It's got a few kinks in the it but its a huge loop that'll launch you across the map if you can stay on it long enough. An airboat is provided with thrusters set at the highest setting. Press 0 (kp_ins) on the Keypad to fire the thrusters.
The map "Waterworld.bsp" is needed so heres the link to download. I did not make this map: http://files.filefront.com/waterworldbsp/;6525104;;/fileinfo.html
This saved game also requires GMOW (GMOD on wheels) Models:
If you get lost in this map (because of its shear size and simplicity at most parts) follow the buoys back to the island or just reload the game.