Seapower - May 2009

Propulsion Solutions
Electric ship initiatives offer flexibility, increased warfighting power

By RICHARD R. BURGESS, Managing Editor

Directed Energy

In many warships, a mechanical drive system is used for propulsion. The engines are mechanically connected to reduction gears, which are connected to the propeller shafts. The engines also mechanically power generators or motors that drive generators to provide electrical power throughout the ship. Auxiliary generators are commonly used to produce power.

With conventional mechanical drive, a ship is restricted in design to a layout in which the engines and reduction gears are typically located in the lower aft hull. One advantage of electric drive is that the engines and generators can be located almost anywhere in the ship, connected to the drive motor by the transmission wiring. The flexibility allows a designer more freedom in designing survivability into a ship. The fact that the propeller shaft is rotated by a quiet electric motor rather than a mechanical reduction gear also reduces the acoustic signature of a ship.

A hybrid electric drive is a combination of the two concepts in the same propulsion system, whereby the operator has the option of using electric or mechanical drive, depending on the speed and fuel efficiency desired. The concept is used in modern automobiles, such as the Toyota Prius.

San Diego-based General Atomics and DRS Technologies, Parsippany, N.J., are teamed “to explore technologies to improve fuel efficiency,” Petersen said. “The goal of the hybrid electric drive project is to reduce fuel consumption, leading to reduced dependency on fossil fuel.

“Further, the hybrid electric drive system could increase mission effectiveness through longer time on station,” he said. “Their project entails developing hardware to be tested at the Philadelphia DDG 51 Land-Based Engineering Site.

The Navy’s electrical ship programs are benefiting from innovative industry participation.

■ The concept promises greater ship fuel efficiency and flexible energy for future weapons.

■ Superconducting and permanent magnet motors compete for adoption.

■ Power transmission and switching technology present challenges.

With the help of industry, the Navy is maturing the solutions proposed for the challenges of electric ship technology, a transition that promises flexible design options, greater fuel efficiency and sufficient power for the mission systems of the future.

With innovative concepts such as hybrid drive, more powerful electric motors and generators, and greater electrical storage capacity and distribution, the Navy is designing and building ships to capitalize on the technology.

“Across the Navy, from basic science to in-service applications, initiatives are being established based on technology gaps and needs,” said Capt. Lynn Petersen, deputy program manager of Electric Ships for the Navy’s Program Executive Officer for Ships. “New ship designs are taking into account the benefits of all electric and hybrid drive technologies.”

Electric drive is a propulsion arrangement in which a ship’s engines — typically gas turbines, steam turbines or diesel engines — power an electrical generator. The generator, in turn, powers a large electric motor, which is connected to the propeller shaft. Generators also provide power to the ship’s combat systems, lighting, heating, air conditioning, elevators and other missions and “hotel” requirements.