Lightning protection a qualified successJan 1, 2003
|From Ocean Navigator #66 |
Wings had been purchased the year before, and we had scheduled the voyage because Bill had to be in Lisbon in August for business reasons. Unfortunately, because he had to be there on August 9th, and the boat simply was not ready to go in time to make it, the trip had to be postponed until next year. Instead of returning through the N.Y. State Barge Canal to again winter the boat in Buffalo, we decided to put up in the Chesapeake for the winter to enable an early start next year. So, with four aboard, we set off for what we thought would be the relatively easy sail from Nantucket to Norfolk, with at least a chance for serious sea trials of a much-modified vessel.
We caught the noon tide at Nantucket and took Muskeget Channel. By nightfall we were well out to sea and trying to settle into what was clearly going to be an extended period of close-hauled sailing. Shortly after midnight Bill was awakened by Greg Dusky and Albert Hanneman, who were on watch. Because of the increasing winds and distant flashes of lightning, they had already dropped and secured the genoa. He immediately called for a double reef in the main. So, underpowered with just staysail and reefed main, we bobbed along and prepared for the worst. We didn't have to wait longsoon we were reaching off in winds that quickly built to 40 to 50 knots. The seas, which had been building, were flattened by the intense rain. The entire experience was quite exhilarating, especially the spectacular fireworks displayin spite of the ever-decreasing time between flash and thunderclap.
Our exhilaration quickly switched to concern when the bight of the reefed main filled with water. (We have always debated the merits of tying in the nettles, but never again.) Greg and Albert were having difficulty in emptying the sail, and we worried it would tear under the combined strain of wind and weight of water. Our preoccupation with the main and its sad state came to an abrupt end when suddenly we were simultaneously blinded and blasted by a lightning strike on our vessel. Every instrument on board the vessel went outincluding the apparent wind indicator we were using as a steering reference. In the confusion, the boat gybed and the water-filled main knocked down the canvas dodger. It seemed an eternity (probably less than a half minute) before we could get the boat under control again.
During the panic, the propane sensor was triggered. Its piercing wail contributed to the sense of alarm until finally April was able to reset it. The gybe had nearly emptied the main, and the job was quickly finished. Then, one by one, with no intervention from us but presaged by the propane sensor, the rest of the instruments began to return. The sequence of events was as though one had unplugged a computer, then watched it reboot, turning on and testing one component at a time. After several minutes, the entire complement of instruments was functioning againincluding the VHF and radar!
The refit of Wings had included both addition of a No Strike charge dissipater at the masthead and rewiring most of the boat. After several summers of sailing on the Chesapeake, we had acquired a great respect for both the winds and the lightning that intense thunderstorms can inflict. Two years ago we spent 20 minutes reaching off in Hobo, an Irwin 28, with winds in excess of 80 knots. Just a year ago we saw a tornado remove a portion of a roof from the Day's Inn not 50 yards from where our boat was docked near the Hampton Roads tunnel. These experiences gave us confidence in both our sailing abilities and strategies. Together with a terrifying lightning storm in the Mobjack, they also provided a certain urgency to our investigations of how to best protect a boat from lightning. As a result, we invested considerable effort in making sure that the bonding system included all metal on the boat. Moreover, our friend, and sometimes crewmember, David Zielkewho had wired in the Ample Power Emon II, the Heart Inverter, and our radar (and about everything else for that matter in exchange for my editing of his Ph.D. dissertation)had a passion for large ground wires (nothing smaller than 1/0 for the busses!). Great care was taken to eliminate ground loops, poor contacts, etc., or anything that might compromise the efforts of the manufacturers to shield their products. As a consequence, we would seem to have abided by both the letter and spirit of those who advise the best ways to avoid lightning strikes and to minimize their effect should they actually occur.
The properly prepared boat has three levels of protection. The first tries to reduce static electricity in the vicinity of the masthead by bleeding off electrons. The idea is firmly grounded in physics theory and can be implemented in a variety of ways, all of which depend on the fact that charge is conducted away from a very sharp point. In fact, the more points, the better. We opted for the No Strike, not because of its manufacturer's claims or its warranty, but because of its robust construction. The idea is to reduce the possibility of a stepped leader forming (the initial channel through which the main bolt then travels), and to minimize its strength if it does form. The second part of the protection system provides a path out of the boat. The aluminum mast does a wonderful job of getting the strike current to deck level, but what then? There must be a path to the water and the bigger the better since the electricity from a lightning strike travels on the surface of a conductor. Plus, there must be adequate conductor surface exposed to the seaconsiderably less of a problem in salt water than fresh. Finally, all the metal in the boat must be at the same potential to prevent arcing from one component to the next. This is important, not just for the rigging, wheel, etc., but also for the electronic packaging. In our case, the bonding system served both these functions.
While our experience might be a lot different the next time out, this time we survived with no damage at all. The fact that all the microprocessors on board shut down makes it clear that these systems were well aware of an attack. That they survived and were able to function indicates that the protection system worked as planned. Neither they nor the crew suffered any damage from the strike.
Why should this be surprising? Airliners suffer lightning strikes all the time with little or no damagethe reward for meticulous preparation. Our experience, admittedly anecdotal, seems to indicate that if sound principles are invoked and the deductions from them followed, then yachts can be similarly protected. There simply is no scientific basis for believing, as many appear to, that no preparation at all is the best approach. After considerable effort to understand why anyone accepts this as true, it is our opinion that this view is based more on manufacturers' wishes to cut costs or on survivors' tales than on real data. There are, of course, motorcyclists who survive crashes without helmets, and people without seatbelts are indeed occasionally thrown free from autos. Such statistics, however, are biased by the absence of reports from those who did not survive to give their stories. So it is with lightning: the principles of protection are for the most part understood and work more often than not. As our experience amply illustrates, boats, like planes, can be protected, as can their passengers. Bill's hands were on the steel wheel at the time of the strike!
Our euphoria at surviving the lightning more than compensated for the next two days of miserable sailing hard on the wind. After the storm passed, the winds dropped to the mid-teens, then over the next two days built back to more than 30. Then the GPS quit (a bad splice) and the solenoid for the propane stuck closed. These failures were minor annoyances, but they confirmed our decision to postpone the transatlantic. Finally, tired of the cold food and waves breaking into the cockpit, we declared the sea trials a success and bore off for Sandy Hook. After a day of recuperation and repairs, we once again set out for the trip down the coast. The magnificent trip was marred only by a brief squall shortly after leaving. While deeply reefed and close hauled, we were nearly run down by a commercial vessel off Highlands, N.J. Although well out of the channel and overtaking us, he neither obeyed the rules nor responded to hail, and almost succeeded in thwarting our best efforts to avoid him. For the next retrofit we are contemplating addressing this safety problem by implementing the suggestion of a fellow sailor (and international arms dealer): anti-tank missiles!
Bill George and April Howard live in Buffalo, N.Y., where Bill is a professor of mechanical and aerospace engineering at SUNY Buffalo.Edit Module