You may want to have a look at this [link=http://www2.towerhobbies.com/cgi-bin/WTI0001P?&I=LXE411&P=V]running gear[/link] setup. It's for a Mr Darby tug and has unreal power. It's for two motors and has as I recall a 7:1 reduction gear setup. Not a real speed demon but has a ton of power. I use to pull the better half around the marina on an air mattress all day long with a 12volt bike battery and the Mr Darby I have was about 55 lbs when ready to sail.