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Lightning Protection questions
On Nov 12, 7:57*pm, Jere Lull wrote:
My evidence is anecdotal only, primary one was one boat getting a bottle brush installed by the factory team. Lightning rods don't attract lightning. Lightnng will strike because electrical charges must be connected from the cloud to ground. Something will attract or will prevent lightning is often myth because many know only from observation rahter than first learn the basic technology. Observation without fundamental knonwledge is also called junk science reasoning. Required is little to connect ligthning harmlessly to earth. Ben Franklin demonstrated the concept in 1752 to halt damage to churches. The term 'little' is subjective. But if one does not first learn the basics, then 'little' becomes 'massive'. A U of FL article cited by Roger Long provides fundamental information. Lightning may even strike a valley rather than nearby hills. Why? Where are those charges that lightning must connect to? Using only observation, then clearly lightning seeks the lowest point. First learn the science to understand why lightning strikes a valley or a nearby mountain, or why the best place to strike was that one boat. The anecdotal evidence is flawed because its conclusoin is based on an observation without comprehensive study of what connected to that boat, the content of soil beneath that boat, where the boat was located in relation to earthed charges, etc. |
Lightning Protection questions
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Lightning Protection questions
Wayne.B wrote:
On Wed, 12 Nov 2008 17:20:21 -0800 (PST), wrote: The anecdotal evidence is flawed because its conclusoin is based on an observation without comprehensive study of what connected to that boat, the content of soil beneath that boat, where the boat was located in relation to earthed charges, etc. OK, let me ask you this: 300 miles offshore in more than 5,000 feet of salt water, lightning decides to strike a nearby wave top instead of the well grounded 80 ft mast of an all aluminum boat. Why? Butterflies Wings or in this case, probably dust particles or rain drops. The initial ionisation of the air immediatly below the leader of the stroke is dependent on field strength but field strength in most stuations falls off with the square of the distance so a rain drop of lets say 3 mm diameter a meter from the tip of the leader has more influence than that mast 100 metres away. Its only if you have sharp enough edges and enough field strength to get local ionisation on the rigging, St Elmo's fire being the extreme example, that the difference between an 80 ft mast and a 8 ft wave becomes significant. Waves dont have sharp edges . . . -- Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED) ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk [at]=@, [dash]=- & [dot]=. *Warning* HTML & 32K emails -- NUL: 'Stingo' Albacore #1554 - 15' Early 60's, Uffa Fox designed, All varnished hot moulded wooden racing dinghy. |
Lightning Protection questions
"Jere Lull" wrote in message news:2008111219570616807-jerelull@maccom... On 2008-11-12 05:25:05 -0500, "Roger Long" said: Jere Lull wrote: But there are funner things to do since it seems the commercial products seem to attract strikes. I don't see a shred of evidence to support this. I think it more likely that people who are on the water enough in frequent strike zones to be at high risk install protection and therefore get struck more often simply because they are at higher risk. My evidence is anecdotal only, primary one was one boat getting a bottle brush installed by the factory team. Though the boat's mast was relatively short compared to dozens of boats around it, it was the only one hit -- a couple of weeks later. The device's insurance ensured they paid nothing to get everything fixed, but they weren't able to get enough of the systems up to use the boat that season. Even land-based lightning rods have to be very carefully installed or they attract strikes. (that's something I read in school, perhaps connected to Ben Franklin.) This is the first time anyone has mentioned the 'bottle brush' but I have always believed that a spiky device at the very top of the lightning rod is essntial if it is to act effectively to reduce the possibility of a dangerous strike. My understanding is that in the moments before a strike the 'positive' charge in the clouds draws up a negative charge through the lightning rod. This, in itself, increases the likelihood of a strike onto the mast, but if you have sharp points at the top of the lightning rod these concentrate the local negative charge so much that the positive force in the cloud is dissipated to earth down your lightning rod before it can build to a high enough potential in the local clouds to break through the atmosphere as a full lightning strike. If I am right on this, and I would welcome anyone who can comment on this theory, then there are two ways to go, either have a proper lightning rod with sharp spikes on it, or do not have an earthed lightning rod at all. In a previous post I told how I was caught out in open water during a lightning storm and yet my metal mast, which was not earthed, was not struck even though strikes were going into the sea all around me. |
Lightning Protection questions
I saw something in some science news on the net shortly before I started
getting interested in this subject, I'll have to find it again but the gist from a quick skim was that some scientists now believe that ground strikes are following an ionization channel opened up one of the high energy cosmic rays that are constantly bombarding the earth. The strike may divert to a high object near the ground but the ray path could also lead it to the water or a lower object. -- Roger Long |
