Magnetic–Mechanical Performance Analysis and Experimental Validation of Noncontact Coaxial Magnetic Gear for a Contra-Rotating Propeller in an Electric Outboard

To reduce carbon dioxide (CO
₂
) emissions, it will be necessary to increase the efficiency of ships, and one approach to consider is the contra-rotating propeller (CRP). A CRP system can significantly improve the propulsion efficiency by recovering a part of the energy loss to the rotational flow and could reduce fuel consumption. Magnetic gears have significant advantages compared with mechanical gears in terms of low vibration, noise, abrasion, reliability and high efficiency driving, and overload protection, due to the physical isolation of the input and output shafts. Using the specifications of an electric outboard, the outer diameter and gear ratio of the magnetic gear were selected and a main effect analysis was performed to determine the sensitive design variables. Then, an optimal model was proposed using the response surface methodology, for effective design variables selected by the main effect analysis. In addition, the vibration stability of the optimal model was verified with a one-way coupled (magnetic-mechanical) performance analysis, based on the results of a 3-D magnetic field analysis.