Since I just finished reading Nigel Calder's chapter on corrosion, I'll take a crack at this.
Just speculating here, but do you have any other anodic metals that could have been acting as anodes instead of your zincs before? Ex, if you had the prop painted with zinc chromate, I believe that could act as the anodic zinc first. If that is used up now, it could explain why galvanic corrosion moved on to your prop nut + shaft zincs. Next thing I would worry about is stray current corrosion. I think of stray current corrosion as like galvanic corrosion on steroids. A weak DC current in the water can waste zincs hundreds of times faster than galvanic corrosion. Stray current corrosion on a mooring would have to be coming from your boat. It can be caused by things like a partial short in your bilge water (ex, bad bilge pump). You can test for it with a silver/silver chloride half cell (costs about $120) using the procedure in Nigel's book. -Patrick 1984 C&C LF38 Seattle, WA On Thu, Dec 24, 2015 at 9:00 AM, <cnc-list-requ...@cnc-list.com> wrote: > ---------- Forwarded message ---------- > From: David Knecht <davidakne...@gmail.com> > To: CnC CnC discussion list <CnC-List@cnc-list.com> > Cc: > Date: Thu, 24 Dec 2015 11:47:25 -0500 > Subject: Stus-List Zinc decay > When my boat was pulled from the water this year I was surprised to find > that the Max-prop zinc was gone, one of the shaft zincs was gone and the > other was nearly gone. I have had this configuration in past years and > every other year at the end of the season I could barely justify replacing > them because there was so little metal decay. I know of nothing I did > differently this year. I am on a mooring so rarely plugged into shore > power. What would cause a dramatic increase in zinc decay? Thanks and > Happy Holidays to all! Dave > > Aries > 1990 C&C 34+ > New London, CT >
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