Jumper cables on board
Rig your own emergency lightning protection
By Dave Osmolski
In my 14 years as a vessel examiner, I have rarely seen a set of jumper cables on a boat, and I don’t carry jumper cables on mine. I carry four batteries, any one of which is capable of starting my engine. The odds of all four being depleted at the same time are miniscule.
Talking with my brother-in-law, a former sailor, got me thinking of sailboats and equipment. The day was stormy, and we were discussing a sailboat’s predilection for lightning strikes. We talked about using jumper cables as a means of directing the current from a lightning hit to the water. While not a perfect solution, it would be better than having lightning blow out a metal underwater fitting.
Lightning is a high amperage discharge of electricity at a radio frequency. The high amperage does the damage. If lightning hits your boat’s mast, it will instantly follow the path of least resistance to ground. If that path is through your leaded keel, that’s where it will go, perhaps taking your keel with it.
Jumper cables come in a variety of lengths, quality and sizes. Some inexpensive cables have small No. 12 AWG wire. The cables’ thick rubber coating misleads us as to the wire gauge. Usually low priced, these cables aren’t even very good for jumping from another battery. The wire’s resistance prevents it from delivering enough current to your starter. Other jumper cables have conductors large enough to deliver current to your starter, but they may not be enough to deliver lightning to the water.
Most hardware stores sell spring contact clamps that can be used for jumper cables, and many sell No. 4 AWG welding cable. Welding cable’s finely stranded wire provides flexibility and enhances conductivity.
To improvise your own solution, buy 20 to 25 feet of No. 4 AWG welding cable, four spring clamps, four No. 4 ring connectors and a package of 8-inch long black plastic electrical cable ties.
Cut the cable into two 10- to 12-foot-long pieces, lay them side-by-side and fasten them together with the wire ties within 12 to 14 inches of the ends. Solder or crimp the ring connectors to the ends of the cables, and, using stainless steel bolts, washers and Nylok nuts, fasten the cables to the spring clamps. On one of these cables, paint the spring clamps red. There you have it—a set of jumper cables that will double as lightning protection for your sailboat.
They will be pricey. The cable retails for about $3 per foot. If the cost bothers you, consider how much your boat is worth.
In the event of an electrical storm, clamp the cables to either the backstay or the forestay. Dangle the other end in the water over the side. If you have a chain rode on your anchor, clamp the spring clamps to the stay and the other end to the chain rode. Finally, always wash the cables and clamps with lots of fresh water after a dunk in salt water and use a quality water displacing oil afterward.
Lightning is powerful. Don’t expect this quick fix to provide complete protection. Always remember the cone of protection you learned about in Sail class. Don’t touch anything metal during a lightning event. Listen to your NOAA weather radio, watch the weather forecast, and don’t go out if it looks like a lightning event will happen.
D/Lt/C David H. Osmolski, SN, of Charlotte Power Squadron, has been repairing boats since high school when his first boat, a canvas-covered canoe with cedar ribs, leaked in gallons per minute and required constant repair.
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