This is a bit of a hot button topic for me because – most of my life – I’ve been dealing with lightning in one way or another. And sometimes I get a little, well, impatient with the folklore surrounding it.
Ever since Ben Franklin invented the lightning rod (his kite experiment wasn’t intended to “discover” electricity) people have been saying: “there ain’t nothin’ folks can do to prevent lightnin’ damage.” In fact, some of the religions of the time preached that: “if it’s God’s will to smite your house with fire from the sky, it’s sinful to interfere!” Ironically, then as well as now, it’s often churches that burn to the ground most frequently from lightning strikes. If you live in the Southeast, take a good look at the roof ridge line of any nearby church. See all those lightning rods? Some are hidden, but ask the curator what that decorative-looking ball in the middle of the church’s spire is for, and (if the pastor isn’t within earshot) he’ll tell you that the ball is made of glass, and that it’s there so if the spire takes a lightning hit the ball will shatter from shock heating, and then that’s his cue to inspect the lightning arrestors and grounding system.
I was a broadcast engineer for many years in Nebraska. We had a five tower array that was on a hilltop, making it the highest object in a 60 mile radius (kinda like being a lonely sailboat out in an ocean of corn). And I’d sit there peering out the window while the towers took hit after hit – sometimes so powerful that the bolt would split into five forks and hit all the towers simultaneously. The transmitter building lit up like the inside of a giant flashbulb, and the metallic smell of ozone filled it for several minutes. Twice the 100 kilovolt-amp transformer, owned by the power company just outside, exploded with a tremendous thud, a shower of blue sparks and green copper plasma – only causing me to shrug and start the diesel generator. And while that energy would leave burn spots on the inside of the transmitter cabinets, all the tiny delicate transistors in that building didn’t suffer any damage at all. Why? In two words: Grounding and Bonding.
There were other times that I’d listen to loud snaps coming from inside the transmitter, while I watched arcs jump across the Johnnyball guywire insulators at the tower, in response to lightning strikes that I could see discharging miles away. It’s called “induced lightning” and it’s caused by the magnetic field created from several million amps being discharged vertically ground-to-sky (the principal direction of a lightning discharge). Anyone familiar with the inner workings of an air core transformer will recognize the effect. The current gets “induced” in any vertical conductive object some distance away… Like an aluminum sailboat mast. It doesn't take a direct hit to cause damage.
One of the things that people noticed after Ben started selling his rods was that buildings with them seldom seemed to use them because the buildings got hit less frequently. A lot of knowledge has been acquired since then, and we know today that a sharp pointed conductive object will dissipate the charge in the air immediately surrounding those rods, delaying or preventing the discharge from selecting exactly that location to finally breakdown the natural insulation of the air. Someone noticed quite a few years ago that barbed wire seemed to protect fence posts from lightning hits because it had lots of really pointy conductive surfaces. Later, someone invented the “brush looking thingy” that concentrated lots of sharp points in one place (http://www.lightningmaster.com/) in order to prevent a strike from occurring. And smart people started putting them at the tops of their sailboat masts.
The next time you’re on an airliner, take a window seat behind the wing and look closely at the training edge of the wing. You’ll see lots of furry looking protrusions about the diameter of a pencil sticking out of the trailing edge (see image). Those are static dischargers, and they’re there to discharge the buildup of electrical charges from playing havoc with the radios. They work on the same principal as those brush looking things people put on top of their masts. Yea, right, companies like Boeing spend umpteen dollars each to put those little suckers on their airplanes ‘cause they’re bunk ;-) You’ll see them on ALL airplanes that are certified to fly on instruments – all the way down to little Cessnas and Pipers - because the FAA requires them to be there (that’s what I was taught in school as part of becoming an instrument-rated commercial pilot). They work. And airplanes in flight don’t even have ground connections!
Technically, by the way, “lightning rods” are properly called “air terminals.” An air terminal performs two duties: 1) Prevent a lightning strike from occurring by discharging the developed difference of electrical potential of the air immediately surrounding it, thus making the area less attractive to a strike and; 2) provide a safer path to ground should a strike still occur. While the task of providing a safe path to ground is obvious and well understood - even though Ben Franklin observed the preventative action of a sharp-pointed object* - many people are still unaware of the preventative capacity of air terminals. A good path to ground isn't necessary to gain the benefits of strike prevention (bonding is still important). In fact, it's impossible in some applications to have any ground at all (like with aircraft in flight).
