I think what you might be able to do is load another ship or submarine in S3D, that has the propeller you want, select the propeller and export the 3d image to and object file which will also allow you to export the mtl file needed for the object. Then, open the submarine file that you want to modify and select the propeller and under 3d Image import the object file that you exported from your source sub/ship. That worked for me when I put 40mm barrels on a twin 20mm AA gun.
I hope that helps