Sizing Segmental Section--Commercially Available Propellers for Small Craft

Abstract

Open water characteristics for segmental section propellers are synthesized as a function of pitch ratio, expanded area ratio and number of blades using modifications of the Wageningen B-Screw series polynomials. Thrust and torque limits in a cavitating environment are estimated from maximum thrust and torque load coefficients developed from the Gawn-Burrill cavitation data. Synthesized thrust and torque coefficients as functions of propeller advance coefficient and cavitation number are compared with experimental series data and with commercial propellers of the flat face, segmental section type tested in open water and under cavitating conditions. A procedure for selection of propeller diameter and pitch ratio for best performance -- maximum efficiency and minimal cavitation -- is presented, with number of blades and expanded area ratio being preselected. The method is directed to selection of commercially available propellers for small craft, in lieu of more costly custom design propellers. Reference. is made to computer routines· for expediting propeller selection using synthesized performance data.