[freebeard]

My proposal most closely matches the 'gravitation water vortex' in Permalink #71. It is axial flow while the Francis turbine is centrifugal flow. What they do have in common is that the mechanical parts are completely above the flow of water.

I'm thinking about a pipe and shaft that is 4-6ft long, to gain from potential energy as well as the torque from rotating water column. That may not work because of added skin friction.

At 1hp it'd be a glorified water flow meter.