping??
The "Wally Wire" idea I beleive is new (since about 3:30 PM today)so Im not sure of exactly how to do it or what problem you would run into implementing it (like the wires not hanging down over the edge of the boat or ??). The goal is to make a very good low impedance connection to the mast and be able to do it quickly as you dont want to spend a lot of time near the base of the mast if its about to get zapped. The big aligator clamps on battery cables might OK (is there anything better than this you can get at a hardware store - small, tight, lots of surface area) and you can not clamp directly to the mast as it is anodized aluminum and not conductive. So I was thinking maybe a block of copper could be bolted to the mast. Multiple bolts would hopefully make a good connection between the mast and the copper block. The copper block would have to be out of the way when the mast dropped so maybe on the front would be better. It would just sit there doing nothing until you clamped the "wally wire" to it. I think the stays would be easier to clamp to since its all stainless hardware. Maybe once again, use something like a battery cable aligator clamp I think it also might be worth looking into ways to decrease the inductance of the wire as this could be key in having it do anything. Things like this are also only about "possibly" reducing risks and not eliminating them. But I like this implementation and think it could be worth doing - and you can always just throw it out if you sell the boat.. Maybe this idea is questionable and not worth pursuing but any other ideas on the mast clamping??
W
walt
The importance of low inductance
(from R.T. Hasbrooch, EE, PE) Regarding the importance of inductance Lightning, which is a current pulse, contains a broad spectrum of frequencies. The center of the power spectrum is about 4.5 kHz, with the upper limit reaching into the MHz range. Its peak return-stroke current is extremely large (10s of thousands of amperes), typically lasting for a hundred microseconds, or so. As the return-stroke current pulse flows through the resistance of the earth it produces a very large transient potential gradient across the ground. This potentially lethal gradient. Nominally 1,000 volts per meteris known as step voltage. However, even when the current is flowing in a substantial metallic conductor (i.e., one having a very low value of dc resistance) very large transient voltages are developed along the conductor. Although resistance may be very low, e.g., less than 10 ohms, the inductance (L) of the conductor (nominally 1.5 microhenrys per meter of conductor length) times the very high rate of change (di/dt) of the current pulse produces transient voltages reaching 100s of thousands volts, or higher (V = I*R + L* di/dt). So, despite the big emphasis on achieving a very low resistance ground, the inductive effect predominates, resulting in transient voltages significantly higher than those attributed to dc resistance of the grounding system. A lightning grounding system must be capable of accommodating extremely high peak currents, and present low values of resistance and inductance. When grounding system resistance is tested, the equipment operates at a very low frequency. The result, which may look quite low, will actually be just the dc resistance component. Huge (i.e., deadly and damaging) transient voltages will be developed across the conductor while return-stroke current is flowing. Finally, consider a ten-meter section of heavy copper conductor connected to an earth ground. For lightning protection, two systems are bonded to it, one at each end of the section. The dc resistance between the two points is measured to be ten milliohms; the inductance is 15 microhenrys. A 50th percentile lightning return stroke of 24-25 kA, with a current rate-of rise of 40 kA/microsecond, flows through the conductor. Peak current times dc resistance produces approximately a paltry 240 V peak between the two grounded points. However, the peak transient voltage resulting from the conductors inductance is 600,000 volts! The two supposedly grounded systems are 600 kV apart, albeit only for a brief interval of time. Equipment damage and serious injury or death are definite possibilities, hence the reason for using single-point grounding. (Some discussion regarding this..) Is there any hope on a trailer sailer? If our cable hanging off the mast is 5 meter long down to the water and we assume that the cable iniated a discharge into the water (which then makes the water a low impedance - how low dont know). If the inductance of the cable is the same as used above (ie, 15 uh for a 10 meter long wire), then we could assume our cable hanging over the side has an inductance of 7.5 uh. Using the same numers as above, the voltage developed at the driving end of the cable (which is the bottom end of the mast) is give by the same equation: V = L*dI/dT = 7.5uh * 40ka/1usec = 300,000 volts or 3E5 volts. Ie, the bottom of the mast would develope 3E5 volts because of the current transient and assuming a perfect ground from the water. The height of the mast above the water is about 1.5 meters. So in this case, the electric field between the mast and the water would be 3E5/1.5 meters = 2E5 volts per meter. If the air breakdown voltage for air occurs at over 1e6 volts/meter, maybe there is some hope of at least disipating some of the charge fron the wires over the side before there is major flashover from the bottom of the mast to the water (which could use a human body to aid getting to the water). Of course, a major problem with this model is it assumes the impedance at the water is zero which is not true and the error will result in higher voltages at the mast. The Thomson web site discusses what these impedances are but its some brain damage to read... (Im pretty sure I will regret writing this stuff some day as its probably all incorrect but what the heck, I dont expect any one to beleive it anyhow..)