There is a great deal of assembled knowledge on how to protect boats from lightning in the National Fire Prevention Association (NFPA) standard number 780: http://www.nfpa.org/aboutthecodes/Ab...asp?DocNum=780. The NFPA are the same people who write the National Electrical Code, and they know a thing or two about keeping electricity from burning things up. I suggest consulting them first before factoring in all the other folklore.
So what should someone do in cases where they don’t have good lightning protection? 1) Go by the surplus store and buy some steel ammo cans. They’re cheap. Disconnect your radios completely and put them in the ammo cans when you aren’t using them. 2) If you’re caught out without ammo cans, put the radios in anything metal that completely surrounds them. If you have an oven on board, that’s a great location. If you don’t, then carry a roll of aluminum foil for just that contingency. Wrap the completely disconnected radios in foil. If you take a hit, plan on replacing the coax cables running up your mast because they will likely have conductive arc paths burned in them between the center conductor and the outer braid, lowering the breakdown voltage thereafter (that only a "megger" - not a low voltage ohm meter - will ever detect). Are your radios acting oddly after that last thunderstorm...? If you don't like the prospect of replacing all your coax, buy a coax switch that shorts your antennas and coax when they aren't in use and has arc protection for when you are using them (or forget to throw the switch at the slip): http://www.hamradio.com/detail.cfm?pid=H0-008459.
I’m currently in the San Francisco area. People don't rightly concern themselves much with lightning here. One could live an entire lifetime here without ever seeing even one of the thunderstorms that I witnessed on a weekly basis during Nebraska summers. In fact, if you really enjoy (or want to avoid) thunderstorms, there’s a map of how frequently lightning strikes occur in the United States: http://www.lightningsafety.noaa.gov/lightning_map.htm. (For real lightning aficionados, there’s no place like Central Africa.)
As for your own personal safety: averaged out over many years, do you know which single natural phenomenon's death rates ranks right up there with cold weather, tornadoes, hurricanes, floods, earthquakes, and even volcanoes? Until the weather service recently started keeping records on heat related deaths, ranking neck-and-neck as the top killer was lightning. In a fiberglass boat, it isn't practical to seal yourself inside a metal can. There are some advantages to metal-hulled boats…
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*Franklin wrote: "...upright Rods of Iron, made sharp as a Needle and gilt to prevent Rusting, and from the Foot of those Rods a Wire down the outside of the Building into the Ground;...Would not these pointed Rods probably draw the Electrical Fire silently out of a Cloud before it came nigh enough to strike, and thereby secure us from that most sudden and terrible Mischief!" Following a series of experiments on Franklin's own house, lightning rods were installed on the Academy of Philadelphia (later the University of Pennsylvania) and the Pennsylvania State House (later Independence Hall) in 1752.
lightening rod and dissipater connections to ground
pbryant sir, thanks for your splendid reply!
While waiting to see if anyone else was going to post, couple days ago, up here in Sonoma we had some tall dark cumulus move in overhead and produce some loud claps of thunder.
I'm OK with the fuller brush static dissipater that Forespar sells.
You mount it onto your masthead with a couple screws.
However it can't work unless it is grounded. I'm guessing.
Our masts are deckstepped, so we have to create a path for ground.
Some guys talk about using 'welding wire' to make direct bonding connections.
I imagine that from the stem of this electric wick I'd connect it with welding wire to the two shrouds and the two stays. (What's the galvanic corrosion separation between stainless and copper?) The method of attaching the copper to the shafts of the dissipater and the rod is a problem.
I'd have a sharppointed Benji lighting rod that would also be connected in the same way.
Don't believe you can have one without the other.
At the turnbuckles on deck we have another problem.
I thought that a heavy duty alligator-clip battery cable could be attached to the wire above the turnbuckle and tossed overboard into the water. Backstay, forestay, and upper shrouds.
Aligator clips don't make a good connection.
However the static dissipater and the lightning rod aren't going to work unless there is
FOUR SQUARE FEET OF COPPER somewhere on the hull. Right, we need an absolute ground.
Don't know if it has to be 1/4" thick plate, or foil, or copper paint.
SO, can each of the four battery cables be altered so one square foot of copper is attached to the part in the water. I assume it could be a hollow square cube, or a plate, or some copper water pipe, or even a coil of wire? Would that take the place of 4 squares of copper attacted to the hull?
