I couldn't find a recent thread on lightning and sailboats, and have viewed the archives for "the usual" type of information on the topic. I've been thinking about lightning since getting caught in my new-to-me Mac25, single handed, in a vicious Labor Day storm under full sail on Cave Run Lake in Eastern Kentucky. The blue sky turned to black with very little warning (NOAA or otherwise), and within about 7 minutes, I found myself getting a heck of a sailing lesson while all of the power boats on the lake were racing past toward the dock. All I could think about as lightning struck the hillsides around me was (1) mast = lightning rod, and (2) where the phrase "curse like a sailer" came from. Since then, I've asked around the dock questions about lightning. There are about 120 sailboats slipped or moored near my boat, most staying in the water year 'round. Of all the people I asked, many of whom spend MUCH time around the lake, there was only one recollection of any lightning strike to a sailboat on the lake, and this was to a Hunter to which the owners had just added lightning protection for no particular reason. Within one week of the installation, the mast took a direct hit while the boat was in its slip, and two holes were blown through the side of the fiberglass hull just above the waterline on either side directly outboard of the mast. Makes me wonder, is anyone out there aware of actual incidents involving sailboats and lightning? Where did it happen? What were the circumstances? What kind of boat? (Mac25?!?) Crew hurt? Electronics damaged? Hull or other hardware damaged? Do some get struck and sustain no damage at all? I've felt relatively safe in my boat at anchor during storms. A little less so when under sail. But the odds seem pretty much in our favor as sailers given the number of storms that all of the boats appear to have safely weathered.
- Status
Best protection is good luck
I personally don't buy any of the lightning protection theories. And, nobody can knock me off that since there's no real research on the subject that I am aware of, just conjecture. All that stuff about grounding your boat and the so-called "cone of protection" is just wishful thinking, in my opinion. The fact is, most boats don't get hit by lightning because lightning doesn't hit most places. However, we all cling to wives-tales about the subject. Follow the "related link" to a sailnet article that covers the most popular myths pretty well.
I personally don't buy any of the lightning protection theories. And, nobody can knock me off that since there's no real research on the subject that I am aware of, just conjecture. All that stuff about grounding your boat and the so-called "cone of protection" is just wishful thinking, in my opinion. The fact is, most boats don't get hit by lightning because lightning doesn't hit most places. However, we all cling to wives-tales about the subject. Follow the "related link" to a sailnet article that covers the most popular myths pretty well.
Please check again
There are 78 fairly recent discussions on the topic of lightning in the archives.
There are 78 fairly recent discussions on the topic of lightning in the archives.
Lightning protection
Go to this site and read the story. It confirms my suspicion. Lightning is not attracted to boats. It is attracted to the people on the boats, some more than others. Regards, Dave
Go to this site and read the story. It confirms my suspicion. Lightning is not attracted to boats. It is attracted to the people on the boats, some more than others. Regards, Dave
Lot's of us have experience with lightning.
Let me tell my lightning story. (I don't make this stuff up.) When we pulled into Coasta Rica in '92, it was also the start of the rainy season. That should also read 'lightning season' For the entire summer our group of buddy boats were surrounded by lightning bolts hitting nearby. No one got hit. Then in passing, I asked a friend how he dealt with the hull/keel joint on his iron keel Beneteau. He told me to use Sita-flex. (Polyurethane) I did. Well, the keel was also our lightning ground and the Sitka-flex worked too good. Since the keel work, at the Panama border, in route to the Canal, only one lightning bolt hit. Yup, right on our mast. Blew up almost everything, including about 300 holes in the keel coating. The bolt hit a new Forespar lightning ground. Months of study followed. What I learned is that lightning ground systems don't ground the lightning STRIKE, they ground the 'St. Elmo's Fire'. That is the charge in the air that is opposite of the lightning charge and attracts the strike. If your hair stands on end during a lightning storm, you're about to die. Get grounded! I repaired the keel damage and left it sealed up. I also installed a ground plate. It is hooked up to the Forespar Lightning ground directly. Haven't been hit since. Besides, now we have insurance. This is the kind of subject that will draw controversy forever. Once, in a conversation with an old grinder, he maintained that no one knew the cause of hull blisters. I mentioned a new university study that was just published that their research showed 90% of all blisters are caused by standing water inside the hull, not the water outside. And the best treatment is to keep the inside dry and even better, barrier coat the INSIDE not the outside. Well, the old grinder did a double take, looked side ways at me and said "That's wrong, nobody knows the cause of blisters". End of logic and end of conversation.
