Motor specs for my solar electric cat

The 16 meter by 7 meter solar electric catamaran that I am planning will have two 7500 watt electric drives. In order to find the best electric motor, I need to determine the voltage, RPM, Torque and prop size. The boat should have a cruising speed of 8 kts and a top speed of 12 kts. The hulls will have a 16:1 L/B ratio with the widest section 2/3 aft and wave piercing bow. How do I determine the proper electric motor characteristics. I know that the higher the voltage, the less weight and the smaller wire required to operate the motor. On the other hand the higher the voltage the greater the safety issues. The RPM is variable on an electric drive by utilizing a chopper circuit (PWM) to control it as well as gearing if required. That leaves the torque and prop specs which are inter-related. Can anyone tell me how to get started on finding the answer to these questions?

 

Torque is unlike power changed trought a gearbox.

If you know the popellers torque requiremnt at diferent speed and the gearing you can easely find how big engine you nead.
A frequensy controlled electic engine can keep the same torque at all rpm's.

Not shure if this answers your exsact question.