I treated the propeller and stern thruster with Jotum Primer Antifouling. From the middle of the season, the effect of the stern thruster decreased significantly. When the boat was craned in November, the cause was quickly found. The stern thruster propeller was completely covered with barnacles. The stern propeller was clearly infested with barnacles. For comparison, the underwater hull was treated with Hempel and had almost no barnacles. I'll sand off the antifouling and try something else. The processing was good, but does nothing. I cannot recommend the Jotum system. The sailing area is the Baltic Sea and the Elbe.
This propeller antifouling worked well. Apart from a few small spots, the propeller looks pretty good. It had a lot of growth before. The boat is moored in the middle of the Schlei. The pictures from last year and now say it all.