Every year, hundreds of sailboats are struck by lightning. Although few of these strikes result in personal injury, damage caused to spars, rigging, electronics, and electrical systems can be counted in the millions of dollars. During the peak of the thunderstorm season in the late summer, marine surveyors and insurance companies are swamped with calls from sailors whose boats have been struck.
Ever since Ben Franklin foolishly experimented with his kites and keys, trying to catch lightning in a glass jar, we have understood that lightning is the result of the difference, or potential, between positive and negative electrical charges. What Ben didn't know was that these differences in electrical charges can be measured in hundreds of thousands of volts. The positive charges are usually higher in a cloud formation while the negative charges are lower, resulting in electrical current movements within a cloud, between clouds, or from cloud to ground. There is also evidence that the potential can travel in the opposite direction, that is from ground to cloud, meaning that the positive charges are accumulating on objects on the ground below the cloud.
The negative charges always seek their positive counterparts, but because air is a poor conductor of electricity, this buildup of electrical potential searches for a conductive path between the positive and negative charges until the energy is released in a sudden flowólightning. The basic precept to remember about lightning is that it searches for a conductive path to ground. Only when the insulation of the air can be overcome by huge amounts of energy is the electrical potential, or difference between positive and negative charges, released between the cloud and the ground as a lightning bolt. In the case of a sailboat, water is the "ground" and the lightning will use the vessel as its path to earth.
Lightning Protection Systems Many sailors believe that they are safe if their boat has a "lightning protection system," believing the term can be construed to mean "strike prevention." But the truth is that lightning protection systems are not capable of preventing lightning strikes. The real function of a lightning protection system is to direct the electrical discharge, if the vessel is struck by lightning, in a way that the likelihood of damage to the vessel or injury to the crew is minimized.
The issue of lightning protection systems is clouded further for many sailors because there are two schools of thought on protection for sailboats among lightning experts. One school holds that it is not necessary to protect a sailboat at all; the other accepts the value of lightning protection. However, and even more confusing, with the latter, there are many variations on what constitutes proper protection. Perhaps with a better understanding of lightning and lightning protection systems, each sailor can make more knowledgeable choices on whether to have a lightning protection system on board.
To Not Protect
|"The human body is mostly water, a much better electrical conductor than air."|
The thinking of the "unprotected" school is that by installing a direct path to ground, as in a lightning protection system on a boat, an invitation is being issued for a strike to come aboard. This is the great irony of deciding on lightning protection systemsóunprotected boats may actually be struck less often, but when they are struck, they usually suffer more damage. A boat with a good lightning protection system, on the other hand, may actually have a greater likelihood of being struck, but the strike is dissipated and directed away, usually with minimal resulting damage.
Metal is a well-known conductor of electricity, and aluminum and steel boats are likely to suffer less damage than wooden and fiberglass vessels, which are fairly good insulators. This is not to say metal-hulled boats aren't hit by lightning, only that they can dissipate the strike more quickly because of their conductivity to ground. For non-conductive hulls, particularly if the spar is aluminum and topped with a radio antenna, it's probably better to have a lightning protection system.
If you choose not to protect yourself, your crew, and your vessel from lightning, this decision should be made based on the old real estate maximólocation, location, location. The chances for a strike are very small if you sail in an area where thunderstorm activity is minimal. But if you sail on most offshore routes, or along the US East or Gulf Coasts in summer, especially in Florida, the chances of encounters with lightning increase dramatically. In these circumstances, a lightning protection system should be installed and additional safety precautions taken.
The most important thing to keep in mind about a lightning strike is that the human body is mostly water, a much better electrical conductor than air. You or your crew can become a path to ground, even if you're not touching any metal objects in the boat! This phenomenon is called "side flash," and it occurs when the electrical charge jumps from one conductor to another, always seeking (and finding) a better path to ground.
Being on board a sailboat during a thunderstorm poses an immediate danger to the crew, whether or not there's a lightning protection system. If leaving the boat for shelter on land is not possible when thunderstorms roll through, safety precautions should be taken immediately by the crew to minimize personal danger.
| ||Discontinue any exterior activities and move inside. Avoid any activities that might provide a connection between your body and the water, even something as seemingly minor as fishing.|
| ||Stay low in the vessel and move as close to the center of the boat as possible.|
| ||If possible, immediately disconnect all electronics, especially the VHF or any other radio connected to an antenna. Lower or remove the antennas if possible. Do not use any telephone, including cell phones.|
| ||Do not come into contact with any piece of equipment that is bonded to the lightning protection system, especially two components at the same time. Your body then becomes a path for electrical current if the vessel is struck. Keep away from all metal objects whether or not they're bonded to the system.|
| ||Do not go near the spar's compression post if it is deck stepped, and stay away from the spar itself if it is keel steppedóremember that this is the main conductive path.|
| ||If the vessel is struck, immediately check the seacocks and thru-hull fittings to be sure they're still intact. Always have wooden plugs on hand in a variety of sizes that fit the vessel's seacocks.|