It does make sense that you could run 3 blades and not change the RPM by virtue of the controllable pitch. On my boat, 5 bladed props of the same diameter are better for getting up on plane, and run a pit smoother than 4 blades, but you actually lose about 2% on the top end. You get the same forward motion (31 inches) x-slip, per rotation, yet there is some added "interference" casued by the extra blades in cruise. There is less fixed pitch on the 5 blades. Now if you could just get an Archemedic screw to run in the air or water on the end of a shaft, one could get almost a turbine's smoothness
