I have an Ericson 27 with a similar size motor built by Mars. To give you an idea of performance, at 20 amps I get 4 knots of boat speed. I have motored in calm conditions for 7 hrs at 4 knots and used half of my capacity - two 100 amp hr battery banks. On your 33 you should be able to add another bank pretty easily. My system is set up so I can motor on one bank while charging the other using an external generator (Honda 2000). I have never done that but there are others using Honda 2000's to extend their range. Check out the Yahoo Electric Boat Group to find out what other's are doing. It is a growing industry with more people making the switch all the time. You're going to like the relative simplicity, quiet, odor free, immediate power motoring you get with Electric propulsion :-).