L-3 Communications Maritime Systems has started production of hybrid electric drive (HED) propulsion systems, consisting of an electric motor, motor drive, control software, and ancillary equipment, which the Navy plans to install on 36 Arleigh Burke–class Flight IIA destroyers.
The first installations, aboard the USS Stockdale (DDG-106) and Gravely (DDG-107), are set tentatively to start this summer in the ships’ home ports of San Diego and Norfolk, respectively.
The Flight IIA Burkes include the Oscar Austin (DDG-79) and all those forward through to the start of Flight III of the class.
The HED design, Navy and industry officials note, promises sizable cost and performance benefits. They point out that the conventional power architecture for the Burkes, which use four General Electric LM2500 gas turbine engines for propulsion, is designed for maximum power and efficiency at high speeds. The gas turbines, though, are inefficient at lower speeds, below 12 knots or so. Because the ships typically spend as much as half their underway time at lower speeds, the ability to improve low-speed efficiency offers the potential for considerable fuel savings.
The Naval Sea Systems Command awarded contracts in 2009 to DRS Technologies and General Atomics to develop proof-of-concept HED systems. In 2010 DRS won an award for construction of a demonstration system that incorporated an advanced 1.5-megawatt permanent magnet motor.
In 2012 L-3 won an industry competition to build two prototype HED systems, one for environmental and shock-and-vibration testing and the other for integration with ship-control systems at the Naval Ship Systems Engineering Station in Philadelphia. The award included options for follow-on production.
NAVSEA exercised the first contract option last summer for production of the shipsets for the Stockdale and Gravely. In current planning, in following years the company will install four systems per year, with the work coordinated with ship availabilities and the ongoing modernization program for the Burke class, a top-to-bottom refresh of combat, sensor, and machinery systems.
HED introduces electric induction motors attached to the propeller-shaft reduction gears and powered by the generators that provide power for the non-propulsion ship systems. A motor drive converts power from the generators to the frequency and voltages needed for the motors. At low speeds, the electric motors will power the shafts, allowing the LM2500 gas turbines to be shut down, thereby achieving the fuel savings sought.
L-3 points out that for the Burkes’ system, however, only the port shaft will be fitted with a motor, leaving the starboard shaft in the conventional operating mode.
The Navy already has fielded an HED architecture, built by General Electric, aboard the amphibious-assault ship Makin Island (LHD-8), the last ship of the Wasp class of big-deck amphibs and the only one powered by gas turbines (the first seven use diesels). Navy officials report that in its first two months at sea following its 2009 commissioning, the Makin Island showed fuel savings of some $2 million. Another amphib, the America (LHA-6), now in service, has an HED system, and a similar system is going aboard the Tripoli (LHA-7), now under construction.
The L-3 team includes Kato Engineering of Mankato, Minnesota, which provides the induction motor, and Ingeteam, a Spanish firm that builds the motor drive. L-3’s Westwood division provides the switchboards, and the company’s New Orleans site developed the HED software.
Carl Fisher, vice president for business development at L-3 Maritime Systems, said that HED is an “important transition” for thinking about a full-up integrated electric drive system, a longtime Navy goal. The Navy’s newest major surface combatants, the three-ship Zumwalt class, initially were expected to go to sea with an integrated electric drive system using permanent magnet motors. Because of questions about the motors, the Navy decided instead to use an advanced induction motor built by Coverteam.
The Navy plans to fit out the Flight III Burkes extensively with extremely high-energy sensors and weapons, including an air-missile defense radar for detection of airborne and ballistic missiles, and lasers and high-velocity railguns, now in development, which will require intensive bursts of power.
Fisher says the company has discussed the prospect of operating the hybrid architecture in a so-called “power take-out” mode for the Burke Flight IIA program, whereby the electric motor would function as a generator when the ship is running at higher speeds, and then would be able to provide power back to the ship’s service electrical bus. L-3 also is exploring a potential role in developing the power architecture for the Flight IIIs, he said.
Mr. Walsh is a veteran reporter of Navy and Marine Corps news and former editor of Naval Systems Update.