If any version of this seems feasible, can we talk about it? How to do it?
I know it's all conjecture but, specific to the Ariel/Commander, could this 'portable' system be effective at all?
www.kp44.org
Peterson Cutter Wedsite
scroll to the bottom of their Welcome page to their great list of articles and links:
Lightning Protection on Sailboats
Excellent questions! Here is a summary of what I've learned over the years. (In two parts due to size limits).
There are two short-but-good sources of information pertaining to lightning protection systems that I suggest reading before making an investment in time and materials:
Lightning & Sailboats, University of Florida, http://edis.ifas.ufl.edu/pdffiles/SG/SG07100.pdf. A good description of the behavior of lightning and basic design of a lightning protection systems for sailboats. (Free document.)
NFPA Standard 780, http://www.nfpa.org/catalog/product....order_src=B484. Contains detailed descriptions of recommended wire gauges, fastener types, etc., as well as good advice on technical design details. ($41.50)
A sailboat in seawater having a modest lightning protection system isn’t the worst place to find yourself during a thunderstorm. I once found myself in a metal rowboat in a freshwater lake named “Molnbyggen“ in northern Sweden; while Thor hurled lightning bolts from a rapidly developed thunderstorm directly overhead. I was surprised at how fast a rowboat can go with someone rowing for his life! Later, when I asked if the name of the lake meant anything in English, I was told: “Why, yes. In English it means: ‘the cloud builder’.”
Here are some basic principals I’ve learned over the years:
You don’t have to achieve perfection to gain some benefits. Any protection is better than none at all. When it comes to lightning protection, many people have a difficult time getting past a feeling of futility. But it’s not an “all or nothing” situation.
At the risk of stating the obvious, the likelihood of sustaining damage from lightning is inversely proportional to the distance of the lightning. More distance = less risk of damage. From a probabilistic standpoint, there’s lots of lightning at a distance, and much less nearby. So, if your lightning protection system is only capable of withstanding distant strikes, you’ve still solved most of the problem.
Since damage to delicate electronics like radios can be caused by a strike far away – while certainly not the ideal configuration - connecting a thin wire to the bottom of your mast and throwing the other end in the water will still dissipate the small induced currents caused by distant strikes that are much more frequently encountered, and it will also allow your mast to neutralize some of the difference of potential (voltage) between the mast top and the surrounding air. A small investment will protect your vessel and its electronics from most lightning hazards.
Cheap and dirty is better than nothing. If you buy an arc welding clamp, several feet of battery cable from which you remove all of the insulation, connect the wire to the clamp, connect the clamp to a shroud line or stay above the turnbuckle, and toss the other end of the wire into the water; you will have some protection from lightning.
Everything else I’ll write here is only a refinement of that design.
Use flat copper braid or (slightly better) copper strap wherever possible and avoid sharp turns wherever you can. Lightning is made up of mostly very low frequency (VLF) energy, with some minor radio frequency (RF) components spanning the entire radio spectrum into the gigahertz range[1]. Since lightning behaves like RF energy, the two factors you have to overcome are DC series resistance and RF inductive reactance. RF travels on the surface of conductors because of something called skin effect.[2] RF travels better on a flat conductor (like copper strap) than on a round conductor (wire) because the surface area (the “skin”) is greater with a flat conductor for a given amount of copper (you get better results for the same investment in copper). A flat conductor or plate also has less effective series inductance because of complicated conditions that would take a long time to explain. Suffice it to say that inductance is bad. The worst possible arrangement for conducting lightning would be a coil of wire. It would appear to lightning as effectively as if it weren’t there at all.
RF sees a sharp 90 degree bend as a quarter turn of an inductor, which detrimentally increases the impedance of the overall lightning protection system. This is why NFPA Standard 780 specifies a minimum radius for bends in conductors.
But referring back to point 1, don’t give up if you can’t use strap or avoid sharp bends.
Also, from a cosmetic standpoint, flat copper strap is usually easier to conceal flush to a surface than is round copper wire. After making sure you have really solid connections, feel free to paint the strap. By the way, if you run your copper bonding strap down the bottom of your bilge (which is a convenient way to interconnect the fore and aft halves of the vessel), don’t paint it. Any water in the bilge will slosh over the copper, and you may find your bilge smells better as a consequence. Copper has long been used to repel sea life from hull surfaces, but it is also a fungicide and bactericide – copper interferes with the metabolism of microbes. That’s a long topic by itself.
