Question re Grounding the Mast - SailNet Community
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post #1 of 11 Old 04-17-2010 Thread Starter
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Question re Grounding the Mast

I am looking to ground my mast to a keel bolt and have a quick question. Is there a recommended way to attach the ground wire to a keel bolt? Nigel Calder's description is vague about this, but says something about perhaps having to custom manufacture a copper washer to use as an attachment point.

Is there a reason I couldn't just use a battery post clamp? I plan on using #4 gauge wire and don't have easy access to a crimper for this size wire. Is there a reason I can't just by a pre-made battery cable and clamp it to the keel bolt with a battery terminal?

Thanks in advance!
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post #2 of 11 Old 04-17-2010
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Are you looking to ground the mast as part of a lightning grounding protection system? What kind of boat is it? Is the mast deck stepped or keel stepped—sounds like a keel-stepped mast, but still confirmation is good?

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post #3 of 11 Old 04-17-2010
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I doubt you will find a battery cable or lug with a hole sized for a keel bolt. I believe that is whu Nigel Calder suggests custom.

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post #4 of 11 Old 04-17-2010 Thread Starter
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I agree that I won't find a cable with a lug sized for a keel bolt, but that is why I was thinking of a battery terminal.

However, thinking about this further, if I use a battery terminal it will damage the threads on my keel bolt. So I think I need to make up a custom lug and then put another nut on the keel bolt and tighten it down.

Answers: Yes, keel stepped and lightning grounding is what I'm looking to do. Keel is external lead keel with silicon bronze keel bolts.
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post #5 of 11 Old 04-17-2010
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One good way to attach a lightning ground to the keelbolts is to drill and tap the keelbolt with a small screw...say a #10. Most keel bolts are of sufficient diameter that this isn't an issue, especially since the tapped hole doesn't have to be very deep...say 1/4" or so. Then use a silicon bronze machine screw to attach a ring terminal to the keelbolt.

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post #6 of 11 Old 04-17-2010 Thread Starter
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Tapping the top of the bolt would be an elegant solution, but I don't have a lot of experience using taps. My concern would be drilling the initial hole and not getting it nice and straight. Wouldn't this be difficult to do with a hand held drill?
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Yes, difficult if not impossible. Best to do it the Calder way and make it from a large washer held in place with a second nut.

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In bronze, which is a relatively soft metal...this is not difficult to do.

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Tapping the top of the bolt would be an elegant solution, but I don't have a lot of experience using taps. My concern would be drilling the initial hole and not getting it nice and straight. Wouldn't this be difficult to do with a hand held drill?

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post #9 of 11 Old 05-03-2010
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If you ground the mast to a lead keel, you may create galvanic corrosion issues, as the lead keel is at a different potential than other underwater metals like your SS propshaft and bronze propellor. You will need to make sure that the mast is not connected to any other boat ground--a common problem is the VHF antenna mount.
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post #10 of 11 Old 05-03-2010
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sd, do you really think a #10 screw is going to still exist after a lightning strike?

I'd suggest a tin snips and a sheet of bronze or copper scrap followed by a little handwork, to make a "washer" and crimp connection that are robust enough to last a little longer.

Plumbean, I think most battery cable terminals are still lead. Again, they'd just melt apart after a first strike. The ones that aren't lead tend to corrode and not conduct terribly well. Still, if you can get a good connection with good contact area, and grease it up so it doesn't corrode....beats nothing at all, doesn't it?
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