None of the components requires support and they can be printed with low infill.
The gearwheels used have a shaft distance of 28mm, 18/38 teeth module 1.
If your wheels are different, just adapt the shaft distance in the SCAD file. The place is indicated.
The size of the gearwheels is not very important, as long as the smaller one fits in the opening of the housing
Before gently pushing the motor in place, the smaller gearwheel is pushed onto the motor shaft.
The larger gear wheel is mounted on a 35mm M3 shaft using two M3 nuts and a lock washer. The two crankshafts are screwed on at both sides and locked with a nut/bolt combination. Make sure they are in the same position.
When ready, the motor housing is mounted in the hull with four M3 bolts.
After taking of his shoes, MakerBot Man is glued to his seat with a two component epoxy adhesive. The crank shafts are snapped into his hands and the seat is bonded to the hull at a position where the body follows the rotation of the crank shafts easily. If MakerBot Man does not pull the oars under water, but pushes them, you can swap the motor unit 180 degrees or reverse the wires of the power supply.
Usually, rowing boats don’t have a rudder. However, if you have a small pond, it would be nice to row in circles. That’s why an invisible underwater rudder can be attached to the boat. Use the 3mm hole to attach your own rudder design.