I have now installed the motor mountings and propeller shafts. I find its a job that has to be done "all together", to ensure as far as possible, that all is correctly in-line and will run as true as possible.
So first thing is to put some masking tape on the underside of the hull, mark the centre line, then from the centreline, equally space the propeller shaft "runs" to these lines. I had already got these in place, when I installed the rudders, so I only now had to drill the initial hole to make a start for the propeller tubes.
Don't forget that these holes are not "circular", but a very long "oval" shape, and it takes some careful drilling initially, followed by a round file, to get the shape almost right.
now you can slide the propshaft tubes through inside the hull attach the universal joints and then on to the motor drive shafts, making sure the mounting screws for the motors are only "finger tight", so you can remove them easily later. I then placed some balsa blocks between the prop tubes and the hull underside to then line up the motors with the hull internal floor, to make sure the mounts sat flat against it.
once happy, I marked the hull floor to show position of the motor mounts, removed the mounts and shafts, removed the motors from the mounts and them proceeded to bond the mounts to the hull floor with glass fibre paste, this i pushed in to the big holes i predrilled in the mounts to ensure the glass fibre mixed with the layer applied to the hull floor, to help make a full bond.
once this was dry I refitted the motors and reattached the drive couplings and propeller shafts. then with the balsa blocks in place, I initially used some epoxy resin mix to affix the propeller shafts in line to the underside of the hull . Once this was dry, and rechecking the angles of the propeller shafts, i then added a further layer of glass fibre paste to the hull holes made for the shafts to exit, to fill up the gaps around the shaft exits. Last job was to add a propeller shaft support, 20mm from the end of the shafts, behind the propeller, to add a bit of support to the tubes, to reduce the risk of excess vibration when under load.