Water Jet / Impeller

I designed and printed this but never had a motor with enough power to give it a proper try
and I didn't want to spend more money on the project so this is as far as I got.

Printed in PETG (the orange parts) and PLA (the white parts), the impeller is 55mm in diameter so you could just use an RC boat prop the same size.

To mount the impeller I got an 8mm nut, drilled out the thread so it slid over the 8mm rod then I drilled a 2.5mm hole in the side of the nut, tapped it to M3. I then ground a flat spot on the 8mm shaft for the M3 screw to lock against. I then set that all in place with thread locker and cut the top of the M3 screw off, the impeller then slid over the nut which was now held fast on the shaft. Did the same thing with a 2nd nut (as you can see in the picture) to stop the impeller coming off the 1st nut.

I'd say a "focusing" exit nozzle would be required to create a good amount of thrust much like the back of a jet engine. That should be nice and easy to design to your specs.

I used the parts below:
https://www.banggood.com/OD-10mm-x-8mm-ID-Stainless-Pipe-304-Stainless-Steel-Capillary-Tube-Length-500mm-p-1057416.html
https://www.banggood.com/8mm-100200285320350mm-Carbon-Steel-Linear-Rail-Shaft-Rod-p-1119330.html
https://www.banggood.com/5mm-8mm-Shaft-Coupling-Rigid-Coupler-Motor-Connector-With-Spanner-p-1070710.html
https://www.banggood.com/8pcs-608-2RS-Bearings-8x21x7mm-Ceramic-Bearings-For-Skateboard-Deep-Groove-Ball-Bearings-p-1144805.html