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January 17, 2013

Next generation US submarines will refuel once every 50 years and have quieter electric drive

The heart of the planned ballistic missile Ohio Replacement (OR) program will be built around a drive that will not need to be refueled for the 50-year life of the boats and cuts out potentially noisy direct mechanical connection to the drive train. In other words, the Navy’s next-gen subs could be almost silent, and keep running for a half-century straight. The Navy is developing an innovation that attempts to give OR boomers the quietest nuclear engine yet by going to an electric drive.

The Navy wants to use the power from the reactor to create an elaborate electrical grid inside of the submarine. The reactor power would feed the grid and in turn the electric motors that would drive the boats. Eliminating the mechanical connection would mean less noise under water. The set up would also free up power previously devoted to driving the ship. Currently anywhere from 75 to 80 percent of the power from a nuclear submarine is devoted to driving the ship through the water. Extra power could be routed to other systems like sonars and potentially unmanned underwater vehicles.



Current submarines have a direct mechanical connection to the props that drive the boat. Steam turbines driven by the nuclear power plant go through a series of mechanical gears that translate the high torque power from the nuclear plant into lower torque energy needed to propel the ship. All of those mechanical connections can generate noise, the bane of the submariner.

This will be the second try for the Navy to use electric drive subs. The service experimented with the technology in the 1960s and 1970s but found the boats equipped with the drives to be underpowered and maintenance heavy.

Currently the US navy fields 14 Ohio-class boomers packing 24 Trident II D5 intercontinental ballistic missiles. (The first four Ohios were converted to carry missiles with conventional warheads).

“There are still going to be midlife upgrades but the refueling portion is effectively eliminated which allows us to reduce from today’s 14 Ohios to reduce down to 12 Ohio Replacements,” Stackley said.

The original Ohio-class builder General Dynamics Electric Boat hasn’t built a boomer in more than 20 years and the durability of the drive and the boats to last until 2080 is a tall order.

Added to the pressure is a Pentagon imposed cost cap that reduce the cost of the boat from about $7 to 8 billion down to $4.9 billion. But the Navy will have little margin for error if they want to keep the price tag that low.

The Navy has already delayed work two years as part of its 2013 budget. Currently the first OR boat is scheduled to begin construction in 2021 for a decade-long construction and development process. The super-silent boat is scheduled to make its first patrol in 2031

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