Lightning Protection questions
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Lightning Protection questions
On Thu, 13 Nov 2008 05:25:43 -0500, "Roger Long"
wrote: I saw something in some science news on the net shortly before I started getting interested in this subject, I'll have to find it again but the gist from a quick skim was that some scientists now believe that ground strikes are following an ionization channel opened up one of the high energy cosmic rays that are constantly bombarding the earth. The strike may divert to a high object near the ground but the ray path could also lead it to the water or a lower object. Great. Now it's all very clear. --Vic |
Lightning Protection questions
On 2008-11-13 03:40:42 -0500, "Edgar" said:
This is the first time anyone has mentioned the 'bottle brush' but I have always believed that a spiky device at the very top of the lightning rod is essntial if it is to act effectively to reduce the possibility of a dangerous strike. That is one theory, the use of a "bottle brush" conductor is another; there are others. Knowing a bit about electrical engineering, electricity and electronics, I can follow the observations and math and find good points in many of the theories advanced. The problem is that no matter how long scientists (and snake-oil salesmen) have been studying the problem, lightning strikes are relatively random (determined by cosmic rays?) with the probability of a strike in a particular location only slightly affected by man-made agents. There *are* well-documented things to do (or not) before you get hit: Do not ground to your through hulls, ground to something big, preferably without vulnerable hull between, try to "persuade" the lightning to stay outside of the boat's interior, put sensitive electronics in a Faraday cage, add bonding to fixed equipment separate from grounding.... Personally, the best way to avoid lightning is to be elsewhere. Given unlimited money, we'd have a metal hull. Given reality, my efforts go first to damage-control, then relaxing about those things I can't control. -- Jere Lull Xan-à-Deux -- Tanzer 28 #4 out of Tolchester, MD Xan's pages: http://web.mac.com/jerelull/iWeb/Xan/ Our BVI trips & tips: http://homepage.mac.com/jerelull/BVI/ |
Lightning Protection questions
In article , Vic Smith wrote:
On Thu, 13 Nov 2008 05:25:43 -0500, "Roger Long" wrote: I saw something in some science news on the net shortly before I started getting interested in this subject, I'll have to find it again but the gist from a quick skim was that some scientists now believe that ground strikes are following an ionization channel opened up one of the high energy cosmic rays that are constantly bombarding the earth. The strike may divert to a high object near the ground but the ray path could also lead it to the water or a lower object. Great. Now it's all very clear. VBG Oh yes, that made me laugh. TY. Justin. -- Justin C, by the sea. |
Lightning Protection questions
On Thu, 13 Nov 2008 18:11:35 GMT, Jere Lull wrote:
Given unlimited money, we'd have a metal hull. Somewhere around sixty or seventy feet and up, everything seems to be steel and aluminum. My 22 foot fishboat is metal. It cost me two grand. Casady |
Lightning Protection questions
Jeeezeus H Christ............what a thread!
This makes my worrying about a little rust seem like nuthin. The more I learn about plastic boats the more I like steel. |
Lightning Protection questions
Jere Lull wrote:
On 2008-11-13 03:40:42 -0500, "Edgar" said: This is the first time anyone has mentioned the 'bottle brush' but I have always believed that a spiky device at the very top of the lightning rod is essntial if it is to act effectively to reduce the possibility of a dangerous strike. That is one theory, the use of a "bottle brush" conductor is another; there are others. Knowing a bit about electrical engineering, electricity and electronics, I can follow the observations and math and find good points in many of the theories advanced. The problem is that no matter how long scientists (and snake-oil salesmen) have been studying the problem, lightning strikes are relatively random (determined by cosmic rays?) with the probability of a strike in a particular location only slightly affected by man-made agents. Well, there is the exception of the folks at U of Fl. who launch rockets trailing thin wires into thunder clouds........ Other than that, fair enough.. Cheers Martin |
Lightning Protection questions
On Nov 13, 5:25*am, "Roger Long" wrote:
... but the gist from a quick skim was that some scientists now believe that ground strikes are following *an ionization channel opened up one of the high energy cosmic rays that are constantly bombarding the earth. *The strike may divert to a high object near the ground but the ray path could also lead it to the water or a lower object. Which says nothing useful. Cosmic ray does not construct a staight conductive path through the air. Obviously lightning snakes in various directions to earth; does not follow the straight path of a cosmic ray. A microscopic path of ionied air might cause lightning to snake slightly left rather than right. It is still constructing a plasma path from cloud to earth because it must connect charges in clouds (+ or 1) to charges on earth (- or+). If a conductive path uses a boat, then a massive current later will follow that path through the boat. Nothing will 'avoid' that strike. Another myth promotes pointy items. Demonstrated in experiment is that better protection uses blunt rather than pointy rods. Still when lightning strikes, then either it does significant damage OR is conducted harmlessly to beneath the boat. As the U of FL article demonstrates, lightning can be conducted harmlessly if basic guidelines are followed. |
