In the January ASCE Journal of Hydraulic Engineering , Rorres reports that the output of Vitruvius's screw is fairly close to that of the optimal 8-bladed screw. In addition, its ratio of inner to outer radius is within 7 percent of the optimal value, and its pitch ratio is within 27 percent. No doubt, many generations of experience went into the design of the screw that Vitruvius described. It has also proved valuable in installations where damage to aquatic life must be minimized. Stein, S. 1999.
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