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04-12-2022, 07:08
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#1
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Registered User
Join Date: Dec 2015
Location: North Carolina, US
Boat: Catalina 350
Posts: 76
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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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04-12-2022, 07:11
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#2
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Hull Diver
Join Date: Oct 2006
Location: Under a boat, in a marina, in the San Francisco Bay
Posts: 5,427
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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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04-12-2022, 07:20
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#3
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Registered User
Join Date: Dec 2015
Location: North Carolina, US
Boat: Catalina 350
Posts: 76
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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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04-12-2022, 07:26
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#4
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Hull Diver
Join Date: Oct 2006
Location: Under a boat, in a marina, in the San Francisco Bay
Posts: 5,427
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Re: Check out this prop shaft anode
Quote:
Originally Posted by kingofcary
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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Well the anode material was undoubtedly weakened by corrosion, but I suspect it was electrolytic, not galvanic, corrosion.
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04-12-2022, 07:32
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#5
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Registered User
Join Date: Dec 2015
Location: North Carolina, US
Boat: Catalina 350
Posts: 76
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Re: Check out this prop shaft anode
fstbttms ... very good. I stand corrected, thanks again ... Dennis
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04-12-2022, 08:25
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#6
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Registered User
Join Date: Oct 2021
Posts: 589
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Re: Check out this prop shaft anode
Quote:
Originally Posted by kingofcary
...could I have waited a little longer. ...
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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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04-12-2022, 08:33
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#7
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Registered User
Join Date: Dec 2015
Location: North Carolina, US
Boat: Catalina 350
Posts: 76
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Re: Check out this prop shaft anode
HeywoodJ ... good 'rule of thumb' advice ! tx
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04-12-2022, 08:58
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#8
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Marine Service Provider
Join Date: Jan 2019
Boat: Beneteau 432, C&C Landfall 42, Roberts Offshore 38
Posts: 6,253
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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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04-12-2022, 20:51
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#9
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Marine Service Provider
Join Date: Nov 2008
Location: Port Credit, Ontario or Bahamas
Boat: Benford 38 Fantail Cruiser
Posts: 7,047
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Re: Check out this prop shaft anode
Quote:
Originally Posted by fstbttms
Well the anode material was undoubtedly weakened by corrosion, but I suspect it was electrolytic, not galvanic, corrosion.
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Did you take into consideration that the anode was 3yrs. old ?
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If you're not laughing, you're not doin' it right.
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05-12-2022, 08:00
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#10
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Hull Diver
Join Date: Oct 2006
Location: Under a boat, in a marina, in the San Francisco Bay
Posts: 5,427
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Re: Check out this prop shaft anode
Quote:
Originally Posted by boatpoker
Did you take into consideration that the anode was 3yrs. old ?
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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.
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05-12-2022, 08:37
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#11
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Marine Service Provider
Join Date: Nov 2008
Location: Port Credit, Ontario or Bahamas
Boat: Benford 38 Fantail Cruiser
Posts: 7,047
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Re: Check out this prop shaft anode
Quote:
Originally Posted by fstbttms
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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You thought it was electrolytic rather than galvanic. If it was electrolytic there'd be nothing left.
__________________
If you're not laughing, you're not doin' it right.
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05-12-2022, 08:39
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#12
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Hull Diver
Join Date: Oct 2006
Location: Under a boat, in a marina, in the San Francisco Bay
Posts: 5,427
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Re: Check out this prop shaft anode
Quote:
Originally Posted by boatpoker
You thought it was electrolytic rather than galvanic. If it was electrolytic there'd be nothing left.
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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.
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05-12-2022, 08:53
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#13
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Marine Service Provider
Join Date: Nov 2008
Location: Port Credit, Ontario or Bahamas
Boat: Benford 38 Fantail Cruiser
Posts: 7,047
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Re: Check out this prop shaft anode
Quote:
Originally Posted by fstbttms
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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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.
__________________
If you're not laughing, you're not doin' it right.
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05-12-2022, 08:57
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#14
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Hull Diver
Join Date: Oct 2006
Location: Under a boat, in a marina, in the San Francisco Bay
Posts: 5,427
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Re: Check out this prop shaft anode
Quote:
Originally Posted by boatpoker
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.
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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?
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05-12-2022, 09:02
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#15
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Marine Service Provider
Join Date: Nov 2008
Location: Port Credit, Ontario or Bahamas
Boat: Benford 38 Fantail Cruiser
Posts: 7,047
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Re: Check out this prop shaft anode
Quote:
Originally Posted by fstbttms
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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I'd suspect metallurgical contamination of the anode given that there was no mention of shaft or propeller corrosion.
__________________
If you're not laughing, you're not doin' it right.
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