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Old 04-12-2022, 08:08   #1
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Check out this prop shaft anode

Morning All ... I have attached a few before and after pics of my screw on acorn shaft zinc. As you can see it's a ZPC-3 Camp zinc. It is 3 1/16" long and weighs 1.8 lbs. I previously changed it about 3 yrs ago. The wrench mangled this a bit when taking it off. I realize every marina/usage/boat is different but I would have though more corrosion would have occurred (ignoring the mangled-ness). Any commentary as too this one and could I have waited a little longer. They cost about $30 online. Thanks ... Dennis
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Old 04-12-2022, 08:11   #2
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Re: Check out this prop shaft anode

While that is an extreme example, anode depletion often does not occur uniformly.
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Old 04-12-2022, 08:20   #3
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Re: Check out this prop shaft anode

fstbttms ... thanks for the reply. I agree with your comment. Note that the wrench broke off the 'chuncks' when trying to get it loose. It then spun easily by hand. I figure the galvanic corrosion weakened the material hence the smaller broken off pieces ?
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Old 04-12-2022, 08:26   #4
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Re: Check out this prop shaft anode

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fstbttms ... thanks for the reply. I agree with your comment. Note that the wrench broke off the 'chuncks' when trying to get it loose. It then spun easily by hand. I figure the galvanic corrosion weakened the material hence the smaller broken off pieces ?


Well the anode material was undoubtedly weakened by corrosion, but I suspect it was electrolytic, not galvanic, corrosion.
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Old 04-12-2022, 08:32   #5
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Re: Check out this prop shaft anode

fstbttms ... very good. I stand corrected, thanks again ... Dennis
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Old 04-12-2022, 09:25   #6
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Re: Check out this prop shaft anode

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...could I have waited a little longer. ...
General "rule-of-thumb", with lots of caveats, is that anodes should be replaced when they have been reduced to half their original weight. Weight can be tough to tell visually, as you discovered the spent anode is quite porous as some material has wasted from the inside. But, you could take the old one (all the various pieces) and compare its weight with the new one to get a general idea.

The caveats to the weight basis for replacement are there are lots of physical conditions that might also warrant replacement before 50%. These come down to things like uneven wastage, poor contact, poor physical strength caused by wastage, etc.
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Old 04-12-2022, 09:33   #7
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Re: Check out this prop shaft anode

HeywoodJ ... good 'rule of thumb' advice ! tx
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Old 04-12-2022, 09:58   #8
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Re: Check out this prop shaft anode

I've never had this problem....I change mine when the original disappears on it's own, without my help to take it off
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Old 04-12-2022, 21:51   #9
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Re: Check out this prop shaft anode

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Well the anode material was undoubtedly weakened by corrosion, but I suspect it was electrolytic, not galvanic, corrosion.
Did you take into consideration that the anode was 3yrs. old ?
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Old 05-12-2022, 09:00   #10
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Re: Check out this prop shaft anode

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Did you take into consideration that the anode was 3yrs. old ?
I took the OP's question to be about how the anode is depleted primarily on one side only. Not sure what the age of the anode has to do with it.
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Old 05-12-2022, 09:37   #11
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Re: Check out this prop shaft anode

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I took the OP's question to be about how the anode is depleted primarily on one side only. Not sure what the age of the anode has to do with it.
You thought it was electrolytic rather than galvanic. If it was electrolytic there'd be nothing left.
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Old 05-12-2022, 09:39   #12
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Re: Check out this prop shaft anode

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You thought it was electrolytic rather than galvanic. If it was electrolytic there'd be nothing left.
You're assuming that you know when the issue started. There is no evidence that if it is electrolytic corrosion, that it has been affecting the anode for three years.
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Old 05-12-2022, 09:53   #13
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Re: Check out this prop shaft anode

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You're assuming that you know when the issue started. There is no evidence that if it is electrolytic corrosion, that it has been affecting the anode for three years.
Electrolytic corrosion can be evident within hours. I've seen it eat a 1.5" shaft in two days. I think you are making a bigger assumption than I.
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Old 05-12-2022, 09:57   #14
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Re: Check out this prop shaft anode

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I Electrolytic corrosion can be evident within hours. I've seen it eat a 1.5" shaft in two days. I think you are making a bigger assumption than I.
Yes, I've seen rapid damage occur from stray current as well. I've also seen anodes be relatively untouched while the prop or shaft are destroyed. But the fact that it can occur rapidly doesn't mean this anode's condition is not evidence of it.

In all seriousness, what do you believe is the cause of this lopsided anode depletion?
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Old 05-12-2022, 10:02   #15
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Re: Check out this prop shaft anode

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Yes, I've seen rapid damage occur from stray current as well. I've also seen anodes be relatively untouched while the prop or shaft are destroyed. But the fact that it can occur rapidly doesn't mean this anode's condition is not evidence of it.

In all seriousness, what do you believe is the cause of this lopsided anode depletion?

I'd suspect metallurgical contamination of the anode given that there was no mention of shaft or propeller corrosion.
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