You want to use pure, electrical grade, copper for all conductors. I’ve never heard of using “welding wire”, but if it isn’t pure copper, avoid it. Since an aluminum mast represents such a massive lightning "downwire" to conduct a strike, I wouldn't fret over it being aluminum instead of copper. Just provide a really good bond at the base of the mast, and it'll do fine. Because of skin effect, it doesn't matter that the mast is hollow. If running a conductor from the mast base isn't convenient, providing a "water terminal" (submerged plate) at your stern, and connecting your backstay to that terminal is actually a good configuration because you can provide a smooth path to the plate that avoids any sharp bends. So far as the electrical properties for conducting lightning are concerned, I wouldn't worry too much about bypassing the turnbuckle, but you may have a mechanical problem after a hit: your turnbuckle may become seized by being welded in place. A clip-on bypass can be used when the boat is unattended and when you anticipate penetrating a storm. Be sure to provide a bonding wire from the plate to the rest of your protection system.
Use robust bronze clamps or brazed (silver-phosphorous-copper) connections. Do not depend on soldered (tin or lead-tin) connections. Solder melts at a very low temperature and has higher electrical resistance than copper. During a direct or close by lightning strike, most of the electrical heating will be concentrated at the soldered junctions (because of skin effect), and because of solder’s higher resistance, the solder will instantly boil and vaporize. Think of soldered connections as being fuses that “blow” during a lightning strike, opening the electrical connection that carries the lightning when you need those connections most. Lightning strikes consist of several repetitive “strokes” (called “restrikes”), and your soldered connections will vanish after the first stroke in a direct hit. But again, if you have to solder, we’re back to point 1 above. Don’t give up here! You’ll still get some protection.
The preferred materials for fasteners are bronze and stainless steel, in that order.
Assuming you don’t have an unlimited budget, tailor your investment to the actual risk (do a “risk/benefit analysis”). The west coast of the US is one of the safest places to be with regard to lightning, while the Gulf States and the southeastern Atlantic coast are the most dangerous. NASA recently produced a map based on lightning observations from space: http://earthobservatory.nasa.gov/IOTD/view.php?id=6679. While a more-is-better approach to lightning protection is valid, you can reach a point of diminishing returns where additional money is better spent on other safety items.
[1] NASA, Review of Measurements of the RF Spectrum of Radiation from Lightning: http://ntrs.nasa.gov/archive/nasa/ca...1987001225.pdf. Ever since Apollo 12 was nearly taken out by a lightning hit during launch, NASA has had a deep interest in lightning phenomena. Some very interesting background info on lightning can be found here: http://thunder.msfc.nasa.gov/primer/.
[2] Skin effect is a very substantial factor. In fact, even at the extremely low frequency of AC power – 60 Hertz – it’s pointless to use a wire thicker than 2/3rds of an inch because none of the current will flow through the center of a conductor that’s any thicker. In RF work, we often use hollow copper tubes instead of wire for conductors because a solid wire would be a waste of copper. If you ever have the opportunity to inspect something conductive that has been only slightly damaged by lightning you will probably notice that its surface is singed but its center is undamaged.
5. Bond every potential lightning conductor to a single-point ground. In the radio broadcasting business, we call that point the “common ground.” The old folklore adage that: “electricity takes the path of least resistance,” is just wrong. If it were true, then turning on whatever appliance draws the most current (has the least resistance) in your home would cause all of the electricity to bypass everything else. Then every time you turned on your electric oven in your home – all your lights would go out!
There’s something called Kirkhoff’s Laws that explain the effect in detail, but the short version is: when conductive paths are available, electricity flows through every one of those available paths. The current flow in each path is inversely proportional to the resistance of that path. More resistance = less current.
The reason you want to choose a common point ground is to prevent current from flowing through unexpected and inadequate paths. When that happens, it’s called a “ground loop,” and if you aren’t careful you can have thousands of amps flowing through a thin conductor that will get hot enough to ignite a fire or ruin expensive electronics. In installations lacking a common ground design, it’s not uncommon to see the outer braid (“shield”) of a coax cable become the primary path for a lightning discharge, and the expensive radio at the other end of that cable converted into so much charcoal. And the prospect of a fire at sea ranks at the top of my list of Things to Avoid.
