Ohio Replacement Subs to Shift to Electric Drive

USS_Maine

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.

About the Author

Kris Osborn
Kris Osborn is the managing editor of Scout Warrior.
  • Lance

    Glad to see Ohio get the new tech added to them I dont see them going away or any new sub coming soon in this fiscal environment.

    • Kole

      $20 says this can fly for less money than the F-35.

      • Rest Pal

        “fly” or “fry”

        I’d say it will “fry” for less money than the F-35.

        The US simply doesn’t have the money to do electric-drive. The plan will be scrapped, after shelling out a few billions for nothing.

    • tiger

      Well not so fast, Lance. The POTUS is not a big nuclear force fan. Funding for a new Trident sub has many hurtles.

    • Moose

      The class IS going away, the article’s title is very poorly worded. The electric drive will show up in the class which replaces the Ohio class.

      • Musson

        Exactly. The electric drive will show up in the new PRIUS class submarines.

  • LesG007

    Let’s just keep the lid on this from R&D through production. We cannot afford to let the Chinese infiltrate our Contractors and steal our secrets, like most other programs have. This is our last step up in our weapons and delivery systems which they have not gotten away with all of our secrets. Cyber espionage is huge and more sensitive information is being stolen each and everyday. Like the old adage states…Loose lips sink ships. Instill this in every military branch like they used to, and this crap will STOP ASAP!!!

  • EW3

    Have to wonder about the magnetic signature that can be observed from the air over a sub with this type of propulsion.

  • Rage

    Ohio Replacement Program = NOT Ohio Class. Talk about bad titling. This has nothing to do with the existing boats at all.

  • orly?

    I’m curious if we can progress ballistic grade polymer fast enough to make ships/subs out of them.

    That should improve sound signature correct?

    • Rage

      Yes it removes the noise created by the reduction gearing normally required between a steam turbine and a screw. With electric drive the turbine can directly spin the generator, and then the motor for the shaft can run at a different speed. Nothing but silent wiring in between. Most diesel submarines already operate like this. So do some surface ships, a number of surface ships had partial electrical drive like the Type 23 frigate.

      The USN built two nuclear electric drive submarines before, USS Glenard P. Lipscomb and USS Tullibee. The downside was electrical drive cost more and weighed more, leading to slower speed. But speed isn’t a big deal in a Boomer, and the technology has gotten better since those hulls went in the water.

      Back in WW1 era a number of US battleships and carriers had turbo electric drive too, but it faded for the same reason, excessive weight vs possible speed.

      • platypusfriend

        We don’t use the term “boomer” anymore to refer to Tridents, which we simply call “Tridents”. Nor do we say “Ohio”, for some reason. It’s just “Trident”, if you care what actual bubbleheads say.

        You’re thinking of the “old boats”, which were known as boomers; a boomer is featured on the patrol pin, also known as the “boomer pin” (or an “idiot pin” if you have a gold one).

  • brownie

    China is building new nuke subs and missiles. These SSBNs will be patrolling in the Gulf of Mexico and Atlantic within 3-5 years. China has not the bogus 240 nukes advertised but between 1,200 (Russian intel) and 3,000 (Georgetown U. Study). China is building between 100-300 nukes per year of various designs. She just took delivery of 15 new turboprop strategic bombers.

    • Steve B.

      30-50 years more likely for their ballistic sub force patrolling the Gulf of Mexico ?. Did you actually type that ?. Do you know how ludicrous that is ?. Go look at a map. It’s about 20,000 miles from China to the Gulf via Cape Horn, cause there’s no way they are using the Panama Canal for this. That’s a month transit over and another month back and then how long on patrol – ? another month ?, before they run out of food ?. Maybe they could put into Cuba, yuk, yuk.

      And those bombers ?, the PLAF has 120 H6 (not prop aircraft) with a 3000 range and about 10 tankers. These H6’s can’t even reach Guam. What aircraft are you talking about ?.

    • Juuso

      Georgetown U. Study has been debunked years ago and so is “Russian intel” claim. http://blogs.fas.org/security/2011/12/chinanukes/ http://lewis.armscontrolwonk.com/archive/5460/yes

      There you have, some realistic studies about Chinese nuclear weapons.

      • Rest Pal

        FAS didn’t debunk GU’s study; it merely disagreed with the estimate and offered its own estimate and reasoning. The linked article admits no one knows exactly how many warheads China has.

        Both estimates may be inaccurate. The FAS has been wrong many times in the past.

        • blight_

          I wonder where FAS rested on Saddam and WMD…

          • Rest Pal

            FAS had claimed that Saddam had WMD – nuclear, chemical and biological. If memory serves me right, FAS had even accused Iraq of developing long range ballistic missiles. All proven wrong.

            FAS has little credibility as far as I’m concerned.

    • So what !

