A high-speed gas turbine engine on board the U.S. Navy's first Littoral Combat Ship (LCS) broke earlier this month and will need to be replaced, but officials don't expect the mishap to affect the ship's testing schedule.
The incident took place Sept. 12 while the USS Freedom was operating off southern California. The ship shut down its two Rolls-Royce MT30 gas turbines after "high vibration indications" were seen in the starboard engine, according to Cmdr. Jason Salata, a spokesman for the Naval Surface Forces command in San Diego. The ship returned to port using its diesel engines.
Subsequent examination of the broken engine showed that turbine blading had broken off and damaged the unit, Salata said.
The incident comes at an awkward time for Lockheed Martin, prime contractor for the Freedom, which is locked in a competition with Austal USA, the builder of LCS 2.
Later this year, the Navy is expected to choose one of the designs as the basis for 51 more LCS vessels and award a construction contract for a batch of 10 ships.
Freedom was the first of the LCS ships to be completed when it was commissioned in November 2008. The ship is powered by a combination of gas turbines and diesels that can drive it to speeds well over 40 knots.
Freedom's power plant features Rolls-Royce gas turbines, the first to be fitted in a U.S. Navy ship. Nearly all Navy gas turbine ships since the 1970s have been powered by variants of the General Electric LM2500, which is also in wide use worldwide. LM2500s often run 15,000 to 20,000 hours before they're replaced.
Both the Rolls-Royce and GE engines are marine versions of well-tried aircraft engines, and the MT30 is part of the Rolls-Royce Trent engine family. Although the MT30 is a new marine engine, Trent aviation engines have achieved more than 30 million flying hours, according to the company. The engine will also be used on the DDG 1000 Zumwalt-class destroyers, and on Britain's Queen Elizabeth-class aircraft carriers.
Lockheed chose the MT30 because it is more powerful than the LM2500, although it is also larger and heavier. The engines on the Freedom each have a nominal rating of 36,000 kilowatts, or 48,280 horsepower. Most versions of the LM2500 are rated at about 26,000 horsepower. The engine turns at about 3,300 revolutions per minute.
REPLACING AN ENGINE
Removal of the damaged engine will allow the Navy and its contractors to try the ship's engine changeout procedure. All ships have features that allow the engines to be removed and replaced, and Freedom's design provides for engines to come up through the ship's intake stacks, according to Lockheed.
"The changeout process requires a few days for set-up and removal, and the replacement can be done within 48 hours," said Kimberly Martinez, a spokesperson for Lockheed.
The Navy will allow up to a week for the changeout, Salata noted.
The Freedom, which earlier this year carried out a demonstration deployment to the Caribbean and Central America and took part in its first naval exercises, is designed to conduct engine changeouts while deployed. Eventually, the ships will carry equipment to change the engines, although the Freedom wasn't yet carrying that gear when the engine was disabled. The Navy, rather than performing the changeout operation at the naval base in San Diego or a shipyard, will handle the evolution at Port Hueneme, Calif., a small base that supports warfare, construction and maintenance units.
"Port Hueneme as a port facility has characteristics of the likely locations in which a deployed LCS would conduct an engine changeout," Salata said.
Experts from the Naval Sea Systems Command, Lockheed Martin, Rolls-Royce and the Navy's Ship Systems Engineering Station in Philadelphia will assist in the changeout, Salata added. Philadelphia is home to NAVSEA's land-based test site, which runs various configurations of a number of naval propulsion units, including the MT30.
The LCS already was scheduled to go to Port Hueneme in late September to carry out handling exercises and tests of its mission modules. While the engine is replaced, Freedom's crew will practice removing a mission module - a set of equipment tailored for a specific mission such as mine warfare - and loading another. Because the mine warfare module is not yet ready, "models designed to replicate the space and weight" of the modules will be used "to demonstrate the onload installation and fit of those modules," Salata said.
The damaged engine will be taken by Rolls-Royce for study to determine what caused the problem.
source: Defense News
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