Shawn; here's a video you might enjoy... if you want to build one for yourself watch all the vids from 1 through 10 to see how it was built. A red neck jet boat.
http://www.youtube.com/watch?v=rG8AB807f5I
Basically this is trash pump drive.
On a more serious notion I believe you actually need this
http://www.youtube.com/watch?v=iZXgDX8Wrw8
http://www.youtube.com/watch?feature...xfglrow6A&NR=1
Shawn; it just so happens that I will GIVE YOU a gas powered weed eater (industrial strength with broken blade holder on end of shaft, but it works all good otherwise) if you will make one of these!
http://www.youtube.com/watch?v=8E3Y-...eature=related
This would work awesome in the river; easy to tilt when approach rocks and I'll bet it would push a 14 foot jon boat with ease.
Heck; I would have thrown in the jon boat but it got ripped off from my son's yard several weeks ago... it was Sears "ted Williams" vintage early 70's. Think a couple meth heads stole it for the metal.