Table 2: The effect of prototype roughness on prototype efficiency (nq = 50) [7] Number of Prototype Conditions Assumed surface roughness Ra of various components (microns) Calculated drop in hP , % Spiral casing Stay vane, guide vane Runner (internal) Disc friction Draft tube 1 0.9 0.4 0.4 0.4 0.9 No drop 2 0.9 0.8 0.8 0.8 0.9 0.07 3 0.9 1.6 1.6 1.6 0.9 0.20 4 0.9 3.2 3.2 3.2 0.9 0.39 5 0.9 6.4 6.4 6.4 0.9 0.66