A simple and reliable alignment method is to fit telescoping tubing, be it brass, aluminum ect, to both the prop shaft and the motor shaft until the tubing fits snuggly on to each. Essentially it directly aligns the shaft to the motor. Once done, adjust, presumably, your motor mount to align with your shaft and fix into place. Once the glue has dried, remove the tubing by withdrawing your shaft and reinstall same, but fit your universal. Alignment should be very close with little to no angular offset to be taken up by the universal.
Hope this helps.

Thanks Steve for your thoughts. Appreciate the identification of the coupling type.
Agree with your recommendations on alignment. Guess to paraphrase a military expression "Time spent on alignment is seldom wasted!"
That coupling seems to accommodate any slight mis match by straining as you suggest. The Hookes joint type absorbs it by speeding up and slowing down every half rpm. Accounting for the noise and vibration.
My first experiences of the "stepper motor" type coupling are encouraging. So much so ordered a spare set yesterday. They are inexpensive anyway.
Biggest concern is if any straining will ultimately result in fatigue, which might cause failure.
Time will tell.
Cheers
Rowen (right way up!)

Hi RHBaker,
The coupling on the right of your photo is a zero backlash coupling mainly used for servo or stepper motors connecting to a ball screw on machinery, there is nothing wrong with using this type of coupling except it does require a high degree of alignment in both planes (best done with a dial indicator) between the driver and driven shafts.

It may be quieter even with some misalignment possibly due to the coupling "straining" this may transfer forces onto the motor bearings or shaft bearings therefore making it quieter.
A simple test would be to use an Amp meter, running the motor with the new coupling then perhaps free then with the old coupling comparing the findings, this should give you an idea if unwanted force is being used to spin the prop shaft.
Alignment is always critical what ever coupling is being used.
Cheers,
Stephen.

Thanks Rowen will look for them.
Rick

Rick,
Have bought a couple of sets, one from Banggood and one from Amazon.
Suggest search for "couplings" on either site and you will find a whole range.
Think buying from Amazon is more predictable, but they all seem to be made in the Orient.
Rowen

Where do you buy the coupling .Rick

Have now tried this coupling style in two models.
Thoughts are:
1) Slightly more bulky than the hookes joint style they replaced.
2) Not as flexible, so installation requires slightly more room.
3) Quieter and less vibration.
4) By examininging the "spiral" cuts the coupling alignment can be assessed. If it is misaligned the spirals either tighten up or get wider.
5) Much to early to assess life.
On balance am satisfied and will retrofit other vessesl as their annual overhauls dictate.