Experimental investigation of single blade loads by captive model tests in pure oblique flow

Maneuvering motion is a critical off-design condition experienced by the propeller during realistic operations. Failures of the propulsive system, loss of efficiency and modification of the propeller side effects (propeller-hull induced pressure and noise) are the undesired consequences of these working conditions. Free running model tests, still representing the primary approach for a reliable performance assessment, requires facilities and devices that are not commonly affordable; alternatively, rectilinear towing tank can be used for maneuvering investigations by static or dynamic tests and can be a valid alternative to investigate propeller performance in off-design. On these basis, in this paper the propeller performance in maneuvering conditions is investigated by means of oblique towing tests in case of a twin screw model equipped with a novel set-up for single blade loads measurements.In the experiments, the drift angle and the advance speed of the model varied systematically, to focus on the relation between propeller operating conditions and loads. Moreover, the averaged and periodic blade loads are compared, in terms of the equivalent drift angle, to the measurements obtained by free running model tests, in order to demonstrate the reliability of pure oblique flow tests for the preliminary quantification of the off-design loads developed by the propeller.