Lightning, Sailboats and the Power of Points
Multihull masts need grounding, too!
By Bobby Jepson
“Our president is a lightning rod for political criticism!” That might be something you’d read or hear most anywhere these days. What does that mean? Does it mean lightning rods attract lightning? Look that up: “Do lightning rods attract lightning?” You’ll find that’s not the case. The response might be so firm you’d think it a dumb question. But our vernacular betrays the disclaimer.
Many years ago, the folks that made lightning rods were advised by their first lawyers to not ever say lightning rods attract lightning: “Sweet Jesus, man, you can’t say that!” And if you think about it, it makes sense. What insurance company wants to be liable for damage to a proximate, uninsured property? They had a problem.
So the explanation of how lightning rods work evolved into “Lightning rods take lightning strikes safely to ground,” and if you had any doubt there are plenty of photographs of the Empire State Building getting struck by lightning, with no damage. Even Charles F. Chapman, writing in his textbook Piloting, Seamanship and Small Boat Handlinga century ago, said you’re in a “Faraday Cage” when of course you’re simply on a sailboat under a grounded lightning rod. But to say a mast is a lightning rod would invoke the notion that the lightning rod would take a strike, and it is most unlikely to do that. My guess is they had a meeting, and decided that calling sailing “being in a Faraday Cage” would be a good idea.
Oh, what a tangled web we weave
When first we practise to deceive! Walter Scott in Marmion
What Benjamin Franklin learned between 1743 and 1752 culminated in the invention of the lightning rod and more importantly his publication “The Power of Points.” By then, everything Franklin wrote was significant, he was certainly one of the finest writers in America, and master of a loose syndicate of printers anxious for something good to print. “The Power of Points” was soon translated to French and his experiments replicated in France, the center of the modern scientific world. Almost overnight he became a worldwide superstar, a pioneer of the Enlightenment, when at last all answers weren’t provided by either the King or by Rome.
Books have been written about Franklin’s remarkable electrical apparatus and methodology. He was the perfect man for the job: inquisitive, wealthy, and easing out of his successful printing activities. He knew everyone, especially artisans of his group of Philadelphia craftsmen, the Junto. He was affable, never confrontational, and quite possibly the most accomplished man you will ever encounter in history.
To our point here, he had mounted on his roof in Philadelphia a 9-foot iron rod, insulated by glass, which was connected by wire down into the stairwell in his home. There on the wall he mounted two brass bells some inches apart. To one bell he attached the wire from the lightning rod, to the other a wire which ran to the basement below and fastened to the well pump. Between the two bells, suspended by a thread, was a small brass ball. The simple device became known as Franklin’s Bells, although he got the idea from an Austrian who devised it ten years earlier. When there was charge in the air, the little brass ball would oscillate between the two bells, making them ring. Can you imagine why? Franklin did! And what do you think happened thereafter? In Franklin’s words, from his autobiography:
“One night, awakened by loud cracks on the staircase, starting up and opening the door, I perceived that the brass ball instead of vibrating between the bells was repelled and kept at a distance from both, while the fire passed sometimes in large quick cracks from bell to bell, and sometimes in a continuous dense white stream as large as my finger, whereupon the whole staircase was enlightened with sunshine so that one might see to pick up a pin.”
So there it is. Instead of just being there to take a lightning strike safely to ground, lightning rods pump a huge opposite voltage into the air above via induction. A pal’s dad, a farmer from Southern New Jersey, told my pal the lightning rods on their farm buildings “sucked the energy out of the clouds” and that’s a great layman’s explanation. In industry it’s called ionized air, and most static problems these days can be solved with grounded conductive fiber brushes. You may see a fuzzy wire next to the slot where the paper comes out of your computer’s printer; same thing there.
The elephant in the room is if you acknowledge you’re ionizing air above your lightning rod or sailboat mast, might that (positively) charged air serve to attract (negatively) charged air, i.e. lightning, to the proximity? Aye, matey, there’s the rub! That is why you don’t buy one lightning rod for your home; rather they’re placed every 12 feet or so along the ridge, and on the outbuildings too. If you see a lightning rod installer at your neighbor’s, call to him and get a quote! While on the subject, the ground wire cable for a sailboat mast needn’t go straight down any more than the cable for your home’s lightning rods comes down through your living room.
With the advent of iron ships, then yachts with aluminum masts that set upon metal keels, it was impossible to have a mast that wasn’t an effective lightning rod. The huge voltages involved don’t care about some bottom paint or a little anodize on the mast. But fast forward to modern keel-less lightweight designs married with the disinformation on the subject, and you’ll get what we have now: a bunch of lightweight sailboats out there with ungrounded masts.
The masts on most multihulls aren’t very big, nor very tall, and they really don’t present a very attractive invitation to the charged air above. The problem arises when you moor next to a conventional keelboat with a grounded mast. I was on a conventional sailboat years ago when we encountered a violent electrical storm, and lightning struck around the boat in a constant 50-foot radius every few seconds.
Remember Chapman’s “cone of protection” beneath the mast? Where that cone met the water, all hell broke loose. And what if we had passed a multihull sailor as we headed in? A very bad situation would have occurred!
There is absolutely no advantage to not grounding your mast. Even if the ability of your grounded mast to ionize air is overtaxed, which is extremely unlikely, there should be no damage as we see with occasional strikes to skyscrapers.
The best way to ground your multihull’s mast is permanently using a minimum of 144 square inches of 3/16" metal below the waterline, connected by at least #4 wire to a rod that extends above the top of the mast, per the recommendations of the U.S. Coast Guard. Alternately, for a temporary solution, get a stout 1/2" diameter aluminum cable as sold by lightning rod suppliers. You can either wrap it around your aluminum mast and throw an end off each side on the main hull (trimarans), or straight down into the water (catamarans).
Alternately, or if you have a carbon mast, attach a halyard about a foot or so from the end of the aluminum cable and run it up along side the mast such that the cable end is above the top of the mast. In each case, you want a couple of feet of cable in the water. I unwove mine such that the end in the water is like a broom. We’re dealing with single polarities of high voltages, and it’s trying to get away from itself, like the brass ball in Franklin's stairwell that night.
The cable I used cost about 65 cents a foot, making it a great way to spend $20. You’ll be able to equip a few boats in order to meet suppliers’ minimum charges.
Please ground your masts, and minimally get some aluminum cable aboard that becomes an important safety accessory like a life jacket or fire extinguisher.
Bobby Jepson is a New England Multihull Association member who, in his words, “squandered much of his career in the static control business.” He speaks on the subject, and is nearing completion of his book, Lightning, Sailboats and the Power of Points. Known to his friends as “Bobby Hot Rods”, he says, “I spent a lot of time enjoying hot rods all my life, and still have a project in the garage, but spend some of that time now on my Corsair 27, Triptych, in Buzzards Bay.”