I must calculate a torque for a immersed shaft ( dia.= 4"; L= 25'-4") equipped with 8 paddles. This assy. Will function like a mixer. Fluid: water (water viscosity for calculation).
I must use the existing equipments for this assy.
The assy. Paddles are welded assy. From a pipe (mounted around the shaft and fixed with 2 screws on the shaft). Around the pipe are welded paddles ( 4 paddles/90 degrees). This shaft will be mount in a reactor (horizontal tank). Tree plillow block bearings supported the shaft inside from tank. Out of the tank is mounted an electric motor P=50HP, r=1800rpm and a gearbox 30:1. The shaft revolution must be aprox. 60 rpm.
Please guide me.

Thanks!
Daniela