Let me tell my lightning story. (I don't make this stuff up.) When we pulled into Coasta Rica in '92, it was also the start of the rainy season. That should also read 'lightning season' For the entire summer our group of buddy boats were surrounded by lightning bolts hitting nearby. No one got hit. Then in passing, I asked a friend how he dealt with the hull/keel joint on his iron keel Beneteau. He told me to use Sita-flex. (Polyurethane) I did. Well, the keel was also our lightning ground and the Sitka-flex worked too good. Since the keel work, at the Panama border, in route to the Canal, only one lightning bolt hit. Yup, right on our mast. Blew up almost everything, including about 300 holes in the keel coating. The bolt hit a new Forespar lightning ground. Months of study followed. What I learned is that lightning ground systems don't ground the lightning STRIKE, they ground the 'St. Elmo's Fire'. That is the charge in the air that is opposite of the lightning charge and attracts the strike. If your hair stands on end during a lightning storm, you're about to die. Get grounded! I repaired the keel damage and left it sealed up. I also installed a ground plate. It is hooked up to the Forespar Lightning ground directly. Haven't been hit since. Besides, now we have insurance. This is the kind of subject that will draw controversy forever. Once, in a conversation with an old grinder, he maintained that no one knew the cause of hull blisters. I mentioned a new university study that was just published that their research showed 90% of all blisters are caused by standing water inside the hull, not the water outside. And the best treatment is to keep the inside dry and even better, barrier coat the INSIDE not the outside. Well, the old grinder did a double take, looked side ways at me and said "That's wrong, nobody knows the cause of blisters". End of logic and end of conversation.
Lightning
There's no protection for your boat in a lightning strom if it is to be struck. However, being on your boat is the safest place you can be if your not handling metal. The mast of any sailboat is covered by something known as a Farady Cage. It is an inverted cone that is formed at the top of the mast and protects everything within it from a direct strike. That means if you are on deck and your mast is struck and you are not touching the rigging, you are safe from the strike.
There's no protection for your boat in a lightning strom if it is to be struck. However, being on your boat is the safest place you can be if your not handling metal. The mast of any sailboat is covered by something known as a Farady Cage. It is an inverted cone that is formed at the top of the mast and protects everything within it from a direct strike. That means if you are on deck and your mast is struck and you are not touching the rigging, you are safe from the strike.
Alan, thats not 100% true
yes, you have a much better chance on a sailboat than in in open motorboat. But it would be a mistake to think you are 100% safe, sideflashes can and do happen. With our without you touching metat. Especially if your mast is not properly grounded (e.g. deckstepped or keel stepped with no good contact to keel). You cannot prevent lightning strikes, but you can mitigate problems by having things properly bonded. Go to the link below . Its one of the most comprehensive single sites on this issue
yes, you have a much better chance on a sailboat than in in open motorboat. But it would be a mistake to think you are 100% safe, sideflashes can and do happen. With our without you touching metat. Especially if your mast is not properly grounded (e.g. deckstepped or keel stepped with no good contact to keel). You cannot prevent lightning strikes, but you can mitigate problems by having things properly bonded. Go to the link below . Its one of the most comprehensive single sites on this issue
Mis-information
abounds on the subject of lightning. I know of no subject that seems to generate more ill-informed opinion and advice. Do your own research. See the excellent link provided by Fred Ficarra. This will be a good starting point to your independant research. Regards, Gord
abounds on the subject of lightning. I know of no subject that seems to generate more ill-informed opinion and advice. Do your own research. See the excellent link provided by Fred Ficarra. This will be a good starting point to your independant research. Regards, Gord
As for your question...