  • PolicyWonk

    None of the newer SSBN’s are being designated as replacements for the Ohio SSGN subclass, and the POTUS designated a pile-o-dough for the extension of the Virginia hulls to provide a similar capability.

    Lamentably, the GOP-led HoR voted the funding for the Virginia hull extension program down to ZERO dollars. Hence – this important capability looks like its going to be lost when the Ohio SSGN’s are decommissioned.

  • blight_

    Perhaps the next SSGN’ed submarine should also serve as a electric drive testbed? Let’s figure this out before the R&D is billed to SSBN-X and each submarine costs more than its weight of platinium and rare earth metals.

    • JCross

      Similar electric drives have been used in Commercial vessels and Naval craft for a many years. Out of all the R&D risk on the new subs, this is going to be pretty low risk. The only possible difficulty would be to try to hide it from MAD equipment. And that’s just a matter of shielding.

  • @blight the US NAVY operated a Electric drive nuclear sub in the 1970’s I think ,and the French have been using Electric drives on their sub’s for years. the only reason the US navy did not go with them was they where conservative and did not trust the technology.

    • S O

      Actually, the USN used steam-electric propulsion on battleships a hundred years ago already.

      They had either good, still hidden reasons to prefer a direct coupling (unlikely, as other navies did use the generator- electric motor combo) or they were simply doing it wrong.

      • Rage

        The issue was pretty simple. The electric drive submarines could not go faster then a CVN running flat out at a reasonable cost, the power plant was too heavy for the horsepower produced.. The next large class of submarine built meanwhile were the 688s, specifically intended to run with fast carrier groups to defend them from the growing threat of Soviet attack and missile submarines. Because of sprint and drift tactics needed for good sonar performance the SSN has to be a lot faster then the carrier for this to work.

        One might observe that all the Soviet attack submarines also used direct drive systems, so they could have the speed to engage fast surface warships and other fast subs.

        The original interest US in the electric subs was more focused on hunting down Soviet SSBNs, which like all SSBNs were not all that fast but were rapidly becoming quieter with the Delta boats. Escorting the fleet won over hunting boomers, though the 688s were still quieter then the subs before them. Just not as a quiet as they could have been.

  • Dfens

    If they’re smart they’ll make it a hybrid drive so they can run silently using the electric drive but have the full power of the steam turbine available to run if they really need to get somewhere fast.

  • Tad

    Nice. I wonder if it will be as quiet as, say, a Type 214 with AIP and fuel cells or if the reactor cooling system will still be a big giveaway.

  • Mystick

    I’m curious how exactly they’ll “tie the electric motor directly to the propeller shaft” without reduction gears. Electric motors of all kinds favor RPM. Especially those under a heavy load like moving a large amount of (relatively) viscous fluid at any given moment.

    IMO, one more thing to fail for propulsion in an emergency.

    • Mystick

      As an additional thought, I’m surprised they haven’t tried an impeller approach yet. That would further isolate noise from the props and help with cavitation.

      • Dfens

        An impeller? You mean like an automatic transmission? They use a steam turbine now. I suppose if they wanted they could use steam to drive a piston engine. That would lower the output RPM quite a bit, though it would cost a lot of friction. I don’t know that a nuclear reactor would care about a little friction more or less.

        • Mystick

          No an impeller instead of a prop. Think an inboard ducted fan.

          • sharkey

            I have seen a rough sketch of a jet drive with the impeller/propellor built inside of the hull. It’s coming.

          • dratomic888

            It was called the Red October. Oh wait that was just a movie/book/theoretical paper.
            By the way every 688 class sub had an electric motor for emergancies. The prototype electric drive sub design had the motor constructed directly on the propeller shaft so needed no drive gears

    • Kevin E Hoeschen

      They will use DC motors – motors that have very good speed control all the way from very slow to very fast. I am sure these motors will be in excess of 15,000 shaft HP

    • bum291

      They will not use a certain RPM or DC engines, they will use frequency converters. It’s reliable, easy to repair, doesn’t wear out, doesn’t need lubrication. They can run at any desired RPM, can stop and hit a required RPM in seconds.
      As an ex-military, now engineer, trust me: this is the best they can get.

      Getting rid of the gearbox is one LESS thing to fail.

      Of course, someone might choose a crappy system and that can cause problems (just took at the F-35 oxygen device)

  • Lee

    I am totally elated to finally see a subject where so much constructive information is passed out, instead of the usual dribble that we see so much of. Thank you one and all for your very informative comments.

    • Bill

      Great comment Lee
      We used to chase subs out of NAS Norfolk in 1950 with old WW II TBM’S with sonar buoys.VS 27. Would like to hear what Naval Air does now about the chase.

