I have done the fat cat tour. Its a great time, but as far as I know you can't charter his boat and he doesn't give lessons.
Check out this website for up to date info on Playa Del Carmen and surrounding area.
Playa del Carmen, Mexico's Virtual Guide Book : Playa.Info The forum section of the website has been down since this afternoon, but I am sure it will be up again soon.
PDC is a great vacation spot. I have been there at least 15 times, so if you have any questions feel free to ask or post the question at the website.