This file package includes options for two different stern modifications to a 1/72 US Virginia submarine. While the files were specifically designed for use with Virginia, they could be applicable to other boats with simple scaling or with some physical modification of the printed parts. 
 
The stern section terminates at a 67mm diameter hull profile, extends for approximately 127mm, and ends in a propeller interface of 11mm. 
 
V1: 
Consists of two parts
Designed to have a brushless motor bolt directly to the shroud
Hole spacing for the motor is 25mm
The shroud swivels, leaving the stern section stationary
Motor spec'd for the prototype was a 650kV unit with an overall length from motor face to rear of approximately 30mm. 
 
V2: 
Consists of five parts
Designed to allow you to take advantage of a cylinder with an existing motor
Shaft runs through the first stern section, then enters a universal joint, then terminates at a secondary shaft that is attached to the propeller
It is imperative that you put the universal joint's swivel point directly between the two swivel holes or binding will occur.
 
NOTE: I do not supply motors, shafts or universal joints. These files are designed for use by people with the basic skillset required to assemble, test, trim, modify and otherwise work the parts into their project. Good luck!