Hi Stavros,
good to get your two bob's worth.
Our models are usually made from wood, in its various forms, or fibreglass, and as such flex, and move with temperature, and moisture content. I agree that IF our motors and shafts where perfectly aligned, then all will be quiet and smooth.
In real life, this is just not going to happen, with varying degrees of misalignment.
Also, the practice of fixing the motor solidly to the hull, as is the shaft tube/bearings, simply ensures the best sound path from the motor to the sounding box, the hull, so that any vibration/noise is amplified, usually more than somewhat.
Even though I've been guilty of solid fixing, I am now going back to rubber mounting my motors in all my boats.
They do run quieter, but necesitate a coupling to allow for this.
I'm sure Mick is on the right track, and will achieve what he's looking for. Just wish I had access to machine tools, and had the skills to use them
cheers
vnkiwi