Striking Lightning Facts
An analysis of 10 years of lightning claims reveals which boats are most at risk.
By Beth A. Leonard
Published: January 2015
Photo: C. Clark, NOAA Photo Library
Lightning seems like the ultimate “act of God.” Unpredictable, capricious — it can come as a literal bolt out of the blue (or out of a glowering, black, anvil-shaped cloud). As the “Lowering the Lightning Odds” article in the July 2014 issue discussed, somewhere around one in a million people gets struck by lightning in any given year. Which means that someone must have it in for boats — two separate analyses of 10 years of lightning claims data from the BoatUS Marine Insurance files have found that about one in a thousand boats has a lightning claim each year.
When people get struck, it seems to be random. Yes, men get struck more than women (82 percent of lightning fatalities from 1995 to 2008 were men according to Popular Science), but that’s only because men spend more time outdoors and won’t stop what they’re doing for a little lightning. No one has yet suggested that tall people get struck more than short ones, or blondes are more at risk than brunettes. The same cannot be said for boats. The data shows that when it comes to lightning, not all boats are created equal. Certain boats are significantly more at risk than others. So which boats get hit, in which parts of the country, and how badly?
Table 1. The probability of a lightning
strike by type of boat, 2003–2013
Type of Boat Chances per 1,000
Multi-hull Sailboat 6.9
Mono-hull Sailboat 3.8
All – Overall Average 0.9
Bass Boat, Runabout, Pontoon Boat 0.1
While any boat can be hit — BoatUS Marine Insurance has even had some lightning claims for personal watercraft — lightning is most likely to go for that tall, tree-like metal pole sticking straight up toward the sky. The taller the better. That’s why sailboats have significantly more lightning claims than powerboats (Table 1), and almost certainly why larger boats have more lightning claims than smaller ones (Table 2) — overall size is closely correlated to mast height, which is probably what really matters here. And as far as lightning is concerned, two hulls are better than one. Multi-hull sailboats are almost twice as likely to have a lightning claim as mono-hulls. But that’s only true if that big, pointy thing is in the middle of the boat. The frequency of pontoon boat lightning claims is well below the average.
Table 2. The probability of a lightning
strike by size of boat, 2003–2013
Type of Boat Chances per 1,000
0-15 Feet 0
16–25 Feet 0.2
26–39 Feet 2.1
40–64 Feet 6
According to Martin Uman of the University of Florida’s Lightning Research Group, the average lightning bolt is an inch wide and five miles long. On the face of it, it seems unlikely that 20 or 30 feet more height — roughly the difference between the mast on a 35-foot and 45-foot sailboat — would almost triple the odds of the boat being hit. But understanding how the electrical charge that passes through a lightning bolt moves between the clouds and the ground makes lightning seem just a bit less capricious.
What To Do If You’re Caught Out On The Water
“When thunder roars, go indoors.” If there is time, return to shore and take shelter in an enclosed building (not open-sided) or your car. They are not impervious to lightning, but the lightning is less likely to do damage.
But if lightning has already begun, getting closer to shore may bring you close to trees and other objects that could be lightning targets. In that case, stay on the boat and do the following:
• Go indoors — go down below. Stay in the center of the cabin if the boat is so designed. If no enclosure (cabin) is available, stay low in the boat. Don’t turn yourself into a lightning rod!
• Keep arms and legs in the boat. Do not dangle them in the water.
• Discontinue fishing, waterskiing, scuba diving, swimming, or other water activity when there is lightning or even when weather conditions look threatening. The first lightning strike can be a mile or more in front of an approaching thunderstorm cloud.
• Disconnect and do not use or touch major electronic equipment, including the radio, throughout the duration of the storm.
• Lower, remove, or tie down the radio antenna and other protruding devices if they are not part of the lightning protection system.
• To the degree possible, avoid making contact with any portion of the boat connected to the lightning protection system.
• On larger boats with an oven or microwave, putting electronics inside should prevent them from being damaged as the oven or microwave will act as a Farraday cage, allowing the charge to pass harmlessly through the metal around the devices.
From University of Florida’s “Boating-Lightning Protection” by William Becker
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