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CHIPS Articles: Driving Navy Innovation: Turboelectric to Hybrid Propulsion

Driving Navy Innovation: Turboelectric to Hybrid Propulsion
By Rear Admiral Kevin R. Slates - March 25, 2015
Ninety-eight years ago today [March 23], the Navy deployed a new technology on USS New Mexico (BB 40) that was then hailed as one of the most important achievements of the scientific age: the turboelectric drive. Before this major event, ships used a direct-drive steam turbine, which started with the HMS Dreadnought. Direct drive turbines were very efficient at faster speeds, but at slow speeds they wasted energy when the propeller turned too quickly, causing cavitation. Since the average underway speed of battleships was under 15 knots, this proved to be an issue.

The newly designed turboelectric drive used only one turbine, and rather than driving the propeller shaft, it turned one or two electric generators. The electricity was then routed to electric motors mounted to the propeller shaft heads. Using this method, the turbine would turn at a constant, highly efficient rotation rate, while the electric motors would turn at the most efficient speed to turn the propellers. For full backing power, the electric motors were simply reversed, which eliminated the need for several pieces of equipment and steam piping.

The decision to install the turboelectric drive proved more economical, fuel efficient, and helped improve maneuverability. This innovative technology gave USS New Mexico a strategic advantage over her sister ships, and the nickname, “The Electric Ship.” USS New Mexico would ultimately become the flagship of the newly-organized Pacific Fleet, and an essential part of the war effort during World War II.

The Navy continues to drive toward new technologies that increase combat capability. Over the past six years, with the commissioning of USS Makin Island (LHD 8) in 2009 and USS America (LHA 6) in 2014, the Navy included auxiliary propulsion systems (APSs) on our newest amphibious platforms in addition to the main gas turbine engines. Ships equipped with APS use less fuel at slower speeds, which represents the majority of time amphibious ships operate. During slow speed operations, the APS draws electrical power generated from the ship’s service generators, which are used for HVAC systems, lighting, combat control systems, etc., to assume the full propulsion load.

This greatly increases fuel efficiency by being able to shut down the gas turbines engines, which are efficient at high speeds, but inefficient at slow speeds. This can allow the ship to remain on station longer, extend the time between refueling, or transit greater distances which directly increases the ship’s ability to respond in times of combat or crisis.

The next generation of energy efficient propulsion is the Hybrid Electric Drive Electric Propulsion System (HED EPS), which is planned to be installed on Arleigh Burke (DDG 51) Class Flight IIA ships.

HED EPS attaches an electric motor to the propulsion plant to enable the ship to draw power from the ship’s electric generators and shut down main propulsion engines. Similar to the USS Makin Island and USS America, using the ship’s electrical power for propulsion at slower speeds can save tremendous amounts of fuel. For example, using HED EPS 50% of the time can increase time on station by as much as two-and-a-half days between refueling, which can provide extra time at on station or greater endurance when the ship’s Captain and crew may need it most.

If you have an energy idea you believe will help the Navy improve our ability to perform our mission and propel us into the future, we’d like to hear about it. You can email our energy team at energywarrior@navy.mil and download the Navy’s Energy Warrior App here.

To learn more about the Navy’s ongoing energy initiatives, visit http://greenfleet.dodlive.mil/energy.

Reprinted from the Navy History Blog.

Rear Admiral Kevin R. Slates
Rear Admiral Kevin R. Slates

Photographed from an airplane, while steaming in line with other battleships, 13 April 1919. Note S.E.5A airplane atop the flying-off platform atop the battleship’s second turret. Naval History and Heritage Command Photograph.
Photographed from an airplane, while steaming in line with other battleships, 13 April 1919. Note S.E.5A airplane atop the flying-off platform atop the battleship’s second turret. Naval History and Heritage Command Photograph.

PHILIPPINE SEA (Oct. 22, 2014) The amphibious assault ship USS Peleliu (LHA 5) is underway as part of the Peleliu Amphibious Ready Group and is conducting joint forces exercises in the U.S. 7th Fleet area of responsibility. U.S. Navy Photo by Mass Communication Specialist 1st Class Joshua Hammond.
PHILIPPINE SEA (Oct. 22, 2014) The amphibious assault ship USS Peleliu (LHA 5) is underway as part of the Peleliu Amphibious Ready Group and is conducting joint forces exercises in the U.S. 7th Fleet area of responsibility. U.S. Navy Photo by Mass Communication Specialist 1st Class Joshua Hammond.

PCU Zumwalt (DDG 1000). U.S. Navy photo.
PCU Zumwalt (DDG 1000). U.S. Navy photo.
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