  • Dfens

    They could go further and expand the steam through a piston engine instead of a turbine and use the engine to turn the generator. That way there would be nothing whirring away at really high RPM. If they did that, the steam powered engine could work as a 2 stroke and develop twice the horsepower of the equivalent diesel burning engine. Since the reactor itself doesn’t make any noise, then they’d be at least as quiet as a diesel electric if not quieter, plus they’d be able to run long distances underwater and make their own air like they do now.

    • platypusfriend

      The reactor makes steam; steam is loud. I cross-qual’ed sonar… own ship’s noise is mostly steam.

  • Kenny

    FYI: the chinese have successfully attach a “star fish” to a U.S. sub to track it for a distance of a few hundred miles using the same tech as the whale tracker but quieter, it broadcasted a very tiny burst of signal of computer code! this meant U.S. sub is no longer invinsible! this occurance off the coast of Japan sometime! and it is not a magnitised device but some kind of suction that look very much like a sucker fish that is very small! I hope the U.S. Navy is aware of this! if not pass this to them asap. The source is not reliable, but the info is investigatable! the attachment was attached while the sub was not at home base.

  • sharkey

    Wow! What a lot of info to absorb and yet it’s not all that difficult to condense into what is coming next. First, propulsors give the boats great maneuverability. Then the EMF signal from the electric motors has been dealt with for years so not a problem. Boats will revert back to (almost diesel boats) but eliminating the diesel for a very quiet reactor instead. DBF now becomes NBF. As to secrecy let us hope that the company which put out a scale model of our Boomers in the 60’s doesn’t get access to data allowing them to do it again. AIPs are not quiet enough and are also limited duration so phooey to that technology. Finally, the new reactor technology has enough excess power to be used for future weapons (think of the Bush class CVN which has electric launchers and will carry rail guns. I don’t know much more but my experience tells me that we have a great submarine coming in the future.

  • Nice article however I would be interested in how the experience with the SSN-685 propulsion plant is being parlayed into a new design. Clearly the surface fleets experience with AC power conversation equipment and improved efficiencies are now viewed as doable in a submarine.

  • Steven Stevens

    Why would the Chinese bother to infiltrate? Just do like they did in Clinton’s time and give political donations to the DemoncRat Party. The DNC will hand-over the drawings and data and the American Sheeple will yawn and watch American Idol reruns.

  • The USS Glenard P. Lipscomb (SSN 685) was the US Navy�s second prototype design using a turbo-electric power plant similar to the USS Tullibee (SSN-597). The Glenard P. Lipscomb was generally similar to the SSN-637 Sturgeon class, apart from the use of submarine turbo-electric drive [TEDS] rather than the standard geared drive. Intended to test the potential advantages of this propulsion system for providing quieter submarine operations, the substantially larger and heavier machinery also resulted in slower speeds. Those disadvantages, along with reliability issues, led to the decision not to utilize this design on the follow-on SSN-688 Los Angeles class of submarines. Although serving as a test platform, the “Lipscomb Fish” was a fully combat-capable attack submarine.

    • JJJones

      The Lipscomb was commissioned in 1915. You don’t think in 100 years we might have better technology to resolve reliability and speed issues?

      • dratomic888

        Sorry, Lipscomb was commissioned 1973. but yes electrical drive has improved in the 40 years since then. Glenard P Lipscomb was BORN in 1915.

  • bum291

    It’s about time, this is the norm for new surface merchant vessels and has been for a while already, especially in “high-tech” vessels. Those subs ought to be.

  • Bill

    Being a Boatswain Mate I never served aboard subs, but I was on two sub tenders and I retired from NSSF New London OPS Department where I was on tugs that moored subs (they can’t get underway or dock without BM’s) so I know a little about what subs can do. But, for the media to release any information about the technology of our submarine fleet is irresponsible. The Chinese and other countries already do enough damage to our military through cyber spying we sure don’t need to whet their appetites by announcing new thecnology through the news media.

  • Wilderness voice

    We lack the will to use them why have them.

    • blight_

      You want to use nuclear weapons?

      Guess it’s good the Soviets also “lack[ed] the will to use them” during the Cold War. Whew!

  • sharkey

    Just want to state that way the system of a motor driving the propeller shaft works is this: The shaft is wrapped and becomes the rotor. The stator is stationary with the shaft going through it. There is no clutch used to couple the motor for drive but it can be decoupled from the propeller. Not sure of this arrangement. It is a DC motor so can be fine tuned as to the number of revolutions (speed control). As someone stated the torque varies with the voltage applied but there are new materials and controllers now which can use DC much more efficiently. If you want to see an actual submarine with such a system, google the USS Dolphin which is on display at the Maritime Museum in San Diego.

  • Jack – DGI – AIS
    • sharkey

      Jack. Can’t cut and paste as the address is two lines. I will try to type it out.

    • orly?

      Says nothing about submarines, as it is incapable of such.

      FYI, this seems like a navigational GPS displaying all surface vessels in proximity trying to replace Furuno.

