For VC-17, depends on what's on there now!
A previous respondent recommended VC-17. I do to with one or two reservations. If there is not VC on the boat already, the bottom prep can be quite tedious. I know, because I've done it twice (with my first two boats).VC-17 requires a hard base. VC-Tar, Interlux barrier coats, or one of the hard racing bottom paints seem to be OK (read the instructions from the VC-17 people) If you have a soft, ablative bottom paint on there now, you will need to remove ALL of it, down to gelcoat or to a previous hard bottom. This usually required sanding to get rid of all of the soft crap. Once the bottom is sanded (and since you have spent so much effort in removing all of the previous bottom paint, you might as well fair the hull and the keel now), you should probably apply a barrier coat (to prevent blisters that might now form because you just damaged whatever barrier coat was already on the bottom).From here (and for all future years), just paint on the VC-17 and forget it. Prep for next year involvs washing the bottom with soap and water, rinsing with soap (and if you are feeling ambitious, acetone), and applying one or two coats of fresh VC-17. It dries in a few minutes (use a SMALL (5" or so) foam roller (the West System epoxy roller is excellent), and cover the top of the paint tray with aluminum foil to prevent too rapid evaporation of the solvent.For a C-27, you should be able to paint the bottom of your boat with two coats and use no more than 3 - 4 cans (0.8 qt /can)