Hi: There's just something about 3 motors in a PT boat... Gotta have them. I've built a scratch built British Vosper MTB, at 1/14 scale. It's 60 inches long and powerd by three 18vdc drill motors. Each motor turns direct-drive a 1 3/4" 3 bladed prop. The motors are controlled through Proboat ESCs. Other PT boat builders have had issues with not enough rudder authority sticking with scale sized units. I made mine a little bigger anticipating that problem. While only running the two motors in the Dumas PT works fine, there might weight penalties adding a 3d motor, esc and battery. But then, this isn't a raceboat. My boat will be powered by 3, 10 cell 4000mAh NiMH packs.

Good luck with your boat.

Mike