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Old 09-04-2009, 13:21   #1
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Yikes! Thru-Hull Corrosion!

Has anyone seen an accumulation on a thru-hull like this before? Causes? The valve body looks very silver in the photo, but I believe that's an artifact of the flash.

Also, Beneteau tells me that all their thru-hulls use BSP threads. Seems like that little gem isn't well known. Somewhat addresses the "mismatched threads" argument for using NPT ball valves directly on NST thru hulls. This one says "Basic" on the handle. Anyone know the manufacturer?
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Old 09-04-2009, 14:11   #2
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It's most likely just very slight weeping of salt water through the threads.

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Old 09-04-2009, 16:14   #3
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I would venture the guess to be "APOLLO". It looks like their valve but the name on it doesn't 'ring any bells' and I work with their product line almost on a daily basis. It also looks like a stainless valve. (correct?) with a yellow rubber coated handle?
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Old 09-04-2009, 17:41   #4
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That's

That's an odd place for a hose clamp..??? Why is it there?
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Old 09-04-2009, 18:07   #5
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It's probably holding a bonding wire to the thru-hull. Waste of time IMHO. Something looks really wrong with this set up. That thing has to come apart!
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Old 10-04-2009, 05:39   #6
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The valve looks like stainless in the photo, but in actuality it appears more copper-ish in reality. The flash seems to wash out much of the color. The handle is red, not yellow. And the hose clamp is there to hold the bonding wire in place.

Waste of time? What is, bonding? This boat has a rather well-designed and installed bonding system (put in by the PO) which has been thoroughly inspected by surveyors and marine electricians. I understand the pro's and con's of bonding and would probably not go to the effort and expense of putting a complete bonding system in personally, but I'm not yet ready to rip this one out. And yes, I'm aware that using a hose clamp to hold a wire to a fitting is probably not the ideal electrical connection, but I have verified good continuity of this connection.

I hadn't considered salt water seepage, but it seems a long shot at best. This isn't the only one on the boat exhibiting this behaviour, but it's certainly the worst. Anyone know an at-home test to chemically differentiate NaCl from ZnO or AlO or other miscellaneous residues this might be?

I'm headed down there tomorrow with my ammeter to see if I can identify any stray current sources. Tests with a half-cell show my zinc protection to be spot-on, but that probably wouldn't result in this type of action anyway AFAIK.
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Old 10-04-2009, 08:06   #7
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I'm sorry rhunton, my "waste of time" comment sounds harsh, now that I read it. What I meant was that IMHO bonding thru's is useless at best and detrimental at worst. As for the hose clamp, I just found the same thing on my stuffing box. It must be common if theres no grounding screw. Please let us know what you find out, as I've never seen anything like it. I know Zinc can leach out of bronze, basically leaving brass, but I believe the part must be submersed. Although I doubt it, could it be a brass valve on a bronze thru? Cant wait to see what you find, Chris
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Old 10-04-2009, 08:43   #8
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taste it. if it's salty it's probably a seeping thru the threads as mentioned previously. If it doesn't taste salty like salt crystals then it's corrosion. Don't swallow.
LoL
In the future you might think of brazing a threaded stub to the brass valve(s) for bonding a ring terminal/wire that can be sealed with silicon afterward. Just a thought.
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Old 10-04-2009, 09:45   #9
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Good suggestions all thanks. I'm a bit reluctant to taste mystery substances in my bilge, strangely enough. But I may have to. Rather than brazing on studs, I will probably just replace with NST thru hulls and proper seacocks. Just trying to figure out how urgent that project is as it's not quite time to haul for my next bottom job.
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Old 10-04-2009, 10:35   #10
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I also noticed it wasn't a proper seacock. When I looked at the blow up of your photo, it also appeared to me the thru hull and valve were of different color and I wonder if there might be some issue of dissimilar metals.

I had a wake up call when I was looking at boats. We were on a sea trial and the surveyor went to check the valve, only to have the thru-hull fracture all the way through. Later, (after a very quick haul out), we could see a great deal of pinkish corrosion inside the through hull. I never would have believed such a failure would occur if I hadn't seen it myself.
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Old 12-04-2009, 12:43   #11
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Progress of sorts...

Well, after spending the weekend crawling around with a voltmeter, I've learned some things, but not sure if any are useful.

As is, there was about -12.5MA of current at -.35V between the fitting and the bonding system (once i disconnected it). The ball valve is definitely a different color than the through hull, it's too soft to be stainless, and not magnetic. There's a PN25 marking on it which appears to be a european pressure standard. Some googling suggests that it might be nickle plated brass which seems to fit. They also show some available in a BSP thread which matches what Beneteau claimed for the through hull, which explains how they avoid the mismatched threading issues and get along without a real seacock.

Long story short, i disconnected the entire bonding system at the bus, and measured the potenials between each leg and the -12Vdc system which it had been tied to. Some legs showed more current than others, varying between 4-5ma to as much as 25ma. There was about 30ma of current between the entire bonding system and the 12vdc ground.

Even after I disconnected the bonding wire and cleaned up the through hull, the through hull continues to accumulate fuzz. Measurements between the through hull and the water with a silver:silver chloride half cell show -590MV which is about where it should be AFAIK.

So, the only thing i can come up with is that there must be some galvanic action between the ball valve and the through hull. But why it took 8 years to start being a problem is a mystery to me. I can't find any current in the water to explain things, and the galvanic isolators should protect from that anyway. I guess I'll haul the boat and replace the through hulls and valves.

Against my better judgement, I also tasted the fuzz. Definitely not salt. Nasty tasting stuff, a bit soapy too.

I'd welcome any insights anyone has. I'd hate to go through the expense of doing all this only to see the problem continue.
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Old 12-04-2009, 13:48   #12
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Is that through hull a factory installation?
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Old 12-04-2009, 19:10   #13
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I thought bronze was an alloy of copper and tin?
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Old 12-04-2009, 22:56   #14
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Quote:
Originally Posted by rhunton View Post
So, the only thing i can come up with is that there must be some galvanic action between the ball valve and the through hull. But why it took 8 years to start being a problem is a mystery to me. I can't find any current in the water to explain things, and the galvanic isolators should protect from that anyway. I guess I'll haul the boat and replace the through hulls and valves.

Against my better judgement, I also tasted the fuzz. Definitely not salt. Nasty tasting stuff, a bit soapy too.

I'd welcome any insights anyone has. I'd hate to go through the expense of doing all this only to see the problem continue.
I would agree that you should install a proper flanged thru hull if it's below the waterline.

One question! Is this near any batteries??? The "fuzz" looks something like sulfuric crystals. Battery acid (fumes) may have been at work here.

Or even some liquid soap may be building up (bilge cleaner?).
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Old 13-04-2009, 05:16   #15
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Yes it's a factory install (except for the bonding system).

No, it's nowhere near the batteries.

Fuzz built up overnight after a thorough cleaning with a wire brush. Don't know how that could be soap.
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