Integration of permanent magnet motor technology

Studies begun in the 1990s by General Dynamics Electric Boat (EB) and its partners determined that permanent magnet (PM) radial field propulsion motors offer a relatively mature, low risk technology with significant near-term advantages for improving torque density, efficiency, and reliability. Although electric powered ships have been built throughout the 20th century, the majority of ships used mechanical drives for propulsion, due to adverse torque density, reliability, and maintenance aspects of electric propulsion alternatives. The EB stepped approach has built and tested 17 hub and three rim-driven PM motors up to 4.47 MW and 107 kN-m of torque to validate the technology and design toolsets for preliminary designs of large 21st Century PM propulsion motors. Conceptual designs of commercial external rim-driven PM motors integrated with advanced propulsors also offer millions of dollars in potential fuel savings compared to conventional hub-driven propulsion pods.