I didn't use to paint the prop.
The method I use is a good considerable amount of vaseline applied every time the boats goes in the water.
The vaseline keeps the barnacles out, as it coats the saildrive with a thin greasy layer..I have up to 6 months barnacle free.
This year, we decided to paint the prop also with saildrive paint (no metals in the paint to avoid dissimilar metals corrosion), and applied vaseline.
Boat's coming out in 1 month for hull washing and cleaning..I will let you know. But after 3 months in the water, I dove and inspected and there were only 2 or 3 barnacles on it..
The vaseline also helps the ones that make it and attach come off easier without bringing the paint with them...that was the original idea with the vaseline, so they don't bring paint with them when pressure washing.
Prop before painting bellow.
Prop with painting AND vaseline bellow.