(from R.T. Hasbrooch, EE, PE) Regarding the importance of inductance Lightning, which is a current pulse, contains a broad spectrum of frequencies. The center of the power spectrum is about 4.5 kHz, with the upper limit reaching into the MHz range. Its peak return-stroke current is extremely large (10s of thousands of amperes), typically lasting for a hundred microseconds, or so. As the return-stroke current pulse flows through the resistance of the earth it produces a very large transient potential gradient across the ground. This potentially lethal gradient. Nominally 1,000 volts per meteris known as step voltage. However, even when the current is flowing in a substantial metallic conductor (i.e., one having a very low value of dc resistance) very large transient voltages are developed along the conductor. Although resistance may be very low, e.g., less than 10 ohms, the inductance (L) of the conductor (nominally 1.5 microhenrys per meter of conductor length) times the very high rate of change (di/dt) of the current pulse produces transient voltages reaching 100s of thousands volts, or higher (V = I*R + L* di/dt). So, despite the big emphasis on achieving a very low resistance ground, the inductive effect predominates, resulting in transient voltages significantly higher than those attributed to dc resistance of the grounding system. A lightning grounding system must be capable of accommodating extremely high peak currents, and present low values of resistance and inductance. When grounding system resistance is tested, the equipment operates at a very low frequency. The result, which may look quite low, will actually be just the dc resistance component. Huge (i.e., deadly and damaging) transient voltages will be developed across the conductor while return-stroke current is flowing. Finally, consider a ten-meter section of heavy copper conductor connected to an earth ground. For lightning protection, two systems are bonded to it, one at each end of the section. The dc resistance between the two points is measured to be ten milliohms; the inductance is 15 microhenrys. A 50th percentile lightning return stroke of 24-25 kA, with a current rate-of rise of 40 kA/microsecond, flows through the conductor. Peak current times dc resistance produces approximately a paltry 240 V peak between the two grounded points. However, the peak transient voltage resulting from the conductors inductance is 600,000 volts! The two supposedly grounded systems are 600 kV apart, albeit only for a brief interval of time. Equipment damage and serious injury or death are definite possibilities, hence the reason for using single-point grounding. (Some discussion regarding this..) Is there any hope on a trailer sailer? If our cable hanging off the mast is 5 meter long down to the water and we assume that the cable iniated a discharge into the water (which then makes the water a low impedance - how low dont know). If the inductance of the cable is the same as used above (ie, 15 uh for a 10 meter long wire), then we could assume our cable hanging over the side has an inductance of 7.5 uh. Using the same numers as above, the voltage developed at the driving end of the cable (which is the bottom end of the mast) is give by the same equation: V = L*dI/dT = 7.5uh * 40ka/1usec = 300,000 volts or 3E5 volts. Ie, the bottom of the mast would develope 3E5 volts because of the current transient and assuming a perfect ground from the water. The height of the mast above the water is about 1.5 meters. So in this case, the electric field between the mast and the water would be 3E5/1.5 meters = 2E5 volts per meter. If the air breakdown voltage for air occurs at over 1e6 volts/meter, maybe there is some hope of at least disipating some of the charge fron the wires over the side before there is major flashover from the bottom of the mast to the water (which could use a human body to aid getting to the water). Of course, a major problem with this model is it assumes the impedance at the water is zero which is not true and the error will result in higher voltages at the mast. The Thomson web site discusses what these impedances are but its some brain damage to read... (Im pretty sure I will regret writing this stuff some day as its probably all incorrect but what the heck, I dont expect any one to beleive it anyhow..)
W
walt
while its interesting, it has some inacuracies
I wanted to point out some errors in my experiment. First, the instrument I used is for simulating ESD and not lighting and has an extremely fast rise and fall time - in the 10 nsec range. Note that lighting has a much slower rise and fall and frequency spectrum than this (in the order of Mhz to Khz). Given that the surface charging effects are time dependent, it is very possible that I wasnt seeing these. Second, my power level was also very low compared to lighting so I wouldnt have seen any of the water boiling effects - or who knows what other effects from very high energy levels. So at this point, I think its a much better idea to beleive what the Marinelightning guys did (ie, Dr. Thomson) - than what I did. I think still for this application (an easy to deploy system mainly focusing "attempting" to reduce side flashes from the mast), having a dishcarge electrode above and below water isnt a bad idea. Its still likely that the water surface is where the action is and if one of the electrodes does do anything, it also is not likely to hurt anything (unless of course you injure a fish while deploying it). If one of the discharge electrodes didnt work, it would sort of be like adding a high value resistor in parrellel with a low value resistor. You still get the impedance of the low value resistor.
