These are my adaptation for my RC tugboat with imitation Kort nozzles (maybe I'll print some realistic nozzles in the future?). My 1st print was likely under-pitched, so I'm going to make another attempt with a steeper pitch. See print and performance info in the "Misc Notes” section.
As requested, here are some photos of my prints. Using a Printrbot Simple Metal with a heated bed, I printed these with Hatchbox gray PLA (1.75mm) with the bed at 60C and the Extruder at 190C (although values vary from sensor to sensor, so just use them as a guide), running at 50mm/s and a layer height of 0.10mm. I used full support, 50% infill, a raft, full fan except for the 1st layer, and my bed is Kapton tape with high-hold hairspray (it works excellent for me, but pick your poison).
These are 40mm OD, a 10mm diameter hub, and a 3mm shaft. Since the SCAD file extends the hub length equally in both directions, I shortened the non-shafted end (I use 2mm set screws to lock the prop D-slot in the prop shaft) by 3.5mm in Sketchup so it wouldn't contact the leading edge of the rudders.
I did a bollard-pull test in the bathtub with the stock Southampton/Richardson (RC tugboat) props and gearbox, and it registered 2.6amps at full ahead, at 370grams of pull. I didn't measure the (pitiful) astern thrust with the stock props, but the current draw was less than ahead, at 2.1amps. With these 3D-printed props I measured 210grams of thrust in ahead AND astern, with a current draw of 2.1amps. So proportional thrust (great!) but less of it (likely due to a lack of pitch). This was my 1st attempt, and I'm currently rendering a 2nd set with more pitch and experimenting with the blade twist (thanks for the note on counter-twist: I totally forgot to change that the 1st time).