As Edward said WAx.
2 comments.
Polish it until it shines (really really shines ) the micro scratches give the barnacles something to hold onto so the better the polish the less grip they can get.
Wax or lanacoat will last for part of the season (6 months good 3 more ok and the last 12 a little better than the first 12 on a bare prop. = Not a lasting non stick, but better than paint. Lanacoat can be done without the heat = less chance of an opps.
Recoating under water is +/- = Not sure if it is worth the effort, but can be done with the lanacoat in a plastic sandwich bag, pushed the stuff all over the prop blade one at a time but not sure this helps that much maybe ok for 1 to 2 months?
I tried the bag = ok if you leave it a long long time in one spot but a pain in the a$# if you move and then what do you do with the bag it smells allot? and some stuff sneaks through any way.
Last three tips
1.) kevlar gloves! The kind they sell for knife work on fish.
2.) tie a long line to the scraper and tie off one end to a boomkin stay just in case you drop it. saves the bad words.
3.) Hydrogen peroxide for the cuts you get (Put it on as you are getting out of the water = ASAP)