RE: jet drive boat
I'd go with two 29mm drives in a boat that size. And a shallow V hull is preferred with jet drive propulsion. You could use an electronic esc such as a Traxxas and an [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXMGM3&P=FR]HPI Reverse Mixer[/link] to control the reverse bucket with a 2 channel radio. Just hold the throttle in reverse for 3 seconds and it will flip a servo the other direction. A Traxxas XL5 will power two Speed 500's in parallel.