An ablative paint is designed to protect the hull bottom from marine growth. As the boat moves through the water during a long period of time, the ablative paint wears out. What most guys do is to paint the hull with a different color of ablative paint. For instance, if the present color is blue, the guys would paint over it with another color like green. When traces of blue start to show up on the hull after a period of time, then they know that it's time to repaint the bottom again. If it still looks good and there are no traces of a primer coat or the hull's gel coat, I would go ahead and just put her in the water. I wouldn't use a power washer on it because the power cleaning will remove it. Just scrape off any small marine growth with a plastic putty knife in any areas that you can reach.
Joe
I just purchased a 1974 O'Day 25. The lower hull, and rudder, has a powder like coating over the paint that that leaves a light dry powder residue on your hands, rags, etc. It appears to have been applied by a roller(?)What is it? Can I, or should I, remove it? How should it be removed? 
