I wish I could say we had only owned our boat about five minutes before this incident happened, but two months would be more accurate. I still had not corrected a clear deficiency, and found myself as the poster child for electrical stupidity. It could have been a lot worse.

After the sparks died off, this is what I saw - one wing had melted off the wing nut on the negative terminal.



Anyone familiar with the American Boat and Yacht Council (ABYC) Standards will have a field day with this one. ABYC standards are used as guidelines in building, repairing, or surveying boats. They are “voluntary,” but are becoming more and more accepted as the industry standard when matters end up in court. They also make good sense, because many of them have been written in response to accidents that proved fatal to boats—and often to people as well.

In a nutshell, ABYC Standards state that batteries on boats must be installed in such a way that:

  • Any leaking electrolyte will be contained

  • The battery will not move more than an inch when pulled in any direction

  • The positive terminal is protected (with a boot or box cover) to prevent unintentional short circuits


Also, wing nuts are only allowed if the battery cables are size 8 AWG or smaller. If possible, they shouldn’t be used at all, but this is to accommodate those who need to remove and recharge batteries used for small things - like trolling motors, etc. There are other standards too – these are just the ones relevant to this story.

Scene of the crime, and the weapon.



So there I was onboard the boat fiddling with things on a Sunday afternoon. The batteries were in boxes with covers (good), and they were strapped down but a little loose (well, OK). However, wing nuts were used at the cable connections (very bad . . .), and it’s impossible to get them really tight by hand. I decided to check the batteries, and opened one of the boxes. The cover had been serving as the protection for the positive terminal, rather than having a boot over that connection, so once the cover was off, there were two terminals in the open.

The wing nuts weren’t very tight, so I grabbed an adjustable wrench to tighten one. I was probably daydreaming about something more important I had to do onboard when suddenly a fireworks display broke out on top of the battery – sparks flying everywhere. I jumped back, and it stopped after a few seconds. It was one of those “holy ____!” moments that leaves you terrified and exhilarated at the same time – hands tingling, heart pounding and a little giddy at being “shot at without result.”

I had accidentally let the wrench form a “dead short” on top of the battery by touching the positive post as I was tightening the wing nut on the negative post. A closer look revealed how lucky I was. When I tried to pick up the wrench, I discovered it was welded to the positive terminal and had to be pried loose. And the fireworks had stopped only because the wing of the wing nut had melted off. Without that happening, the heat would have built up quickly – perhaps causing a fire or explosion.

The wrench is no longer useable, except as a reminder to me and my kids of the power of electricity.



Speaking of welded, the jaws of the wrench are now permanently joined by the (former) wing of the wing nut. I suppose I could cut them apart, but I think this wrench is now worth more as a reminder for me, and a lesson for my kids if they ever say, “But Dad, it’s just a 12 volt system, right?”

For more (chilling) information on batteries, look up “battery safety” on the internet, or check out books by Ed Sherman or Nigel Calder on marine electrical systems. Batteries give off hydrogen gas when charging, and there are cases of serious injuries from battery explosions caused by a single spark at the wrong time. Battery acid can burn your eyes and your skin, so use safety glasses. If you do get some in your eyes, rinse with plenty of fresh water. Baking soda can be used to neutralize acid that gets on your skin or elsewhere.

Editor's Note: This story is part of a series on buying a used J/35.

Paul Grimes is an engineer and marine surveyor living in Portsmouth, RI. For more information, visit the Grimes Yacht Services website.