Morning Derek, thanks for the feedback, hope all's well with you.
Each drive line will indeed use two thrust races, one for forward thrust and one for reverse. They will both pass their thrust forces to the motor mount. Inside what I'm calling the 'thrust assembly' is a collar that can be locked onto the propshaft with one of the thrust bearings between the that collar and the main motor mount. Then as long as there's a little clearance between prop and P Bracket, that bearing should take forward thrust. The second thrust bearing is going motor side as the propshaft passes through the motor mount, between the motor mount and the coupling, that will take reverse thrust and again apply it to the motor mount. Hope that makes sense, I'll get some better pictures to illustrate. The couplings will allow a small longitudinal movement, but it will be minimal once adjusted.
And as to why do it at all... Well, I think it's all resulting from wanting to isolate the motors from the hull to reduce transmitted sound / whine to the hull. Once I decided to use rubber mounts, that means the motors can move if sufficient force is applied to them, and as they're rated at 1,600w, that could get messy... So I felt the only way was to then remove that thrust force from the motors altogether, and this is my solution. I do agree that the motors should be able to take any longitudinal forces they generate via their shaft bearings, but in my head that force transmitted through the motor itself via ball races (not full on thrust bearings) is not ideal. Just my view... So all these motors should have to do is spin, all forces generated by them will be absorbed (or damped) elsewhere, that's the aim. I also wanted to build the driveline in one assembly rather than rely on the hull itself for alignment. It's going to be a large wooden hull after all that may flex.
As always, we'll all have to wait to see if all the effort is worthwhile..!
Very best regards and a Happy New Year to all.
David.