@pacificmeister this is my seal design on my second version design. It works very well. The vibration has been eliminated and smooth. Please notice that I do CNC machining parts. Not 3D printing. Just for reference.
I use larger shaft and through a pair of four-point angular contact bearing to support the shaft thrust load and stable the propeller shaft. And I am only using one seal to minimize the friction load.
Good luck to you all
Marco H
Very nice! Good idea with the angular contact bearings, I don’t really trust these litttle needle roller thrust bearings I have been using. Looks like you can easily check and replace the single shaft seal by taking of that end cap. How is that sealed?
@pacificmeister yes. Your are right, the endcap can be easily remove and simply check and replace the seal in few minutes. Easy maintenance design. Following attached detail of the seal been disassembled. For your refer.
@Marco_Hou Very nice design. Being able to CNC would be the best.
What are the 2x black ring beside the bearings?
These are two locking nuts to locate bearings onto a shaft. 
Oh I see now thanks haha. Also looks like you have a universal joint for the coupler?
Have you had success with this setup?
This parts look like they can all be done on a lathe except the key ways? I might do a similar design for my rev 2.
Yes, my rev 2 works very good, had lot of fun to foil on the water.
This universal joint is highly recommended to your rev 2. It transfers higher torque better than ordinary shaft coupling to the propeller. After I put it on by replace a solid connector. It eliminates the error of concentric between two shafts. Just works well, smoother and quieter. But high quality universal joint like I bought is much expensive 
. I think it is worse to solve the problem.
