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Old 22-11-2017, 05:51   #1
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Hello, I've noticed some electrolysis happening on what I think is called the P bracket (please see picture).

Here are the points:

1. Installation is on a 2010 Jeanneau.
2. Tha anode is on the end of a folding prop
3. The shaft is stainless (no sail drive)
4. I've had propspeed on the prop since new
5. I've put red oxide as an undercoat and micron extra on the P bracket (and shaft)
6. The P bracket has a ground shield attached by the manufacture.
7. This year the anode has worn more than usual.

I haven't found red oxide and micron extra to be very good on this P bracket and shaft (lots of quick growth). Usually barnacles grow on it and I chip them and then antifoul off to clean it during the year.

The boat is currently out of the water and my plan is to put propspeed on it instead to see if growth slows. Any suggestions before the boat goes back in the water in a day or two I would look at trying (but don't think its a good idea to put an anode directly on the p bracket at this stage).

I wonder if red oxide could be a problem for electrolysis. The boat does not sit in a marina.

Any suggestions?

Thank in advance.
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Old 22-11-2017, 11:01   #2
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Re: Electrolysis

Propspeed won't stop growth at all, but it will make the strut easier to clean. I've had somewhat similar issues with the strut on my boat, and have tried both different types of antifouling and propspeed. The propspeed stayed on best, but needed cleaning. None of the antifoul paints stayed on well, but did inhibit growth while still in place.


Jim and Ann s/v Insatiable II , lying on the Clarence river in the vicinity of Ashby, doing boat chores.
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Old 22-11-2017, 11:13   #3
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Re: Electrolysis

Thanks Jim, but my question is really about the electrolysis happening. The reason for mentioning the antifoul was only in case the red oxide had anything to do with it.
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Old 26-11-2017, 04:53   #4
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Re: Electrolysis

Don't know much about the red oxide.... But what is that bracket made of - the micron extra contains copper, which accelerates corrosion of many metals.

Btw, it's not "electrolysis" as such, but "galvanic corrosion"
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Old 26-11-2017, 16:31   #5
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Re: Electrolysis

Or, maybe it's just not a smooth casting. Ours isn't smooth either, but it doesn't get worse from year to year. If yours has, then something's going on.

Who scorns the calm has forgotten the storm.
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Old 16-12-2017, 16:10   #6
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Re: Electrolysis

Thanks for your replies. Its some sort of bronze alloy I'm guessing. I don't think its a casting issue as you can see a colour change.
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Old 16-12-2017, 20:00   #7
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Re: Electrolysis

The zinc on the prop or on the shaft can not protect the prop strut. It is electrically insulated from the shaft by the rubber lining of the cutlass bearing.

You fix the problem by adding a zinc to the strut--something Jeanneau should have known to do in the first place! They used to know how to build a boat that would last...

Oh, one more thing... the electrolysis is the reason you have so much trouble with your paint on this strut.
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Old 16-12-2017, 20:22   #8
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Re: Electrolysis

Assuming that Jeaneau's practice is to electrically bond all underwater metal with ground wires, check that the ground wire inside the boat attached to the P-bracket is tight and clean. If you measure the resistance between the p-strut and the prop-shaft, it should be very low.

Whenever you are see signs of galvanic corrosion check all grounding wires. Also check that the shaft is grounded (might not be if there's a flex coupling). If necessary, install a shaft brush.

But the red is probably not a problem. It could just be a minor flaw in the casting. Certainly monitor it to see if it gets worse. As long as the zincs don't disappear completely and the metal is all connected, they are doing their job. The faster erosion could be due to a "hot" boat in a nearby slip.
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Old 16-12-2017, 20:27   #9
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Re: Electrolysis

forget 'red oxide' just clean that strut good with 80grit and anti foul it with the Micron then make sure the bolts holding it inside hull are attached to the boats bonding system Plus put a torpedo style zinc on the prop shaft ahead of the strut.

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