Investigation of single propeller blade loads during turning motion by free running maneuvering model tests

Maneuvering conditions are critical for the ship propulsionsystem, because the performance of the propeller and theside effects related to its functioning (propeller-hull in-duced pressure and vibrations, noise) are completely dif-ferent with respect to the design condition in straight aheadmotion. Thrust, torque and generation of in-plane loads(force and moments), developed by the blade during theperiod of revolution, evolve differently for the two pro-pellers due to different propeller-wake interactions. Theunderstanding and the accurate quantification of propellerloads in these realistic operative scenario is of paramountimportance to design low emission and comfortable ships,fulfilling the requirements of safety and continuity of op-erations at sea. The complete assessment of the problemis very challenging due to the complex evolution of theflow past a maneuvering ship and the consequent interac-tion with the rotating blades. These interactions give riseto complex blade wake/vortex interaction phenomena. Inorder to study in greater details these phenomena, a novelexperimental set-up dedicated to the measure of the singleblade loads was developed at CNR-INM and installed onboard of a twin screw model; in particular, the starboardpropeller was redesigned to house a 6-component trans-ducer attached to the root of one of the blades. In this paperthe single blade and propeller loads will be presented anddiscussed for the case of a twin screw ship in straight aheadmotion and steady turning motion. The most important as-pects of the off-design operation of a marine propeller willbe inspected in detail by the analysis of the cyclic bladeloads, namely the asymmetric evolution of the loads forthe internal and external propeller, the overloading of thrustand torque and the generation of the in-plane loads.