Development of a Marine Propeller With Nonplanar Lifting Surfaces

The principle of nonplanar lifting surfaces is applied to the design of modern aircraft wings to obtain better lift to drag ratios. Whereas a pronounced fin or winglet at the wingtip has been developed for aircraft, the application of the nonplanar principle to marine propellers, dealt with in this paper, has led to the KAPPEL propeller with blades curved toward the suction side integrating the fin or winglet into the propeller blade. The combined theoretical, experimental, and practical approach to develop and design marine propellers with nonplanar lifting surfaces has resulted in propellers with higher efficiency and lower levels of noise and vibration excitation compared to conventional state-of-the-art propellers designed for the same task. Conventional and KAPPEL propellers have been compared for a medium-sized containership and a product tanker. In total, nine KAPPEL propellers and two conventional propellers have been designed, and models of all propellers have been examined with respect to cavitation and efficiency in the open-water and behind conditions. Casting procedures, measurement procedures, and stress analysis methods for the unconventional geometry of the KAPPEL propeller have been developed. Furthermore, the KAPPEL propeller has been applied in full scale to the product carrier investigated. Sea trials with the conventional propeller and the KAPPEL propeller have been performed and have proved an efficiency gain of 4% in favor of the new propeller. The improved efficiency was obtained at lower propeller-induced pressure fluctuations. The correlation between the theoretical, experimental, and full-scale results is discussed.