my Dauntless is currently running two Mabuchi 550s and two 6V gel cells wired in series to make 12 volts. I have cooling coils installed but they aren't hooked up because the motors stay cool on their own. It is a direct drive setup. The boat's 1 3/4" 3-blade brass props are configured for counter-rotation. I use a Novak EVX for electronic speed control, but don't like the whiny noise the EVX makes at slow speeds... not very scale[]. These motors don't draw too much power yet move the boat along nicely. I used to have just a couple microswitches and a servo for full forward or full reverse and it was still fun and easy to drive, if saving $$$ is a goal of yours.

I tried Dumas 2" props and the boat was a bit faster but the motors nearly overheated after about 15 minutes. In this setup I should have probably went ahead and got the water cooling finished.