A British company makes a $600 metal clasp that goes around the base of the mast and deflects the strike into two heavy wires that are cast into the water as the storm approaches. If you'd like I can look it up and get back to you. Let me know. bodonovan@vagazette.com
A British company makes a $600 metal clasp that goes around the base of the mast and deflects the strike into two heavy wires that are cast into the water as the storm approaches. If you'd like I can look it up and get back to you. Let me know. bodonovan@vagazette.com
Battery Cables
I keep an old set of battery cables on the boat. I removed the clamps from one end and stripped the insulation off of the cables for about 6 feet. When I feel like there is a danger of lightning, I clamp the battery cables to my shrouds and dropp the stripped end into the water. It won't prevent lightning, but it might channel the current away from the people in the boat.
I keep an old set of battery cables on the boat. I removed the clamps from one end and stripped the insulation off of the cables for about 6 feet. When I feel like there is a danger of lightning, I clamp the battery cables to my shrouds and dropp the stripped end into the water. It won't prevent lightning, but it might channel the current away from the people in the boat.
Jumper Cables'''
I am at a different computer and server, so I could not edit the previous posting "Battery Cables". Should have said Jumper Cables.
I am at a different computer and server, so I could not edit the previous posting "Battery Cables". Should have said Jumper Cables.
Dead people know lightnig facts
Only they really know and they ain't talking!! In the 30 years I've been in the boat building bussiness I've heard everthing theory you can imagine. It is unfortunate people are inclined to follow theories from the "dock talk" of the uninformed or uneducated as is displayed in the replies to this subject. Is the first response answer to this (Paul McGhee) willing to test his theory? I will put my confidence in the link on Tom S reply any day. The question ,do you trust "dock talk" or a study based on millions of dollars research by educated scientest ? I'll take the research any day. Have you heard of anyone getting struck by lightning at Disney World? Orlando Florida gets some of the most intense electrical storms in the world. They have lightning protection as the reaserch has concluded. You are not trying to attract lightning ,but to disapate the charge building around you via the air terminals. However ,in the event you do recieve a strike , you want it to go directly to the water outside of your boat. A conductor attached to the mast to go overboard makes a lot of sense due to the fact the aluminum is 10 times more conductive than stainless steel rigging. Also factor in the connections of tangs,pins,toggles,& turnbuckles they add even more resistance. I have seen the results of rigging dependent bonding and some of the results are devastating/spectacular. Turnbuckles welded , thru hulls blown out, propellers crystalized,dyna plates disappear. In addition to the site link from Tom S you can look at WWW.strikeshield.com. These sites afford a wealth of infomation to those willing to take the time to be educated. After being educated on this subject you will cring at the thought of the potential damage of "DOCK TALK" when this subject comes up. Nuff said , I'm finished
Only they really know and they ain't talking!! In the 30 years I've been in the boat building bussiness I've heard everthing theory you can imagine. It is unfortunate people are inclined to follow theories from the "dock talk" of the uninformed or uneducated as is displayed in the replies to this subject. Is the first response answer to this (Paul McGhee) willing to test his theory? I will put my confidence in the link on Tom S reply any day. The question ,do you trust "dock talk" or a study based on millions of dollars research by educated scientest ? I'll take the research any day. Have you heard of anyone getting struck by lightning at Disney World? Orlando Florida gets some of the most intense electrical storms in the world. They have lightning protection as the reaserch has concluded. You are not trying to attract lightning ,but to disapate the charge building around you via the air terminals. However ,in the event you do recieve a strike , you want it to go directly to the water outside of your boat. A conductor attached to the mast to go overboard makes a lot of sense due to the fact the aluminum is 10 times more conductive than stainless steel rigging. Also factor in the connections of tangs,pins,toggles,& turnbuckles they add even more resistance. I have seen the results of rigging dependent bonding and some of the results are devastating/spectacular. Turnbuckles welded , thru hulls blown out, propellers crystalized,dyna plates disappear. In addition to the site link from Tom S you can look at WWW.strikeshield.com. These sites afford a wealth of infomation to those willing to take the time to be educated. After being educated on this subject you will cring at the thought of the potential damage of "DOCK TALK" when this subject comes up. Nuff said , I'm finished
Steve: Google the usenet groups!
