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.
