First I agree with what has been said. Having a smaller 18" pusher work tug, they have high superstructures so catch a LOT of wind. Going sideways or backward at full throttle is no fun. The brass Dumas gears sets are VERY noisey...nylon-belts/pulleys is better. There are some good Graupner or Pittman servo motors that might work. You might also look at the Dumas-Pittman (#2004) 5000 RPM motors for straight drives and adjust the props accordingly and they are quiet.

Dave...RCTUGGER