If you have trouble finding enough archived info here just use the Google search engine and type: "lightning group:rec.boats.cruising" to get over 1500 references for the rec.boats.cruising group alone. If you follow Phil's good advice and also type "lightening" you get another 400+ hits. In other words, nearly 2,000 articles there alone. Then you can of course try all the other serious boating groups on usenet and you will soon have more to read than you can digest in a lifetime. Having been struck twice by lightning on board "Windtryst", a Hunter 31.5 in Havre de Grace during the summer of 1991, I have since then followed countless discussions over lightning protection on boats over the past 13 years or so. Can't say I have gotten much wiser alas. For nearly any theory and/or advice there will be another one contradicting it. Often both sides have similar qualifications and credibility to offer. The reason is not hard to understand, I believe. Just try to list all the factors, on and around the vessel, that might influence the probability of a vessel being struck at sea and -- once being struck -- may influence the course that the discharge takes through the vessel. Now try to design a test matrix for a systematic laboratory experiment that addresses all these factors..... Right, you would end up with a stupendously large and costly test matrix. So, from universal principles of empirical test design alone it is safe to predict that there will not be adequate test data available on this subject and that most people who pretend to have the answers are either making enormous extrapolations from vaguely related test data or are simply hypothesizing based on personal intuition and feelings. Have fun! Flying Dutchman
If you have trouble finding enough archived info here just use the Google search engine and type: "lightning group:rec.boats.cruising" to get over 1500 references for the rec.boats.cruising group alone. If you follow Phil's good advice and also type "lightening" you get another 400+ hits. In other words, nearly 2,000 articles there alone. Then you can of course try all the other serious boating groups on usenet and you will soon have more to read than you can digest in a lifetime. Having been struck twice by lightning on board "Windtryst", a Hunter 31.5 in Havre de Grace during the summer of 1991, I have since then followed countless discussions over lightning protection on boats over the past 13 years or so. Can't say I have gotten much wiser alas. For nearly any theory and/or advice there will be another one contradicting it. Often both sides have similar qualifications and credibility to offer. The reason is not hard to understand, I believe. Just try to list all the factors, on and around the vessel, that might influence the probability of a vessel being struck at sea and -- once being struck -- may influence the course that the discharge takes through the vessel. Now try to design a test matrix for a systematic laboratory experiment that addresses all these factors..... Right, you would end up with a stupendously large and costly test matrix. So, from universal principles of empirical test design alone it is safe to predict that there will not be adequate test data available on this subject and that most people who pretend to have the answers are either making enormous extrapolations from vaguely related test data or are simply hypothesizing based on personal intuition and feelings. Have fun! Flying Dutchman
One other note --
Lighting will do whatever it damn well pleases. (you can quote me on that). Its funny when you think you are the most vulnerable, you don't get hit. And I know boats that have all sorts of dissapators, etc And were surrounded by masts and buildings all much taller than him but he got hit anyway. Go figure. I'll relate another story I was trapped on LI Sound this summer (Monday July 21st) and I couldn't outrun a storm (I was trying desperately to make it into Pt Jeff before it hit). I had to turn and face the storm. The winds and lightning were incredible. It was a virtual white out, the admiral was just about crying, the thunder all around was deafening at times. I told her to sit on the wooden companionway stairs and keep her hands in. I was steering the boat via an autopilot remote away from the helm and the split backstays (thank god for that little gadget). Just when one storm cell made it through another one followed with more lightning, when I thought I was in the clear and through the last cell, a lone lightning strike hit 50, 75, 100? yards away (how can you really gauge these things?) All I remember was the flash was at the same moment as the thunder. I didn't even have time to react. After that one moment I kept thinking "Why in heck didn't that bolt of lightning hit me? I'm the tallest thing out here by 50 feet for miles ?!?" And then it dawned on me "Lighting will do whatever it damn well pleases." BUT I will say that if it does hit your boat I am "Very Confident" that a well grounded boat will mitigate and reduce problems more than one that isn't. But if its a "mega strike" all bets are off and you just found yourself being very unlucky. But one consolation is that it is rare to have fatalities from sailboat lightning strikes and its more common to see fatalities from other causes...in other words "don't sweat it" As a post script, when I went back to my radar chartplotter, I noticed I had lost my Radar portion and as the next few days went by I had come to find out the EMP from the close by lightning strike also blew out my Accuguage tank monitors, an "Echo Charger".......and a pair of underwear ;-)
