Anodes, Questions

I recently put my boat on the hard to check/replace anodes. All the anodes were similarly reduced which is probably a good thing? My boat is mostly bonded except for the rudder and rudder shaft (hydraulic steering has nylon tubing). I have not had the boat for much more than a year and this is the first time I have replaced zincs. When I was rehabilitating the boat one of the things I did was clean up the rudder. The rudder had a typical rudder zinc and when I removed it I noticed that the underlying stainless was very corroded. The rest of the rudder blade had a lot of shallow divots, looked like some kind of corrosion to me. I filled and faired the blade with epoxy and painted it and then bottom paint. While working on the rudder I noticed that the shaft was nonmagnetic but the blade was. They are welded together. The shaft showed no signs of corrosion. I put a shaft zinc on the rudder shaft. The rudder shaft sits in a socket in the steel keel shoe and the keel has a zinc on it but as far as I know there is no connection to the bonding system. The rudder currently shows many blisters in the paint which indicate to me that the problem is ongoing.

The only other thing I noticed is hard crusty greenish deposits on the bronze rudder. I could scrape it off but it took a while. What is this?

I have read so many posts about bonding etc that my head spins. My bonding system goes to a hull plate but I also have zincs on copper keel cooler( bonded), prop shaft (bonded), rudder shaft (not bonded), keel (not bonded).

I'm a little confuse by your post. You say the rudder is stainless but then say it's bronze.

If the rudder shaft is non-magnetic stainless, it is probably 316 which is a good underwater alloy. If the rudder is stainless but magnetic, it is likely 304 which is not very good under salt water. If they are welded together then they are bonded electrically for sure, and the 304 would lose to the 316. But good zincs really should keep either from corroding very fast.

DDW said:

I'm a little confuse by your post. You say the rudder is stainless but then say it's bronze.

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Click to expand...

Sorry in the second parafraph I meant bronze prop. The forum is not letting me edit right now.