Hybrid Electric Drive Systems in the United States Navy

With an increasing instability and cost fluctuation in the world energy markets, it has become more important to increase the US Navy fleet’s overall fuel efficiency. The Navy’s Energy Program for Security and Independence sets forth goals to reduce its overall consumption of energy and decrease its reliance on petroleum. One way that helps accomplish these goals is through the use of hybrid electric drive systems to replace gas turbine engines to accomplish lower ship speeds. Although gas turbines are power dense and fairly efficient at full load, their fuel efficiency decreases drastically at the lower power levels used when slower speeds are required to accomplish the ship’s mission. It is in this lower speed range where operating gas turbine generators closer to their optimum efficiency levels and powering an electric motor saves a significant amount of fuel. This paper will discuss two in-service systems developed for various US Navy ships: the Hybrid Electric Drive (HED) system for DDG 103 and the Auxiliary Propulsion System (APS) for LHD 8 and LHA 7. It will describe each of the two configurations and their histories, how they are implemented and increase the capability of the ship, and the resulting fuel efficiencies that have been realized with their use.