Lighting will do whatever it damn well pleases. (you can quote me on that). Its funny when you think you are the most vulnerable, you don't get hit. And I know boats that have all sorts of dissapators, etc And were surrounded by masts and buildings all much taller than him but he got hit anyway. Go figure. I'll relate another story I was trapped on LI Sound this summer (Monday July 21st) and I couldn't outrun a storm (I was trying desperately to make it into Pt Jeff before it hit). I had to turn and face the storm. The winds and lightning were incredible. It was a virtual white out, the admiral was just about crying, the thunder all around was deafening at times. I told her to sit on the wooden companionway stairs and keep her hands in. I was steering the boat via an autopilot remote away from the helm and the split backstays (thank god for that little gadget). Just when one storm cell made it through another one followed with more lightning, when I thought I was in the clear and through the last cell, a lone lightning strike hit 50, 75, 100? yards away (how can you really gauge these things?) All I remember was the flash was at the same moment as the thunder. I didn't even have time to react. After that one moment I kept thinking "Why in heck didn't that bolt of lightning hit me? I'm the tallest thing out here by 50 feet for miles ?!?" And then it dawned on me "Lighting will do whatever it damn well pleases." BUT I will say that if it does hit your boat I am "Very Confident" that a well grounded boat will mitigate and reduce problems more than one that isn't. But if its a "mega strike" all bets are off and you just found yourself being very unlucky. But one consolation is that it is rare to have fatalities from sailboat lightning strikes and its more common to see fatalities from other causes...in other words "don't sweat it" As a post script, when I went back to my radar chartplotter, I noticed I had lost my Radar portion and as the next few days went by I had come to find out the EMP from the close by lightning strike also blew out my Accuguage tank monitors, an "Echo Charger".......and a pair of underwear ;-)
Strikeshield
That Strikeshield lightning protection system looks like a great solution for boats which weren't designed/built with lightning grounding. It accomplishes what people are trying to do with jumper cables. Jumper cables won't hurt, but they also won't provide a substantial enough path for the lightning to use. Remember, lightning wants to come down the aluminum mast, not the stainless shrouds. The one weakness I see in the Strikeshield is that you are forcing the electricity to make a hard turn from going down the mast to the ground wires in the system. A standard practice when wiring lightning grounds for communications towers is to always make gentle bends. http://www.strikeshield.com/ Ron Mehringer H26 Hydro-Therapy
That Strikeshield lightning protection system looks like a great solution for boats which weren't designed/built with lightning grounding. It accomplishes what people are trying to do with jumper cables. Jumper cables won't hurt, but they also won't provide a substantial enough path for the lightning to use. Remember, lightning wants to come down the aluminum mast, not the stainless shrouds. The one weakness I see in the Strikeshield is that you are forcing the electricity to make a hard turn from going down the mast to the ground wires in the system. A standard practice when wiring lightning grounds for communications towers is to always make gentle bends. http://www.strikeshield.com/ Ron Mehringer H26 Hydro-Therapy
Lightening Likes Gentle Bends
Listen to what Ron has to say - Lightening likes gentle bends. The US Forest Service design requirements for fire lookout cabs (those little buildings on the top of mountain peaks) is for solid copper wire down each roof ridge and corner of the cab and thence to the ground via a deeply driven ground rod. The bends are gradual - never sharp. The electrical current needs a path akin to a freeway on/off-ramp (turnpikes to easterners!) when making a change in direction. As a sidebar, the fire lookouts stay in their cabs protected by the wiring on the outside. They still have to work with the map and direction finder even during the course of an electrical storm and call in the township, range, section number (for western forests) of the "smokes". Fire lookouts work for a very small pay and many of them have been phased out due to sophisticated electronics and budget cuts. Most of the cabs were built back in the '30s and '40s to a "standard plan". Visitors were always welcomed to these remote locations by the lookout and greeted to a knockout view due to their locations which were on the tallest mountain peaks around.
