Lessons in lightning


A voyaging boat can expect one lifetime lightning hit, but the chance increases dramatically in hot, humid places, like the Intertropical Convergence Zone or Florida’s lightning alley, where as much as 20 percent of boats suffer some lightning damage every year.

It happened to us on June 7, 2011, while sailing in the Baltic along the north coast of Poland. We were underway aboard Onora, our 63-foot aluminum, Chuck Paine-designed cutter that had carried us from New Zealand where she was built by Kelly Archer.

Onora’s masthead wind transducer after the hit.

The Polish shore was a long low golden beach of impressionist hues unspoiled by development. I was pleased with the shape of our new main and reacher, which were making good use of the 12 knots of wind. The gentle offshore breeze was pushing out wavelets that lapped our bare aluminum hull. I ignored the cumulonimbus clouds — they were well inland — not wanting anything to ruin this perfect day.

Thirty minutes later Jeannie, my wife, remarked on the approaching clouds: now rising into majestic columns, thickening, and turning an angry gray. Soon the blue skies lost to these bullies moving in our direction like a charging wall of linebackers. They blocked the sun, covered the sky and began throwing lightning bolts into the sea around us.

Jeannie was nervous, and, as captain, I felt duty bound to chase away her fears; a panicked crew is not effective. Thus began my lightning anxiety calming lecture: “Our 85-foot mast is a target, but it gives us a circle around the boat, the diameter of which is equal to its height. If lightning intends to strike within that circle it will seek the mast which would be hit, but it is grounded and we would be protected. Beyond the circle, the water is the closer ground, so we are only threatened by a strike destined to hit within 85 feet of our boat. In my 66 years I have never seen a lightning bolt hit anywhere near that distance away from me. The danger is not worth worrying about.”

Jeannie seemed unconvinced, but I thought my logic was being borne out. The darkest clouds had passed to seaward, bound for Sweden. The period lengthened between the flashes and booms. Then we were hit by a downpour. We moved into the shelter of the pilothouse where Jeannie took the watch and I returned to planning our approach to Darlowo, a resort town at a river mouth 20 miles away.

Then we were hit.

The explosion, with a blinding flash and deafening CRACK, happened so fast it caught us completely by surprise. I watched in stunned silence as Onora’s wheel whirled to windward. The downdraft flogged the sails as though possessed and the boom thrashed like a hooked monster.

Jeannie recovered first, dashing to the cockpit where she grabbed the wheel and swung us back on course. My shock turned to panic: we could be sinking. I bolted below and grabbed up the floorboards to check the bilges. To my relief, they were dry. No holes had been blown in our bottom; we were not in danger. We could sail on and fully assess damage once we reached port.

Jeannie in the pilothouse. The boat’s autopilot was damaged and replaced with twin units.

By five that evening we were safely tied up along a promenade filled with smiling Polish families posing for pictures with Onora as the backdrop. I was crawling around the deck picking up black plastic bits and staring into the sky wondering where they came from. I climbed the 85 feet to the top of the mast to find that all that remained of our wind transducer was a toasted circuit board dangling in the breeze. Incredibly, the VHF antenna and masthead light were untouched.

Later that evening, after I’d checked every system, I visualized the damage. The charge that exploded the wind vane must have run down the wiring inside the mast to the saloon junction box, where a surge went forward to destroy the depth and speed transducers but, fortunately, did not blow them through the skin of the hull.

Another spike split off to the GPS distribution box where it zapped the Navtex and the signal converters that feed data to our two notebook computers. Much to our relief, however, the laptops, VHF, GPS, and SSB transmitter, also wired to that box, were spared any damage. Meanwhile, at the back of the engine room, the Icom HF/SSB antenna tuner on the starboard side and the WH Autopilot on port were damaged. I puzzled over these last two. Unlike most autopilots, ours is not connected with the other instruments; furthermore it is cradled within the shell of our aluminum hull, yet it and the isolated antenna tuner were damaged.

I reasoned that Onora’s aluminum hull with its enclosed pilothouse had kept Jeannie and me safe. Other than the damage to our nerves and my reputation as a ‘know it all,’ we personally felt no effects from the charge.

The next day, after inquiring with B&G, I received a rapid but discouraging e-mail response: All of the h1000 instruments including the wiring would have to be replaced. Furthermore, this system was obsolete.

Alfred Wood

While underway in the Baltic off the Polish coast, Onora was struck by lightning. The Foleys headed into the nearby  port of Darlowo for repairs.

I considered the option of halting our cruise to repair the damage and discussed this with Jeannie. Poland is just developing pleasure boating services and, since arriving in the country, we had met only one person who spoke English. Even if we found competent help who could understand us, we would still be at the end of the line behind fishing boats, local pleasure boats and technicians’ summer vacation plans. On the positive side, we still had GPS and a back up autopilot.

We decided to continue our planned trip in the Baltic’s short summer to Sweden’s northern Höga Kusten (High Coast) and the Gulf of Bothnia. Repairs would have to wait.

Learning about lightning
Meanwhile, I set out to discover the secrets of lightning protection by opening my onboard copy of Nigel Calder’s Boatowner’s Mechanical and Electrical Manual. The book further explained the cone of protection and some theories behind lightning. One setup for lightning is when positively charged ions are formed by water droplets freezing when sucked up inside cloud columns, leaving behind a negative charge at the bottom. This negative charge builds up until it is attracted by an opposing positive charge, which could be at the top of the cloud or on the ground. I found it interesting that the ground charge jumped from the boat up and does not always seek the nearest ground. The book went on to cast doubt on all prevention and some protection devices.

