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Old 07-18-2017, 08:12 PM   #1
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Galvanic Corrosion?

Need a little help with the below.
Having an issue with some growth on the Shaft Logs behind the stuffing boxes, Port and Stbd, inside the vessel. For some reason we are getting this buildup which is a very fine, white powdery crystal and forms on the surface. Like what you get on battery terminals but a lot finer.
I am sure it is some type of galvanic corrosion. The galvanic isolators are on and showing green lights.
Is there a simple way to test this with a multi-meter?
What if I put an anode strap on there?
Any ideas would help.
Also Has anyone seen this type of shower drain. Is it a small pump inside?
Cheers.
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Old 07-18-2017, 08:20 PM   #2
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I would say that it looks like a standard gravity drain and if there is any pump it should be at the end of the green hose. Where is the through hull for this one?

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Old 07-18-2017, 08:28 PM   #3
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Could it be crystallized salt?
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Old 07-18-2017, 08:39 PM   #4
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Doesn't look like galvanic corrosion. But if you're concerned about it, by a reference anode from boatzincs.com or some other source and put your mind at ease.

Corrosion Reference Electrode Product Specifications

I just tested my boat with one of these and it's nice to know the readings are in the safe range.
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Old 07-18-2017, 09:37 PM   #5
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Quote:
Originally Posted by FlyWright View Post
Could it be crystallized salt?
That would be my guess. Put it to the taste test.
If packing gland is dripping proscribed amount, it will be spun into a fine spray when running and the shaft log might be within the spray zone. You could cover the gland with a piece of plastic from a milk jug.
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Old 07-18-2017, 11:22 PM   #6
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More likely it is salt crystals left from seawater weeping past caulking or being flung off the spinning shaft at the stuffing box.
That mist can travel and cause what you are seeing. AND. cause serious rusting of any steel components nearby, gear box, engine, mounts, etc.

Can,t say for sure as photo not terrific and diagnosing over internet not good either.

Adjust the packing to the required minimum drip. Cover the box where the shaft enters with an old fender cut so it contains the spray and collect the water getting it to drip into the bilge rather than flung into the air as a mist. Use a clamp to secure the fender piece.

The silver/ silver chloride half cells can be bought from your Chandler or from
Boatzincs.com
Get instructions about how to use it properly.
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Old 07-19-2017, 12:09 AM   #7
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Thanks for posting this one - I just had to replace two half-shafts on Content, and I don't know whether my boat was the culprit, or another. They'd been completely compromised in only 12 months. I do know that in the two weeks between two haul-outs last month, significant damage was done to my brand new zincs, in the marina I'd left her in for the first time last winter.

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Old 07-19-2017, 10:45 AM   #8
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Quote:
Originally Posted by Lou_tribal View Post
I would say that it looks like a standard gravity drain and if there is any pump it should be at the end of the green hose. Where is the through hull for this one?

L.
Yes will follow that when I get the boat back.
But I guess I thought it was some small pump as there is a wire attached that goes back to the vanity. See pics.
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