Listen to what Ron has to say - Lightening likes gentle bends. The US Forest Service design requirements for fire lookout cabs (those little buildings on the top of mountain peaks) is for solid copper wire down each roof ridge and corner of the cab and thence to the ground via a deeply driven ground rod. The bends are gradual - never sharp. The electrical current needs a path akin to a freeway on/off-ramp (turnpikes to easterners!) when making a change in direction. As a sidebar, the fire lookouts stay in their cabs protected by the wiring on the outside. They still have to work with the map and direction finder even during the course of an electrical storm and call in the township, range, section number (for western forests) of the "smokes". Fire lookouts work for a very small pay and many of them have been phased out due to sophisticated electronics and budget cuts. Most of the cabs were built back in the '30s and '40s to a "standard plan". Visitors were always welcomed to these remote locations by the lookout and greeted to a knockout view due to their locations which were on the tallest mountain peaks around.
LIghtning Protection???
A month or two ago there was a thread on trailersailor.com on lightning. The instigator of this thread was a science teacher who had an intense interest in lightning. I wrote a response to his thread in which I said I used the jumper cables. I defended my position by stating that, not only would the jumper cables help lead the discharge to the water, but it would also help dissipate the charge so that it might prevent a lightning strike. He basically debunked my statement that it would help prevent a lightning discharge. I disagree with him, but he did appear to have a very detailed knowledge. He did believe the jumper cables would help, but he suggested adding a six foot grounding rod to the end of the cables. I don't know that his modification is an improvement, but it would not hurt anything. I still believe my idea of using the jumper cables is a good idea. The jumper cables are not my original idea. My sailing instructor, Ted Enlund of Panama City, suggested this idea. I don't believe the lighning will neccessarily come down the mast as opposed to the shrouds. I looked at a Mac 25 which had been struck by lightning. It appearred that the path it took was down the shrouds to the chain plates and then blew a hole in the hull at the water line below the chain plates. The lighning will pick the path of least resistance, which should be down the shrouds and jumper cables to the water. It will not neccessarily pick the path down the mast, because it does not have a full conductive path to the water. Connecting the jumper paths to the mast would be a good idea. I did a lot of hedging in the above. As someone said "lightning will do what it wants". All you can do is help a little bit.
A month or two ago there was a thread on trailersailor.com on lightning. The instigator of this thread was a science teacher who had an intense interest in lightning. I wrote a response to his thread in which I said I used the jumper cables. I defended my position by stating that, not only would the jumper cables help lead the discharge to the water, but it would also help dissipate the charge so that it might prevent a lightning strike. He basically debunked my statement that it would help prevent a lightning discharge. I disagree with him, but he did appear to have a very detailed knowledge. He did believe the jumper cables would help, but he suggested adding a six foot grounding rod to the end of the cables. I don't know that his modification is an improvement, but it would not hurt anything. I still believe my idea of using the jumper cables is a good idea. The jumper cables are not my original idea. My sailing instructor, Ted Enlund of Panama City, suggested this idea. I don't believe the lighning will neccessarily come down the mast as opposed to the shrouds. I looked at a Mac 25 which had been struck by lightning. It appearred that the path it took was down the shrouds to the chain plates and then blew a hole in the hull at the water line below the chain plates. The lighning will pick the path of least resistance, which should be down the shrouds and jumper cables to the water. It will not neccessarily pick the path down the mast, because it does not have a full conductive path to the water. Connecting the jumper paths to the mast would be a good idea. I did a lot of hedging in the above. As someone said "lightning will do what it wants". All you can do is help a little bit.
