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Old 12-07-2014, 08:34 PM   #1
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Metal thru hulls in fiberglass boats should not be bonded

Ok, tell me why they should.
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Old 12-07-2014, 08:54 PM   #2
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None of mine are in the bonding system and the boat is a 1976 model.

It used to worry me that they weren't. But the yard removed and tank cleaned the bronze engine intakes and strainers this fall during haul out and they were bright and yellow just like new. So I can't offer you a reason why they should be bonded??
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Old 12-07-2014, 09:01 PM   #3
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2 theories...both have plus and minus reasons.

I thought ABYC says to do it and the Europeans tend not to.

Calder describes both theories in his electrical/mech book.

I have seen both done and have had boats factory both ways. Can't see the reason to do all thru hulls myself but for some it's not a bad idea if close to other metals and routinely exposed to salt water/salt bridges.

Bottom line...throw a test probe on them and see if they need protecting.
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Old 12-08-2014, 11:02 AM   #4
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So if you get hit by lightning it will blow them out?
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Old 12-08-2014, 01:03 PM   #5
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Maybe an expert could chime in, but isn't bonding also is for the non bronze /dissimilar metal valves? And then how about the connection to the engine via seawater being pumped. Lots more to it than just a bronze through hull IMHO
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Old 12-08-2014, 01:22 PM   #6
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In order for a zinc to protect underwater metals, the zinc must be electrically connected to the metal, either by direct clamping like a shaft zinc or indirectly with a bonding wire from one metal part that is clamped to the zinc (the shaft, tranny and engine) or from an independent zinc (like a transom zinc). This connection forms a "battery cell" underwater and the less noble metal, the zinc preferentially wastes and the more noble metal- the shaft, prop or thruhull does not. That is the theory behind bonding wires.

Having said that, there is an underwater distance beyond which a zinc will not protect a bonded underwater metal, like a forward thruhull that is a dozen feet or more from the transom zinc. That distance is reported to be in the 3-6' range. I suspect that the theory behind this is that the sea bottom also acts like the other side of the battery and will ground the electrons produced so none will be there to protect distant metals. In most marinas the bottom is only 5-10 feet below the keel.

And finally bronze is a very non corrosive metal and if left unprotected may do just fine as noted above. Having said that I have had a bronze thruhull where the bonding wire had been broken for a long while, fall apart in my hands due to corrosion.

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Old 12-10-2014, 01:50 AM   #7
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I don't profess to be an expert

There are some large boat builders like Bayliner, Searay, Hatteras, that believe in bonding through hulls. These are big builders that have been building boats for long time. I don't think they would be bonding through hulls without reason. Bayliner for one isn't known for wasting money on unnessary stuff.
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Old 12-10-2014, 06:23 AM   #8
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Quote:
Originally Posted by Scary View Post
There are some large boat builders like Bayliner, Searay, Hatteras, that believe in bonding through hulls. These are big builders that have been building boats for long time. I don't think they would be bonding through hulls without reason. Bayliner for one isn't known for wasting money on unnessary stuff.
Throw in DeFever, Nordhavn, Selene, KK, and Fleming to name a few more. Is there not a compliance issue here for new builds?
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Old 12-10-2014, 08:55 AM   #9
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That's funny

Quote:
Originally Posted by pilothouse king View Post
So if you get hit by lightning it will blow them out?
My neighbor's boat got hit by lightning when we were in Portage Bay. Blew a hole right though the hull at water line on the Valiant and nailed the Advanti between us. Didn't blow out through hulls, did take out all of the electrical systems on both boats. Insurance repaired both boats. But again this is punny Pacific Northwest lightning. Not that southern US lightning you guy's get. How do you live with that stuff.
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Old 12-10-2014, 11:20 AM   #10
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I bought a 41' sailboat from a guy at Ocean Reef Club back in the mid 80's. He had removed all the factory bonding of thru-hulls from the vessel. I asked him why. His response "this boat was an insurance replacement from the last one that was struck by lightening as I was going up Biscayne Bay. It blew out the thru-hulls and sank immediately. Thank god it was shallow water and we just stood on the cabin top until rescued, but what if it had been out in the Gulf Stream". GOOD ENOUGH for me. :>)
I've been anchored many a time off Elliot Key in sailboats, in ferocious lightening storms. The ONLY boat there at all, and here I am with a mast sticking up 53' with lightening hitting the water all around me. There's no rhyme or reason (I can figure out) of why it doesn't strike. It's just one of those things you get used to down here. Maybe it's why it's called the Bible Belt? You can only pray.
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