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Old 17-07-2008, 12:27   #1
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Bizarre calcification issue on props and shafts

Hello everyone,

I am a diver in san diego and I have a customer who has a bizarre calcification issue under his boat. When I first picked up the account, I figured that it was residue of some previous electrical issue. I cleaned the vessel and polished the shafts. The following service, the shafts and props were coated with the same white chalky substance. In the 8 years that I have been diving, I have never see such rapid calcification before. I figured that maybe the zincs were possibly dead. I polished the contacts and slapped new anodes on the zincs during the last service. I came back to the vessel two days ago for the next service and the calcification problem persisted (Im sorry I keep calling it "calcification," it might not even be calcium). I checked out the zincs, and they were not even burning. In fact, the zincs had growth! Thats right, the zincs looked as though if I had just put them on and there was some stuff growing on them.

I was wondering if anyone might have an idea as to what might be going on under this boat. It is a 32' luhrs with two 1 1/4" shafts
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Old 17-07-2008, 12:36   #2
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When you say "calcification", does that mean it is securely adhered to the metal, as tightly as, say, worm tubes or barnacle bases? Or does it wipe off relatively easily. Is it uniform in thickness or found in patches? Any chance of a photo? Also, what part of the Bay is the boat located?
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Old 17-07-2008, 13:40   #3
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Securely adhered to the metal. Sandpaper is required to remove it and it cakes off when removed. Its not like a film, but more like a coating of hard white chalky stuff. It does not wipe off relatively easy. Uniform in thickness, not really patchy, but it pretty much covers the entire shafts and props. The boat is located in Mission Bay, Quivera Basin. As far as a photo, someone I used to work with has a camera. Ill see if I can borrow his to take some pictures of it. In the meantime, do you know what it might be? I told him that the issue may very well be electrical, and we might dispatch someone to read his ampage. Other than that, I have no idea.
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Old 17-07-2008, 14:02   #4
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What makes you think it is calcium? Could be another metal plating on the shaft and prop. Is there any steel or aluminum boats close by? I've seen outdrive completely dissolved by poor grounding of metal boats. Tha aluminum ended out plting out on other boats running gear. Owner should have electric connection checked for proper ground current.
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Old 17-07-2008, 14:15   #5
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I'm thinking what speciald above is...

It's on the receiving end of an electrolysis problem. Somewhere... not too far away... somebody is on the losing end.
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Old 17-07-2008, 14:26   #6
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I'm still not leaping to the electrolytic side yet. Do any of the nearby boats have a similar coating? If it is possible to take some off with one of the 3M scrub pads, put some vinegar on it and see if it foams. That will answer the calcium carbonate question. If it doesn't foam, get me a sample of it - I'm in San Diego and can possibly get an analysis. Send me a private message for contact info.
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Old 17-07-2008, 20:15   #7
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speciald, youre right, it might not be calcium. I am not certain what it is

hm. I can definitely scrape off some of that material to see if it fizzes with vinegar or some other weak acid solution. Ill probably head back there over the weekend and take a sample. Roy M, thanks for the assistance, I will keep you updated via pm whether or not its caco3.
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Old 17-07-2008, 21:45   #8
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I see this all the time (although maybe not as rapidly as the buildup you are experiencing) and my understanding is that the white scale is deposited as the zinc begins to deplete. The zinc gives up ions which are then deposited on the prop shaft. I don't even remember where I read this or if it is actually true.
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Old 17-07-2008, 22:03   #9
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Perhaps it is pertinent but the zincs on my wooden boat used to "calcify" if one of two things were happening. If I put too much zinc on the boat OR if I had a strong current in the boat from something such as a bilge pump wire eaten off and submerged in the bilge water.
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Old 18-07-2008, 09:12   #10
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I think aquabumdotnet said that the zincs appeared unaffected. If they were pitting and disintegrating I would be more likely to go with that possibility. At any rate, with a scraping sample it will be pretty easy to identify the material (I hope, since I really love mysteries).
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