Capacitance thoughts
Like Tom, I was making an open water passage between Michigan's lower and Upper Peninsula when a strike hit so close as to appear that the sound and flash were simultaneous. The shock wave of the sound was felt in the hull. Doing the math... for the sound and light to be identical... means that it had to be close. Unlike Tom's nearby strike, this strike was the only one in the area for many miles. We had heard distant thunder about an hour earlier but it had ended. We heard no other strikes in the time after the one which was so close. I and my crew were hunkered down below under autopilot. Both my brother in law and I confirmed the flash and the sound were simultaneous. His son was napping and when he woke later, we asked if he'd felt the strike... as he is deaf... he had not. We suffered no damage. I'm a big advocate of logical thought. Lightening seems to be a tough one however to pin down ... because as Tom says, "It seems to do as it pleases." The question, is there any thing in particular that pleases it? Much logic is based on the question, Why? and the resulting answers that fit only and explanation of the circumstances. In Tom's case and more especially in mine where the single strike was the only one in perhaps 10 miles... why had it hit so close to the boat but yet not hit it? One possible answer is that it doesn't hit the tallest nearby object... something all of us have heard. Does it that rather seek the shortest path to ground? Lightning is caused by an electrical charged cloud that in very many ways resembles an electrical capacitor. Capacitors are governed by common electrical disciplines of thought. Two opposing charges are held at bay by an insulator having an adequate dielectric value. The amount of capacitance is dictated by the size of the plates and the kind and spacing of dielectric insulation between the plates. If the insulator breaks down or its dielectric value becomes less than the laws of physics allow to keep the two potentials at bay, the charge will dissipate to the opposite polarity to obtain neutral electrical potential. Two scenarios can happen. The charge may increase beyond a given dielectric resistance ability or the dielectric's value lessons for some reason. What happens if a cloud rolls across the surface of the water with almost enough potential to break down the air insulator and comes upon a sailboat with a 30 foot mast which is not grounded... does the air dielectric between cloud and ground change? No. As the cloud passes that boat to another with a 30 foot mast which is grounded, does the air dielectric change? Yes, by a reduction of 30 feet worth of air. Also, dielectrics are based on their relationship to air, it having a number value of 1.0. Polystyrene has a value of 2.6 or nearly three times the resistance of air. Roughly, this means that if a boat has six feet of height and is made of fiberglass, it has an equivalence of 15.6 feet longer distance for a lightening path than the surrounding water. And this takes no account that the dielectric value of air greatly humidified in a thunderstorm may be far less than the value of 1.0 If arbitrarily we suggested the value dropped to 1/3 its normal value during a heavy rain squall which sounds reasonable to me... then the dielectric difference between the boat and the surrounding surface would be the equivalent of a 46.8 feet shorter path for the lightning to strike beside the boat rather than on it. If lightening is seeking not the tallest object but rather the shortest path to ground... then that is beside the boat... not through it if the boat is ungrounded. Grounding the mast however, raises the ground above your boat by the length of the mast. So, grounding a boat shortens the path to ground making the boat the most favorable path... ungrounded, the nearby water surface is the favorable path. I think I'll stay ungrounded... it at least worked for me once.
Like Tom, I was making an open water passage between Michigan's lower and Upper Peninsula when a strike hit so close as to appear that the sound and flash were simultaneous. The shock wave of the sound was felt in the hull. Doing the math... for the sound and light to be identical... means that it had to be close. Unlike Tom's nearby strike, this strike was the only one in the area for many miles. We had heard distant thunder about an hour earlier but it had ended. We heard no other strikes in the time after the one which was so close. I and my crew were hunkered down below under autopilot. Both my brother in law and I confirmed the flash and the sound were simultaneous. His son was napping and when he woke later, we asked if he'd felt the strike... as he is deaf... he had not. We suffered no damage. I'm a big advocate of logical thought. Lightening seems to be a tough one however to pin down ... because as Tom says, "It seems to do as it pleases." The question, is there any thing in particular that pleases it? Much logic is based on the question, Why? and the resulting answers that fit only and explanation of the circumstances. In Tom's case and more especially in mine where the single strike was the only one in perhaps 10 miles... why had it hit so close to the boat but yet not hit it? One possible answer is that it doesn't hit the tallest nearby object... something all of us have heard. Does it that rather seek the shortest path to ground? Lightning is caused by an electrical charged cloud that in very many ways resembles an electrical capacitor. Capacitors are governed by common electrical disciplines of thought. Two opposing charges are held at bay by an insulator having an adequate dielectric value. The amount of capacitance is dictated by the size of the plates and the kind and spacing of dielectric insulation between the plates. If the insulator breaks down or its dielectric value becomes less than the laws of physics allow to keep the two potentials at bay, the charge will dissipate to the opposite polarity to obtain neutral electrical potential. Two scenarios can happen. The charge may increase beyond a given dielectric resistance ability or the dielectric's value lessons for some reason. What happens if a cloud rolls across the surface of the water with almost enough potential to break down the air insulator and comes upon a sailboat with a 30 foot mast which is not grounded... does the air dielectric between cloud and ground change? No. As the cloud passes that boat to another with a 30 foot mast which is grounded, does the air dielectric change? Yes, by a reduction of 30 feet worth of air. Also, dielectrics are based on their relationship to air, it having a number value of 1.0. Polystyrene has a value of 2.6 or nearly three times the resistance of air. Roughly, this means that if a boat has six feet of height and is made of fiberglass, it has an equivalence of 15.6 feet longer distance for a lightening path than the surrounding water. And this takes no account that the dielectric value of air greatly humidified in a thunderstorm may be far less than the value of 1.0 If arbitrarily we suggested the value dropped to 1/3 its normal value during a heavy rain squall which sounds reasonable to me... then the dielectric difference between the boat and the surrounding surface would be the equivalent of a 46.8 feet shorter path for the lightning to strike beside the boat rather than on it. If lightening is seeking not the tallest object but rather the shortest path to ground... then that is beside the boat... not through it if the boat is ungrounded. Grounding the mast however, raises the ground above your boat by the length of the mast. So, grounding a boat shortens the path to ground making the boat the most favorable path... ungrounded, the nearby water surface is the favorable path. I think I'll stay ungrounded... it at least worked for me once.
