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Old 05-14-2019, 09:36 AM   #16
Bkay
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City: Reedville, VA
Vessel Name: Wingspan
Vessel Model: Aluminum Catamaran
Join Date: Aug 2018
Posts: 580
I usually hurt myself with a volt meter, so I'm not the best source. But in this case, it should be painless to start trouble shooting.

I'd start my looking at the resistance (ohm setting) and see if there is any electric connectivity between the shaft and the stern tube. If you have infinite resistance then there is no connection. It should be the same on both shafts. (note: Touch the probes to two different, unconnected pieces of metal to see what infinite resistance looks like. Touch them to each other to see what 0 resistance looks like.)

If there is good connectivity between the bronze stern tube and the shaft and both read similar, then checking for even wear in anodes is simply a matter of looking at them when you haul.

You may find no connectivity (infinite resistance). If there are any readings that are different from one side to another or if there is materially different wear in the anodes, I'd ask a smart electrician to assist with a survey. I have always seen those done in the water with a silver/silver chloride reference anode hung over the side and readings taking from inside the boat to determine the difference in potential. This is something that you are better off watching the first time.

With a haul out coming, I'd be satisfied with just confirming whether either or both sides have continuity. If they do, then your shaft anode is the protection for the stern tube. If everything looks and feels normal, then you are probably back to the question of how to clean up the verdigris. But if copper bottom paint is turning colors around the fittings, an anode is worn through, or one side has a difference in continuity, then it's time to talk to a smart guy.

Hope that helps. I usually just try to common sense these things out until I get frustrated then hand someone a bag of money to explain what the clues mean. Hopefully someone better educated than me will chime in.
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