From Cruise Ships to Warships, Electric Propulsion Goes to Sea

Conference covers electric ship technologies

4 February 2011

Electrically driven surface ships have been around since at least World War I, but lately their number has been growing, swelled by demand from cruise lines and navies and by new technologies. Since 2005, the biennial IEEE Electric Ship Technologies Symposium (ESTS) has been bringing together experts from navies, shipyards, industry, and research universities from around the world to discuss the technical challenges to making future electric ships more capable, robust, and less costly. This year’s symposium, scheduled for 10 to 14 April in Alexandria, Va., is sponsored by the IEEE Industry Application, Oceanic Engineering, Power & Energy, Power Electronics, and Vehicular Technology societies, as well as the IEEE Sensors and Systems councils. The American Society of Naval Engineers and the Institute of Marine Engineering, Science, and Technology are technical co-sponsors.

“We will talk about applications in the cruise ship industry, naval propulsion systems, integrated power systems, controls, energy storage, pulsed power, and power quality,” says Steinar Dale, an IEEE Life Fellow and general chair of the symposium.

About 100 papers will be given, with the conference expanded this year from two to 2½ days.

No matter what their mode of propulsion, today’s ships are becoming more and more electrified. For example, ferries and cruise ships provide more high-tech amenities for passengers’ laptops and other electronic gear. Freighters and tankers are converting pumps and other devices from hydraulic to electrical operation. The electrical loads on warships are also increasing, with more powerful radars, lasers, rail guns (which use linear electric motors for firing projectiles) aircraft launchers, and other multi-megawatt loads. Furthermore, many systems, such as the pumps that load and unload tankers, are most active when little or no power is being used to propel the ship.

With electric propulsion, a single generating system can handle all the ship’s power needs. Electrical propulsion also lends itself to more automation, reducing staffing requirements and enabling systems to be linked together. For instance, drive and steering systems could be linked to a GPS to automatically hold a drilling ship’s position constant. And should problems develop, remote telediagnostics can link the drive systems to land-based tech troubleshooting and support.

The electric ships’ diesel or gas turbine engines drive generators that feed power to direct-drive motors. With no long propeller shafts to drive, the systems can be placed almost anywhere, allowing designers to arrange the ship’s spaces more efficiently. The engines are also easier to reach for maintenance and can be mechanically isolated from the hull for quieter and smoother operation.

“Drive motors and propellers can be put in rotatable pods beneath the hull so you don’t need rudders,” explains Dale, who heads Florida State University’s Center for Advanced Power Systems, in Tallahassee. “Most cruise ships are built that way today.” That enhances maneuverability, often enabling ships to dock without the aid of tug boats.

A single generating system used for propulsion and other tasks will normally include multiple engines and generators, not just for reliability through redundancy but for increased efficiency as well.

“Gas turbines and diesels are most efficient when run at full load, so using several, of different sizes, lets you choose which to use for maximum fuel efficiency at any load,” Dale says. “This cuts operating costs.” Using less fuel also decreases carbon dioxide and other emissions.

Distributing the generation system that way also keeps each engine and generator small enough for maintenance at sea, without taking the vessel out of service. And electrical drive systems are more reliable mechanical drive shafts, further reducing maintenance costs.

Distributing power from multiple generators to multiple loads requires a robust, dynamic integrated power grid, Dale says. The grid should be reconfigurable to work around faults or damage that may occur in the system and to provide power to different loads depending on the ship’s mission. That is what makes the system more robust, while improving the ship’s survivability by providing electrical power to vital components.

“That’s especially true of warships, which must safeguard operation not only of the propulsion motors but of the radars, command and control system, emergency systems, pumps and firefighting systems, and weapons systems,” he says.

The intelligent microgrid called for aboard a ship probably could share a lot of technologies with the terrestrial smart grid, he says, but would have to be much more capable, able to deliver megawatt pulses in milliseconds for radars, rail guns, and other devices.

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