You accomplish a common point ground design by selecting one point, and one point only, to connect all your circuits that should be at ground potential. That’s usually done with a buss bar or One Big Badass Bolt (the negative terminal on your battery is a good choice) connected to the biggest conductor you can afford, which is then connected by the shortest and straightest path possible to your ground plate submerged in the water. Everything metallic that could become a secondary path for lightning (engine, metallic through-hulls, keel bolts/cables, mast, standing rigging, battery (one terminal only please – commonly the negative terminal), etc., is connected by wires radiating from that common point. And if you're tempted not to ground some delicate piece of electronics while thinking: ”but these wires are insulated, so lightning can’t pass into them,” remember that the lightning already passed through several thousand feet of air to reach your vessel. A few millimeters of 600 volt-rated insulation won’t offer any realistic impediment.
Side strikes: When you hear stories like: “Lightning hit the house, and then flew from the fireplace across the living room into the opposite wall,” that’s a “side strike”. If you tore out the drywall, you’d find electrical wiring, a water pipe, or some other conductor directly beneath the point hit by the lightning. Preventing side strikes is another purpose for bonding everything together. A side strike in your boat could produce a hole punched in the hull below the water line, or worse, pass through you.
6. Provide as large a conductive surface area as possible through which to discharge the energy into the water. “More is better,” but the generally accepted bare minimum is 2 square feet. Please don’t consider using your propeller as the primary discharge surface, and then connect your lightning discharge wire (“downwire”) to the engine. The resistance between your engine and your propeller might measure “zero ohms” at the milliamp of current from a volt-ohm meter, but a lightning strike will cause an enormous current (often tens of thousands of amps) to flow through your engine’s main bearings, frying them.
Copper paint on your hull is great for repelling marine organisms. It is worthless as a lightning conductor. You need nearly pure copper to conduct electricity.
An added side benefit of all this efforts is – your radios will work better in a storm and during very low humidity conditions. Since the time that boats had masts, mariners have observed in darkness a bluish glow occasionally coming from the tops of their masts. They named the effect "Saint Elmo's Fire." The scientific name for the effect is "coronal discharge" and it requires several thousand volts of difference of potential between the boat and the air to generate this visibly glowing plasma -- which usually occurs exactly where you have mounted your VHF antenna. The current is extremely low, and the discharge shouldn't damage a well designed radio, but you'll be lucky if you can hear anything besides static on the receiver while it's occurring. Placing one of those "brush looking" static dissipators at the top of your mast will cause the discharge to opportunistically favor developing around the dissapator instead of around the tip of your VHF antenna.
Equipment sources:
These are reliable sources I have used in the past. You may find cheaper deals elsewhere, so I encourage you to shop around.
Copper plate, braided wire stap, copper buss bars, copper strap, bronze fasteners, and brazing rod. Georgia Copper: http://www.gacopper.com/.
Antenna lightning arrestors (use at the antenna end of the coax): Polyphaser. Superbly effective and used widely by the US military for, let’s just say, “other purposes” as well as for lightning protection. They are so effective in fact that it may be illegal to export their product to certain countries. Alpha Delta: These arrestors have replaceable arc chambers. I don’t recommend using them at the antenna only because you won’t want to climb your mast to perform an arc chamber replacement. But they are fine at the radio end of the coax. Both products are available from DX Engineering: http://www.dxengineering.com/Section...D=48&DeptID=19
Grounding plate: You don’t need anything fancy. An 18 inch X 18 inch copper plate will do. I personally hate through-hulls – I loose sleep over any hole I make in the hull. However, this is an interesting approach to providing a large surface area to ground: http://www.ropeantenna.com/Grounding%20Plate.htm. To avoid through-hulls, I hang two pieces of 2 inch wide copper bar stock, submerged 3 feet into the water, from the outboard engine port on either side of the engine. That combination provides 2 square feet of surface area (there are 4 surfaces on the 2 bars). I feel 2 square feet of surface area is adequate for seawater. In fresh water, you will need more.
If I haven't covered all of your questions, please advise.
-Patrick Bryant, S/V Jubilee, Ariel #75
FCC Licensed: Commercial Radio Operator, General Class; Amateur Radio Operator, Extra Class (N8QH); Global Maritime Distress and Safety System Maintainer with Ship RADAR endorsement
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