Hooty,
A sleek airplane with that engine would be able to break 100 mph easily. So, I would suggest that you appraoch your problem from the viewpoint of how to keep a sleek 100mph airplane planing/skipping on the surface of the water rather than how to get a boat to go faster. The problem with most boats is that all their weight is in the back. This is a condition that we airplane-minded people call tail-heavy. This is an unstable condition for an airplane. Drop a playing card from shoulder height and it will tumble end over end to the ground. Put enough paper-clips on one side and it will become a stable glider. I know everyone here has seen video of those super-fast speed boats that hit too big a wave, nose up into the air and do backward somersaults like that playing card did before you added the paper-clips. They both do backflips for the same reason. Do a google search for "flying boat foamy" to get some ideas how to design one for your .61fx. I havn't seen anyone build a glow powered one yet. They all seem to be small electrics. Check out the Ezone forums there must bee some good threads there on flying boats. Build and learn how to fly one of these without telling your "boating friends" then show them your new boat. Fly it off the surface of the water and pretend you didn't know it could fly. It'll blow their minds!