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  #11  
Old 01-24-2012
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Quote:
Originally Posted by L124C View Post
Going through a prop zinc about every 1.5 years. I've tested the water for current and don't find any.
If this 'shaft log' isnt *electrically bonded* to an external or 'wetted' anode ... sorry but 'any' zinc within the composition of this assembly will be the 'anode'.

ALL metals that come in contact with seawater, etc. should either have an anode attached or be 'bonded' to an anode. Since the 'packing' in the shaft log is electrically isolating this assembly from the 'shaft' zinc .... the assembly is 'on its own' w/r to 'electrolysis', etc.
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Old 01-24-2012
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Originally Posted by L124C View Post
Wow!!! It could be THAT brittle?
I assume "punky" is a dull, (not sharp metalic) report? (PUNK vs. PINK)
If so...it might sound like PUNK, PUNK, SPLASH!
Absolutely!!! When replacing my strut, the part containing the cutlass bearing literally crumbled in my hand when squeezed. I was very lucky this did not come apart on the way to the haul out.....
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Old 01-24-2012
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Absolutely!!! When replacing my strut, the part containing the cutlass bearing literally crumbled in my hand when squeezed. I was very lucky this did not come apart on the way to the haul out.....
Pink= VERY BAD!!!!
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Old 01-24-2012
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Originally Posted by RichH View Post
If this 'shaft log' isnt *electrically bonded* to an external or 'wetted' anode ... sorry but 'any' zinc within the composition of this assembly will be the 'anode'.

ALL metals that come in contact with seawater, etc. should either have an anode attached or be 'bonded' to an anode. Since the 'packing' in the shaft log is electrically isolating this assembly from the 'shaft' zinc .... the assembly is 'on its own' w/r to 'electrolysis', etc.
The shaft packing does not completely "isolate" the packing gland, especially in an electrolyte. If you add a graphite based packing you've now added one of the most noble materials you can and every thing becomes anodic to the graphite impregnated packing. A stuffing box is pretty well protected by the shaft zinc and this can easily be confirmed with a reference cell. If bonded to the engine you'll see a slight change in the reading but not a whole hell of a lot, and it should not be enough to matter.. I would take a brass brush to it and see if it scrapes off. I can't recall a stuffing box displaying that kind of dezincification, if in fact that is what it is. What brand of boat is this on..?

Dezincification can be bad..






And why graphite impregnated packing can be bad with a bronze shaft..
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Last edited by Maine Sail; 01-24-2012 at 07:38 PM.
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Old 01-24-2012
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If the front edge of the stuffing box is not immersed in water, how would de-zincification occur without an electrolyte? Could it be from the water that leaks through? If so, you would also expect the de-zincification to occur on the INSIDE of the stuffing box, where you can't see it unless you take it apart. Greasing the outside might insulate the visible metal (maybe captflood is on to something here) but that seems like a temporary cosmetic fix: you still have to wonder about what is going on inside.

If you want to sleep at night, take it apart next time you haul out. You might consider replacing it with a PYI dripless shaft seal (no bronze) and worry about something else.
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Old 01-24-2012
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If you connect some wires in the right spots you can charge your battery But i would fix it first of all.....happy sails!!!
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Old 01-25-2012
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Originally Posted by Maine Sail View Post
What brand of boat is this on..?
1970 Yankee 30 with a Yanmar refit sitting midships (if that possibly matters). The zinc and prop are probably no more than three feet from the stuffing box. I'll clean the stuffing box today and repost the results. As always...thanks for the informative posts and pics!

Last edited by L124C; 01-25-2012 at 12:14 PM.
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Old 01-26-2012
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Cleaned it with brush. Most of the green patina stayed and so did the pink in the front (not enough change to post a picture). The nuts are Bronze color, but that front edge is still pink!

Last edited by L124C; 01-26-2012 at 01:36 AM.
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Old 01-26-2012
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Clean it with scotch brite or some abrasive to see if it is only on the surface
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Old 01-26-2012
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Quote:
Originally Posted by L124C View Post
Cleaned it with brush. Most of the green patina stayed and so did the pink in the front (not enough change to post a picture). The nuts are Bronze color, but that front edge is still pink!
Yah, no...it's underwater. You can do the Thunderdome thing and roll the wheel and take your chances. The pink coloring is caused by galvanic corrosion / electrolysis which causes loss of zinc in the bronze. The pink color is copper. The problem is not repairable as the metal has morphed. It should be replaced.
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