This further piqued my interest and I decided to visit the Annapolis Sailboat Show that October, where I could shop for new instruments and lightning gadgets were on display.

Once there, I talked to a maker of lightning dissipater devices, but remained skeptical. My discouragement lifted when I saw Calder himself and immediately introduced myself as a sailor whose boat had been hit by lightning.

“Fantastic, tell me about it,” responded the enlightened man with the beard. So I did.

One approach to lightning protection is from the company Marine Lightning Protection which includes side terminals called siedarc electrodes.

I ended with my questions: “Now, what should I do? Do dissipaters work? Surely Benjamin Franklin was on to something, and we must know more today than he did 200 years ago.”

Calder was not encouraging. He went on to tell stories about lightning jumping around in unpredictable ways. I have to admit that I was more confused than when I arrived.

I returned home to search the Internet. I had thought that any charge would run outside of our rigging but, because aluminum is a better conductor than the stainless steel shrouds, the current more likely returns down to the bottom of the mast where side flashes jump out looking for a path to the water. A fiberglass boat with an aluminum mast typically has a cable that runs from the mast’s lowest point to a ground plate exposed to water, but experience has shown this can be insufficient to drain all of the current, which often darts around the cabin, where it has been known to hit crewmembers wearing wet socks. These side flashes can be fatal if a crewmember gets in the way.

Next, I consulted a book by Dr. Martin Uman, The Art and Science of Lightning Protection, which impressed on me the magnitude of the force. Ninety percent of the strikes are 10,000 amps or higher — just 10 volts can fry a microprocessor.

Dr. Uman points out the safety offered by a metal box (Faraday cage). Boaters have long known the galley oven as a safe place for instruments but when the storm hits, I bet few of us actually use it. Dr. Uman goes further to suggest that the boat have a portable copper cage on board that, at the first sign of an electrical storm, the crew would assemble and climb into and remain for 30 minutes after it passes. This does not strike me as practical. It takes us a day to cross the convergence zone. Even if the boat can sail itself, I can’t see the crew in the cage drawing straws to see who has to go get sandwiches and water.

He addresses the faulty argument held by some that an unprotected boat provides no electrical path making it less likely to attract lightning. The data from Florida surveyors shows otherwise. An ungrounded boat is just as likely to receive the blow, but more likely to suffer serious damage, including large holes in the hull.

After repairs, Onora had a new air terminal at the masthead.

The expert
Both the Internet and Dr. Uman cite Dr. Ewen Thomson at the University of Florida as the expert on marine lightning. I decided to track him down. The school told me he had left academia to found a company, Marine Lightning Protection. I dialed the company’s telephone number and Dr. Thomson answered the phone.

He started his company to guard boats based on the theory that the ground charge does not go through the water down to China but spreads across the surface. He protects fiberglass boats by fitting electrodes at the waterline that are connected up and over the cabin top to the mast at deck level. The idea is to route the charge outside of the cabin, away from the crew, and he has evidence that it works.

Following his research, the National Fire Protection Association recently changed its standard from a single grounding plate to the bottom of the mast. It now calls for grounding the mast at deck level to a continuous loop outside of the cabin connected to multiple cables down to the grounding plate and supplemental electrodes.

Metal boats with an aluminum mast, like Onora, already have the whole surface of the hull as a ground, but carbon fiber masts need a lightning rod with a thick cable to the deck to attach to the loop and down to the ground plate and electrodes.

Dr. Thomson is currently working on saving the wiring and electronics. He told me that my old NMEA 0183 had a problem in that 0183 uses the shield for a common ground, an easy path for surges down the mast; likewise for antenna cables and mast light systems that share a common ground wire.

To correct this he is designing a junction box filled with surge protectors, one for each antenna, signal wire and power line, matched to each unit’s characteristics. It will be located at the base of the mast to clamp high voltage and shunt the spikes to the ground, however, for maximum protection, these devices should be repeated where the cables attach to each specific piece of equipment to catch voltage spikes induced along the way. Even then a magnetic field of vertical current can spread out in a loop from the aluminum mast or ground cable and knock out circuit boards just about anywhere on the boat.

In Dr. Thomson’s opinion, the fact that we were in the metal-enclosed pilothouse when the lightning hit just might have saved our lives.

Jim and Jean Foley live aboard their aluminum sloop Onora.

Lessons learned

1. Have good insurance. Our insurance policy covered 100 percent of lightning strikes. Keep the evidence until their surveyor agrees it is lightning damage. If you have extensive damage you might consider hiring your own surveyor to negotiate on your behalf. There are things I missed.

2. We were lucky to sacrifice our autopilot instead of a helmsman. If one must steer in a lightning storm, do not use two hands on a metal wheel.

3. In the next electrical storm, if Jeannie is not baking bread, I will put one of our laptops (both have full navigation capability) and a handheld GPS in the oven ”Faraday cage.”

4. If Nigel Calder doesn’t know how to prevent a lightning strike, I don’t think anyone does.

5. I will add a mast junction with surge protection.

6. I have installed a lightning rod.

7. I will listen to my wife.


By Ocean Navigator