Lightning Protection questions
On Thu, 13 Nov 2008 20:34:47 -0000, Justin C
wrote: In article , Vic Smith wrote: On Thu, 13 Nov 2008 05:25:43 -0500, "Roger Long" wrote: I saw something in some science news on the net shortly before I started getting interested in this subject, I'll have to find it again but the gist from a quick skim was that some scientists now believe that ground strikes are following an ionization channel opened up one of the high energy cosmic rays that are constantly bombarding the earth. The strike may divert to a high object near the ground but the ray path could also lead it to the water or a lower object. You don't get one track, you get an acre of them from just one energetic cosmic ray. Within that two hundred feet, you would be shaking the dice. Casady |
Lightning Protection questions
On Thu, 13 Nov 2008 22:51:09 -0500, Marty wrote:
Jere Lull wrote: .... no matter how long scientists (and snake-oil salesmen) have been studying the problem, lightning strikes are relatively random (determined by cosmic rays?) with the probability of a strike in a particular location only slightly affected by man-made agents. Well, there is the exception of the folks at U of Fl. who launch rockets trailing thin wires into thunder clouds........ Other than that, fair enough.. Cheers Martin Gotta be kidding. The statistics for tall buildings show a routine series of strikes every year... Brian W |
Lightning Protection questions
Wayne.B wrote:
On Sat, 8 Nov 2008 12:40:47 -0500, "Roger Long" wrote: This winter's major project is to add some serious lightning protection to "Strider". What I have now is probably sufficient to increase the odds of being alive to climb into the dinghy and watch the boat sink but I'd prefer to sail home. It's not a subject that comes up often for a designer of metal vessels so I've been look around the web and learned: The ABYS standards of 1 sq. foot of ground area and 8 GA conductors are marginal and highly suspect. Probably nothing feasible is going to protect a plastic boat in fresh water. Although I'm generally in salt, I'd like to be ready to go up some rivers. Conductors should have a minimum 8" radius bend. I've got a metal mast support strut that has sufficient through bolts to the mast deck step to make it electrically continuous. This lands on a wide, internal ballast keel. I plan to run flat copper straps about 1/16" x 1/2" (approximate cross section of 4 ga wire) from this up each side to 6" x 24" bronze ground plates on each side of the hull. These will be about 1/16" thick and through bolted to the hull at each corner. Inside, there will be straps under the bolt heads in an "X" pattern with the strap from the mast strut lead to the center. There will also be a 4 Ga wire or strap from the engine block to one of these plates to help protect the engine bearings. Comments welcome on this conceptual plan which will also include other secondary bonding additions as recommended by ABYC. Here's my main question for someone who understands high voltage better than I do: I only have 6" under the cabin sole. How critical is the 8" bend? Can I compensate for the tighter radius by increasing the conductor cross section? How much? The turn is more than 90 degrees because the straps have to run back up the hull deadrise about two feet to where I can locate the plates and through bolts. I don't think putting the plates on the keel sides is feasible. Another question: Is the standard metal rod VHF antenna at the top of the mast with the typical metal can on a bracket riveted to the mast a sufficient air terminal or should I add a dedicated rod? I have no illusions about having any electronics working after a strike on a 32 foot boat but replacement of my minimalist outfit wouldn't break me financially. I'd just like to be alive with a working engine and watertight boat. I know of at least half a dozen sailboats that have been hit, one of them twice on the same day. Only one sank and that was because the lightning decided to exit through a plastic knot meter impeller leaving a 1 inch hole in the bottom. It could have been plugged if there had been anyone on board at the time. What you are planning sounds like overkill to me, especially for Maine. Where we live now there are thunderstorms almost everyday throughout the summer but you don't hear about that many hits on boats. Golfers seem to be the target of choice and they usually fare poorly. The reason it may be overkill is not because of the frequency of lightning hits, but instead that his boat is already properly grounded. Lightning will go through the path of least resistance, which in your case is through the mast and keel. Not sure about the configuration of your internal ballast keel, but if you are talking about completing the connection of the mast to the keel, this is a good idea. My mast is stepped on the cabin roof, so I ran a humungous copper cable from that to my keel bolts, similarly to what you contemplate doing. On Lake Michigan, I had a close lightning hit that traveled up my outboard to the tiller I was holding and it knocked me clear across the cockpit. At that point I installed my grounding cable. I would not recommend any kind of rod atop your mast, as it may attract lightning. If you are really concerned, have a backup antenna deck mounted that you could switch to, if necessary. Sherwin |
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