A scraper like Tommy,s works pretty well but you will get some gouges. You will need a powerful orbital sander and 60 and 80 grit to get a smooth job. You will take off some gel coat so I would recommend putting on the recommended coats of a good barrier epoxy.
I would allow lots of time, took me about 4 weeks to do a 30 footer with about 20 years of bottom paint on it. I found I could only work at it about 2 hours at a time.