Still looking for a practical solution for the bearing at the bottom end of the screw.
Problem is that that bearing is, to all intents and purposes, in the river.
I asked a manufacturer of marine "cutless" bearings but it's not spinning fast enough for one of them.
So looking at ceramic and stainless ball bearings now - anybody got any suggestions?
I was thinking, have a conventional top bearing (maybe even simply use the gearbox bearings) to take radial and thrust loading, it's out of the water and accessible for maintenance.
so the lower bearing only has a static radial load - easy job...
Also top shaft has to be meaty enough to take the turbine torque (about 75mm dia). Bottom shaft only needs to support 1/2 the weight of the screw, less than a ton