Propspeed was mentioned, post 39. Our friends have used it over bare aluminum going on 14 years now. Reporting each year. Drives look perfect.
Your zincs look wasted. We love the split zincs, easy to change, and we are applying propspeed to our drives in 5 days.
I am surprised no-one here mentioned "propspeed". I haven't tried it yet, but I was told that that's the antifouling that is good for using on props and other metal parts, such as the saildrive.
If I remember correctly way back the OP is wanting to use Coppercoat on his hull to reduce/eliminate the very expensive haulouts in his area. Coppercoat claims a 10 year life. Propspeed will not last near that long. It is more a one season, maybe two coating.
Had the diver change the zinc today. It was completely busted:
After I watched him do it (he was free-diving) I am confident I can do it myself next time. If you have doubts, just give it a try, grab the number 6 hex wrench and free dive as many times as needed, doing one small thing at a time. just be careful not to scratch yourself against the barnacles