Propeller cavitation criteria (Burrill)

The Burrill cavitation criterion is an empirical chart method for sizing propeller blade area against cavitation, developed by L.C. Burrill in 1943. It plots the thrust loading coefficient tau_c, thrust over dynamic head on the projected blade area, against the cavitation number sigma_0.7R referred to the 0.7R section, with curves of permissible percentage back cavitation drawn from systematic uniform-flow tests. The designer enters sigma_0.7R, reads the allowable tau_c for the chosen back-cavitation limit (commonly 5 to 10 percent for merchant work, less for warships), and back-solves the minimum projected or developed blade area ratio. It is a first-approximation tool: the curves carry no inflow non-uniformity, so a final design still needs cavitation-tunnel checking in the real wake.