The beltdrive system for the 700 motors at the bottom of the page on this link looks like it would have a ton of power for a boat application. I'm considering three of those for a 16th scale pt project, I have two 540 motors mounted in my Lindberg pt boat on the smaller beltdrive listed there. It's capable of close to twenty miles an hour with 1.5 inch three blade 35 degree brass props. Those beltdrives are wisper quiet and will really "tourque up" your motor as opposed to direct drive.
http://www.hobby-lobby.com/drives.htm
The beltdrive system for the 700 motors at the bottom of the page on this link looks like it would have a ton of power for a boat application. I'm considering three of those for a 16th scale pt project, I have two 540 motors mounted in my Lindberg pt boat on the smaller beltdrive listed there. It's capable of close to twenty miles an hour with 1.5 inch three blade 35 degree brass props. Those beltdrives are wisper quiet and will really "tourque up" your motor as opposed to direct drive.
http://www.hobby-lobby.com/drives.htm