Contrarotating Electric Drive for Attack Submarines

Abstract

This paper addresses certain issues relating to the viability of contrarotating (CR) electric drive for attack submarines. Topics include CR propulsion's potential benefits, electric drive advantages, and combining contrarotation with electric drive engine room concepts. CR propellers provide propulsive coefficient (PC) increases compared to open-type and performanceenhanced single p r e pellers. The maximum submarine propulsion plant power capacity could therefore be reduced with this PC increase, potentially resulting in a smaller, lighter propulsion plant. This paper concludes, however, that contrarotation shows no propulsion plant weight savings against electric drive attack submarines with performance enhanced single propeller designs. Weight improvements in the power generation plant and certain steam plant and electric plant systems are offset by weight increases from the additional shafting and bearing requirements for the CR shaft. Contrarotation is currently more advantageous for nonnuclear ships, where significant fuel savings are achievable with its higher PC.

Submarine Hydrodynamics

“…Thus, in principle, the propulsive efficiency can be much greater than for a single propeller. Contra-rotating propulsion was used successfully on the USS Jack from 1967 to 1989, demonstrating a 10 % increase in propulsive efficiency (Dutton 1994).…”