I wanted to point out some errors in my experiment. First, the instrument I used is for simulating ESD and not lighting and has an extremely fast rise and fall time - in the 10 nsec range. Note that lighting has a much slower rise and fall and frequency spectrum than this (in the order of Mhz to Khz). Given that the surface charging effects are time dependent, it is very possible that I wasnt seeing these. Second, my power level was also very low compared to lighting so I wouldnt have seen any of the water boiling effects - or who knows what other effects from very high energy levels. So at this point, I think its a much better idea to beleive what the Marinelightning guys did (ie, Dr. Thomson) - than what I did. I think still for this application (an easy to deploy system mainly focusing "attempting" to reduce side flashes from the mast), having a dishcarge electrode above and below water isnt a bad idea. Its still likely that the water surface is where the action is and if one of the electrodes does do anything, it also is not likely to hurt anything (unless of course you injure a fish while deploying it). If one of the discharge electrodes didnt work, it would sort of be like adding a high value resistor in parrellel with a low value resistor. You still get the impedance of the low value resistor.
E
Ed
The Practical Side
I think Bill and Walt were on the right track. I have been around a lot of marinas and have never personally seen a sailboat damaged by lightning. I have sailrd in thunderstorms a few times (in Colorado) and my boat did not become a lighning rod. So, while the technical side of things so amply provided is interesting, it may not be especially relevant. The best advice is: 1. Try to stay out of sailboats in thunderstorms. VFR is best. 2. Stay away from stays, mast, booms, etc. when lightning is close. 3. Have good boat insurance just in case. Replacement value. 4. If you are really scared that lightning is a problem, hang jumper cables from the stays on both sides. Underwater, it would probably be good to have something metal to hang, rods, chains, etc. 5. If you get hit by lightning and live, please tell us here on this thread.
I think Bill and Walt were on the right track. I have been around a lot of marinas and have never personally seen a sailboat damaged by lightning. I have sailrd in thunderstorms a few times (in Colorado) and my boat did not become a lighning rod. So, while the technical side of things so amply provided is interesting, it may not be especially relevant. The best advice is: 1. Try to stay out of sailboats in thunderstorms. VFR is best. 2. Stay away from stays, mast, booms, etc. when lightning is close. 3. Have good boat insurance just in case. Replacement value. 4. If you are really scared that lightning is a problem, hang jumper cables from the stays on both sides. Underwater, it would probably be good to have something metal to hang, rods, chains, etc. 5. If you get hit by lightning and live, please tell us here on this thread.
W
walt
jumper cables on the stays... be careful..
Good advice except I would be very cautious about relying on the jumper cable on the side stay idea. In my opinion, it has a good chance of being useless. The simple models used here are probably not accurate but when they predict a potential problem, the actual problem could be much worse. Here is the quick and dirty technical mumbo-jumbo using what details I have.. take it for what it is, maybe only slightly accurate. Lets say the mast takes the strike (most likely) and the stay/jumper cable charges up and initiates a dishcharge. If we assume the dishcharge point (probably at the water surface) is best case perfect (probably a long way from being true), then the discharge from the mast to the water must account for the inductance of the stay and cable. The stay on a Mac is 20 foot long and close to 8 guage wire (.3uh/ft) and the jumper cable is about 4 foot at .25uh/ft. So the total inductance between the mast and the discharge is 20*.3 + 4*.25 = 21.55 uh Using the also simple model of V = L*dI/dT, where dI/dT = 40ka/usec, the voltage which would still develope at the bottom of the mast is 862K volts (just under 1 million volts). If the impedance of the discharge is not zero (and no way is it zero), we can add to this IR voltages at the discharge point. This is just too close to where the bottom of the mast will still have the discharges from the bottom of the mast to the nearest water line - I would not want to be using the head if this were to happen. Since the models might be wrong by a factor of 2 or 3 or more, and the actual voltages were much higher, YIKES... This is why Im going to bond directly to the bottom of the mast - but since the wires easilly go past the stays, also try and pick them up also.
Good advice except I would be very cautious about relying on the jumper cable on the side stay idea. In my opinion, it has a good chance of being useless. The simple models used here are probably not accurate but when they predict a potential problem, the actual problem could be much worse. Here is the quick and dirty technical mumbo-jumbo using what details I have.. take it for what it is, maybe only slightly accurate. Lets say the mast takes the strike (most likely) and the stay/jumper cable charges up and initiates a dishcharge. If we assume the dishcharge point (probably at the water surface) is best case perfect (probably a long way from being true), then the discharge from the mast to the water must account for the inductance of the stay and cable. The stay on a Mac is 20 foot long and close to 8 guage wire (.3uh/ft) and the jumper cable is about 4 foot at .25uh/ft. So the total inductance between the mast and the discharge is 20*.3 + 4*.25 = 21.55 uh Using the also simple model of V = L*dI/dT, where dI/dT = 40ka/usec, the voltage which would still develope at the bottom of the mast is 862K volts (just under 1 million volts). If the impedance of the discharge is not zero (and no way is it zero), we can add to this IR voltages at the discharge point. This is just too close to where the bottom of the mast will still have the discharges from the bottom of the mast to the nearest water line - I would not want to be using the head if this were to happen. Since the models might be wrong by a factor of 2 or 3 or more, and the actual voltages were much higher, YIKES... This is why Im going to bond directly to the bottom of the mast - but since the wires easilly go past the stays, also try and pick them up also.
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