Commonly Asked Question About Lightning


Is any purpose served by “interconnecting” all large metal objects on board?

Connecting large metal objects on board (called bonding) may help protect some gear, but is no guarantee. Surge suppressors wired between the positive and negative leads, and to ground, may help save some electronics. Suppressors are normally nonconductive, but when the “clamping voltage” is exceeded by a strike, the suppressor becomes conductive and shunts the charge to ground. They will not, however, have any effect on induced voltages cause by magnetic pulses, nor will they protect from the second zap because they are one-shot devices (like a fuse). But their greater value is in protecting crew, who may have no choice but to continue operating the boat. If metal objects are not interconnected, and a person touches two of great voltage difference, say the helm and transmission lever, a lightning strike will try to complete the circuit through his body. At the signs of an approaching thunder storm, the safest strategy is to secure the boat and go below, even if your boat is grounded and bonded.

For more information on installation of marine electrical systems, purchase Marine Electrical Systems, Vol. 2: System Installation from Practical Sailor.

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Darrell Nicholson
Practical Sailor has been independently testing and reporting on sailboats and sailing gear for more than 50 years. Supported entirely by subscribers, Practical Sailor accepts no advertising. Its independent tests are carried out by experienced sailors and marine industry professionals dedicated to providing objective evaluation and reporting about boats, gear, and the skills required to cross oceans. Practical Sailor is edited by Darrell Nicholson, a long-time liveaboard sailor and trans-Pacific cruiser who has been director of Belvoir Media Group's marine division since 2005. He holds a U.S. Coast Guard 100-ton Master license, has logged tens of thousands of miles in three oceans, and has skippered everything from pilot boats to day charter cats. His weekly blog Inside Practical Sailor offers an inside look at current research and gear tests at Practical Sailor, while his award-winning column,"Rhumb Lines," tracks boating trends and reflects upon the sailing life. He sails a Sparkman & Stephens-designed Yankee 30 out of St. Petersburg, Florida. You can reach him at