This paper outlines the hydraulic design for the R.H. Saunders replacement runner. The six-bladed propeller runner was numerically optimized based on 3-dimensional flow simulation. After finishing the numerical design, the new runner was tested in pre-development tests in the Sulzer Escher Wyss hydraulic laboratory in Zurich. These measurements and later on those with the completely homologous model have confirmed that the numerically optimization has been successful. Results of the numerical flow visualization as well as experimental results obtained from the model tests are presented.