Auxiliary Electric Drive (AED) Application in U. S. Coast Guard Cutters

摘要

Shielding the United States from threats delivered by sea, saving those in peril on the sea, and protecting the sea itself, the U.S. Coast Guard (USCG) is a military service with uniquely diverse and dynamic missions that range from national security and safeguard of the marine transportation system, to law enforcement protection of our natural and living marine resources. USCG ability to operate in these dynamic, geographically vast, and diverse physical environments requires purposeful asset allocation to ensure specific capabilities and capacities are ready, adept, and agile to shift among its missions as needed. Supporting this asset apportionment, the USCG balances limited resources between competing priorities. These priorities include creating future operational capacity and capability through new surface cutter recapitalization, legacy cutter modernization and service life extension overhaul, as well as persistent pursuit of high return strategic investments which gain significant operational capability and capacity at far lower Total Ownership Cost (TOC), with little performance trade-off or compromise. Moreover, the magnitude of USCG's unique mission diversity adds further challenges to the complexity of its resource balance. This mission diversity requires major surface asset cutters to operate across a wide range of propulsion drive loads, including high-speed transit / intercept, as well as long cruising speed endurance. As a result, the major USCG cutters with mission requirements for these widely varying loads have, by design necessity, propulsion plants characterized by very high-power density (VHPD), such as combined diesel and/or gas turbine (CODAG/ CODOG) systems, or very high-power to weight ratio high-speed main propulsion diesel engines (MPDEs). While these VHPD mechanical propulsion systems offer considerable advantages for military vessels, the design trade limitations implicit in maximizing opposing performance characteristics inevitably confine mechanical propulsion systems to applications optimized for high performance ranges. Nonetheless, many USCG mission environments require disproportionally lower propulsion power loads, these demands on machinery are exacerbated by increases in environmental regulatory control, slower transit speeds, and lengthier low-load loitering operations. Accordingly, this paper examines a strategic investment opportunity to expand overall cutter mission performance through an auxiliary electric drive (AED). Applying existing excess electrical power capacity to produce auxiliary propulsion during low-speed operations, without the complicating requirements for electrical power regeneration or tactical main propulsion (sic. hybrid-electric drive systems); a cutter AED will reduce MPDE maintenance, significantly reduce engine hours, increase mean time between overhaul (MBTO), lower harmful exhaust emissions, and improve fuel efficiency. The proposed AED includes electric motor(s), mechanical drive, switching and control systems, and other related equipment. Further, this paper examines theoretical performance limitations, implementation options, ship speed estimates, and TOC reduction opportunities for a cutter AED.