Electrical grounding and outboards

[Tom Wootton]

Reading Don Casey's book on sailboat electrics, he describes a ground wire to the (inboard) engine block from the battery's negative terminal, thereby grounding the system through the propeller shaft to the water. Casey makes no mention of outboards. My outboard is connected to the battery's negative terminal through the negative lead from the electric starter/alternator. Does this ground the system through the motor to the water? If so, what about when the motor is tilted up? Am I not grounded? I keep the motor tilted up when sailing and in the slip; does this pose any dangers? Thanks in advanceTom

 

[Steve Dion]

I doubt that the outboard has anything.....

Tom:I doubt that your O/B engine has anything to do with the grounding of your electrical system. You do not NEED a motor on your boat at all. If you were to disconnect the batteries from the engine, the electrical still works. There is probably a ground somewhere else in the system. Maybe a thru hull or keel bolt etc.

 

[Tom Wootton]

Thinking out loud

Steve, you may be right, although my boat has no keel and no underwater thru-hulls. The only possibility would be the compression post, which is grounded to the water through the centerboard bracket. But as far as I can tell there is no such connection to the boat's wiring, at least according to the owner's manual. I think I'll try to contact the author. He has a column on the Sailnet website; I'll report back anything I find out.

 

[Ken Shubert]

Not Grounded

A good many outboards on 26's are not electric start so they don't have any connections. I haven't found any evidence of lightning protection on my H23.5 at all. It's a little worrisome when caught at anchor in a thunderstorm! It would probably be a good idea to carry a jumper-cable to clip on the mast and throw a good conductor overboard. I'd sacrifice the the companionway screen for that. Electricity behaves much like people and takes the path of least resistance.KenS/V WouffHong

 

[Tom Wootton]

Grounded (I think)

Ken, I am more familiar with the 26 but my owner's manual covers both the 24 and the 26 and I'm pretty sure that both have a direct path to ground for the mast thru the compression post and the centerboard bracket. It might be worth it to run the jumper cables from the SHROUDS to the water (You'd need 2 pairs of cables--3 if you include the headstay.) As you say, lightning seeks the most direct path, and it doesn't like to make sharp turns. I've seen mast-top devices (they resemble bottle brushes) which are designed to further reduce the electrical potential of the mast. We had one on a dive boat--we called it an elephant repeller (a slight dig at my cousin, who insisted on buying the thing.) It worked--we were never attacked by elephants, or struck by lightning either!