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Ohio Replacement Subs to Shift to Electric Drive

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Ohio Replacement Subs to Shift to Electric Drive

Postby Tom Dougherty » Mon Sep 30, 2013 1:07 pm

Ohio Replacement Subs to Shift to Electric Drive

by Kris Osborn on September 27, 2013 DefenseTech

The U.S. Navy’s successors to Ohio-class submarines will feature an electric propulsion system, making them quieter and stealthier than today’s versions.

The technology for the ballistic-missile subs is being developed by the Navy and General Dynamics Corp. as part of the Ohio Replacement Program, Rear Adm. Richard Breckenridge told Military​.com in an interview. Construction of the boats is set to begin in 2021, he said.

Unlike existing versions, which use mechanical propulsion technology, the replacement subs are designed to have an electric-drive system, Navy officials said. The technology still relies on a nuclear reactor to generate heat and create steam to power turbines, they said. However, the electricity produced is transferred to an electric motor rather than so-called reduction gears to spin the boat’s propellers, they said. “We just take the electricity from those high-speed turbines and use that electricity to drive an electric motor that propels the ship,” Breckenridge said. “It is quieter than a mechanical drive system.”

Evolving global threats require ever more quiet submarines, Navy officials said. The Navy decided to invest in the technology after reaching the limits of trying to silence mechanical propulsion, they said.
“Great minds have figured out how to get those gears whisper quiet,” one Navy expert said. “We did not have any more tools in the bag to get the stealth that we knew we needed for this national strategic imperative.”

The Navy has experimented with electric drive in the past, but it took 15 years for the service to perfect the technology, officials said. The system offers a number of potential advantages, including noise reduction, according to Bryan McGrath, managing director at FerryBridge Group LLC, a defense consulting firm based in Easton, Md. “When you have the motor tied directly to the propulsion shaft, that should eliminate some of the noise,” he said. Electric propulsion can also help ships generate more on-board power for electronics, sensors and weapons systems, McGrath said.

“Electric drive makes a lot of sense for submarines,” he said. “There is some technical risk in moving from mechanical to electric drive, but electric drive has been around for decades. The DDG 1000 (Zumwalt-class destroyer) surface ship is also electric drive — so you have two very big important ships are moving to electric drive.”

Other innovations in the submarine program include an X-shaped stern to improve maneuverability and stealth, officials said. As subs evolved from using propellers to more quieter propulsors, they lost some surface maneuverability, they said. “With the X-stern, the Ohio Replacement will regain some of that maneuverability and, as a side effect, will have improved flow characteristics in the stern area while submerged,” the Navy expert said. “This will improve quieting and it simplifies the hydraulic control layout in the engine room.”

Similar to the current Ohio-class submarines, the replacements will be equipped to fire the Trident II nuclear missile, Breckenridge said. The missile, designated D5, has proven reliable in testing, with all but one of its 149 test shots successful, he said.

“Last week we did another round of successful firings of that missile,” he said. “The performance of that strategic missile is just incredible. As we look to deter bad behavior from other countries, we’ve got this kind of reliability.”

The new subs will eventually be fielded with the successor to the D5, Breckenridge said. The program office is also working with officials in the United Kingdom to engineer a common missile compartment. General Dynamics’ Electric Boat unit in Groton, Conn., is building prototypes under a $770 million contract.

The Ohio Replacement Program aims to control costs in part by borrowing technology already in production on the Virginia-class attack submarine program, officials said. Examples of the technology include conformal plane array sonar, fiber-optic links between sail-mounted cameras and a control room and “fly-by-wire” digital controls that allow crews to use a joystick and touch-panel to control the boat, they said.

Sonar technology is of particular importance to a submarine platform whose mission depends upon quietness and detectability, Breckenridge said. “The SSBN has to have a capable sonar system with hull arrays,” he said. “We also stream along a towed array by putting out a string of transducers that give you that much more listening power. SSBN wants to detect an undersea adversary – if we can hear them further than they can hear us we have a tactical advantage in the undersea domain.”

In addition, the new submarines are being engineered with a new nuclear-reactor core designed to power the ships for 42 years. Unlike the current Ohio-class SSBNs, which require a multi-year refueling process halfway through their service life, the new Ohio Replacement boats will be able to continue their missions without needing a refueling pause, Breckenridge said.

The technology also allows the Navy to conduct the same mission with fewer submarines, service officials and analysts said.
Tom Dougherty
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Re: Ohio Replacement Subs to Shift to Electric Drive

Postby JWLaRue » Mon Sep 30, 2013 1:57 pm

An X-tail boomer....that will be interesting!

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Re: Ohio Replacement Subs to Shift to Electric Drive

Postby ssn705 » Mon Sep 30, 2013 10:18 pm

Tom Dougherty wrote:Ohio Replacement Subs to Shift to Electric Drive

by Kris Osborn on September 27, 2013 DefenseTech

The U.S. Navy’s successors to Ohio-class submarines will feature an electric propulsion system, making them quieter and stealthier than today’s versions.



About damned time, but I also have to imagine that this is also a move to use ORP to develop a technology to be used in the replacement for VIRGINIA. Using VIRGINIA tech to bring down the cost of ORP should open the ability to push more money to electric drive. I am very excited by the possibility. Anything that further advances the force to ultimately increase the stealth and capabilities of our SSNs is fine by me.


Other innovations in the submarine program include an X-shaped stern to improve maneuverability and stealth, officials said. As subs evolved from using propellers to more quieter propulsors, they lost some surface maneuverability, they said. “With the X-stern, the Ohio Replacement will regain some of that maneuverability and, as a side effect, will have improved flow characteristics in the stern area while submerged,” the Navy expert said. “This will improve quieting and it simplifies the hydraulic control layout in the engine room.”



I have to disagree with this statement... I don't think the hydraulics will be any less complicated, in fact if they follow the newer method of having all four planes move independently you will double the hydraulic requirements. They may save something by not having split sternplanes, but it'll probably be a wash at best. As for the surface maneuverability piece, a boomer will still be a pig on the surface regardless...the true advantage of an X plane configuration is in the enhanced level of safety in high-speed submerged operations...

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Re: Ohio Replacement Subs to Shift to Electric Drive

Postby Tom Dougherty » Fri Oct 04, 2013 4:50 pm

ORP should open the ability to push more money to electric drive.


I believe this is an AC drive system. In the past, Rickover insisted in DC Motors for the two TED submarines Tullibee (SSN 597) and Glenard P. Lipscomb (SSN-685), which didn't scale well in terms of size of the installation. I also believe that the idea is to have a compact AC drive that will fit back in the mud tank, eliminating the need for a shaft seal. At one point, I thought that this was planned for later blocks of the Virginia class (along with a streamlined sail)
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Re: Ohio Replacement Subs to Shift to Electric Drive

Postby ssn705 » Fri Oct 04, 2013 7:31 pm

Definitely agree on AC, but I doubt it will be in the mud tank. Possible but not probable; we like doing maintenance on things too much...whether they need it or not. It was hard to wrap my head around an engine room with no motor generators; an engine room with no main engines would be wild. I think the hydrostatics of it might preclude the mud tank also.

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Re: Ohio Replacement Subs to Shift to Electric Drive

Postby SubICman » Fri Oct 04, 2013 8:38 pm

The electric drive is a great idea. But some of the other things to go with it I don't agree with. There was talk about shifting out all of the hydraulic valves systems for electric motors where feasible/possible. I think you are putting too much of a demand on the battery with that option. It won't go well for reduced electrical situations if every damn thing is electric!

Tim
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