Arlyn, Everything in your post makes sense
And I can't argue with it. (I have a EE degree). I have thought long and hard on this subject. BUT if you are the unlucky guy that "does" get a direct strike from lightning and you don't have the mast/shrouds grounded, then when the lightning comes down its going to look for a path out. And without a good path its going to "blow through" things to find ground & most likely it gonna blow holes through the fiberglass (relax everyone - pin hole sized ones normally) and maybe transversing a human or two in the process. But luckily we know through data that is very rare. One side note to help , I have a keel stepped mast on my C36, but it is not electrically bonded to the hull. (Though with the rain and water that day I don't doubt I might have had some conductivity from the mast base to the keel bolts....I don't have a dry bilge) I was going to bolt a 4 guage wire from the mast to the keel bolt this past winter, but I never got around to it. Did not having my mast "totally" bonded prevent me from getting that lightning strike? I can't say -- I really don't know and I think it would be a mistake for anyone to try and come to that conclusion. I have searched and analyzed data and from what I see bonded or not bonded boats seem to get struck with the same frequency. I understand the research and what the professors say. But my "heart" agree's with Arlyn. I might be wrong, but I think the IDEAL setup would be an isolated mast such as Arlyn suggest's BUT one that will channel lightning down through my keel if I get unlucky and a strike does hit me. Arlyn, do you know of any type of device that I could put in-line with my keel bolt connection that is non-conductive, but if there is a high voltage/High frequency strike would easily conduct the lightning strike. That would be my ideal set-up...
And I can't argue with it. (I have a EE degree). I have thought long and hard on this subject. BUT if you are the unlucky guy that "does" get a direct strike from lightning and you don't have the mast/shrouds grounded, then when the lightning comes down its going to look for a path out. And without a good path its going to "blow through" things to find ground & most likely it gonna blow holes through the fiberglass (relax everyone - pin hole sized ones normally) and maybe transversing a human or two in the process. But luckily we know through data that is very rare. One side note to help , I have a keel stepped mast on my C36, but it is not electrically bonded to the hull. (Though with the rain and water that day I don't doubt I might have had some conductivity from the mast base to the keel bolts....I don't have a dry bilge) I was going to bolt a 4 guage wire from the mast to the keel bolt this past winter, but I never got around to it. Did not having my mast "totally" bonded prevent me from getting that lightning strike? I can't say -- I really don't know and I think it would be a mistake for anyone to try and come to that conclusion. I have searched and analyzed data and from what I see bonded or not bonded boats seem to get struck with the same frequency. I understand the research and what the professors say. But my "heart" agree's with Arlyn. I might be wrong, but I think the IDEAL setup would be an isolated mast such as Arlyn suggest's BUT one that will channel lightning down through my keel if I get unlucky and a strike does hit me. Arlyn, do you know of any type of device that I could put in-line with my keel bolt connection that is non-conductive, but if there is a high voltage/High frequency strike would easily conduct the lightning strike. That would be my ideal set-up...
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