International Prop paint works for me..
I tried various option over the years, now on my 29,5 ; Now I use the special formulated Primer+hard Antifouling paint by International (it is white coloured) for propellers and S-drives .It works quit good if correctly applied,incl special primer, but still Iess than the soft antifouling paint on the body.While the hull paint is effective for about 2 years ( I keep my boat in the water year around, in East Mediteranean , warm and salty water)the propeller paint is effective for about one to one and a half year . Anyway I dive once a month or two , to freshen the paint around water-line, rudder , shaft and propeller , by lightly going over with a sponge.It is longer than I got for the propeller with any other alternative I tried.