  • Max

    Whatever happened to MHD drives for subs? When I was in the Navy (80’s), the Soviets were rumored to have it. The fictional “Red October” had it, but was it fictional or not?

    • sharkey

      MHD in theory, uses one field of materials to electrically influence a second field of materials. As water, even seawater, does not have a ferrous material to influence, no motor (Stator) can influence the rotor because it is water and not ferrous material. There is one way to build a MHD which I referred to above. Jet drive. In other words: build a tunnel through which water can enter forward and exit aft but all built inside the hull. Put an impeller or propellor INSIDE but OUTSIDE the pressure hull but inside the tunnel and put a stator around the tunnel INSIDE of the pressure hull. Now put a voltage (AC) to the stator and it should start turning the impeller inside. This is a JET DRIVE. The benefit is that the stator is around the tunnel while the impeller is inside, separated by the PRESSURE HULL.

  • blight_
  • davec

    In regard to electric drive, didn’ the Lexington (CV2) and Saratoga (CV3) have electric drive when they were built back in the 1920’s?

  • Seems like this makes perfect sense as electric drive would significantly reduce radiated noise. Hardly a secret technology also.

  • Reading through the post and the comments as well makes me think that i think media or journalists must have a little of etiquette and limitations. They might be allowed to search for something to report but I think it must undergo screening and evaluation of their reports especially if it harms the security of the country. I mean they would still have that freedom but they must also think of how to save and help the country through responsible selection of reports. I guess we already know what’s helping us and what’s not for the benefit of the many people and the country itself.

    On the other hand, I was wondering how does it feel to ride in a sub?

    • sharkey

      Depends on the sub. An old diesel boat moving slow gives little to no feeling of motion. When it moves faster, say 7-10 knots it vibrates more but still is a stable platform. When an old boat turns at speed the sail tended to tip the boat so it leaned to the outside of the turn ie turning left the sail tipped to the right while a left turn did the opposite due to water pressure on the sail. Nukes and diesel both were stable until a maneuver caused pressure on the sail to do as above until they developed the Fairwater Planes. These planes were mounted up on the sides of the sail so the boat could turn and the planes would help to keep the deck under you tilting into the turn. They are gone now as the X configuration aft can offset the tilt. Bow planes are back on the bow and there are no Fairweather planes. Riding in a new nuke can get hairy though as the speeds at which they can maneuver can put the deck below you at rather drastic angles especially in a deep dive down or emergency surface maneuver up.

  • steve

    look at brit type 45 destroyer and new carrier class.
    all electric propulsion

  • Jason

    I was an A -ganger on the Hawkbill and in a sense the boats are somewhat of a hybrid in the first place you can ether run power from the diesel gen to the battery to the aux electric motor . or run the turbo generators to the battery to the aux electric motor. running on the battery is by far the quietest mode of operation. the bad part is that if you have to get out of dodge in a hurry, your screwed.

  • Phil

    Wow! Using electric engines to run submarines!? They say it’s been around for 50 years? Electric propellers were already in use when WWII began in 1939, which was 76 years ago.

  • Brian B. Mulholland

    davec, they did. So did the South Dakota battleships of WW II vintage; I believe a couple of older battleships, built between the wars, did so as well.

    • blight_

      I wish I knew why turbo-electric was killed early. The BB’s that had it would be New Mexico, Tennessee, Colorado classes; along with the Lexingtons laid down as battlecruisers. These classes were commissioned after the Naval Treaty, whereas the North Carolina was probably the first new-build treaty battleship (construction beginning 1937). I wonder what happened between the 1910’s and 1937 that resulted in going back to old technology? Did a supplier go bankrupt, or perhaps geared turbines outpaced turbo-electric, or turbo-electric was less mature/less robust?

      Might the changeover have been due to weight, or perhaps volume constraints imposed by weight constraints imposed by the treaty?

      Looking up the New Mexico class (which was completed in geared turbine and a turbo electric version) on the horrible Wikipedia:

      “A comparison of the turbo-electric propulsion with the more conventional direct-drive turbine design used on her sister ships showed that the conventional design generated 2.5x the power per ton of machinery and required 1/3 the floor area although at the cost of 20% greater fuel consumption, always a concern for the U.S. Navy given Pacific distances. The turbo-electric design allowed for the equipment to be split between smaller watertight compartments, which was a potential benefit should parts of the engine space be attacked and flooded. There was a design weakness in that all electrical connections went through a single switch room, which could entirely disable the ship were that room to be hit. Saratoga, which used a similar propulsion design, lost power for five minutes when it was hit by a torpedo in 1942. The scheme of watertight subdivisions was further weakened by large ventilation trunks passing through bulkheads and glass windows in the generator room bulkhead.”

      More power and less floor area would have been a powerful constraint for a treaty battleship. This probably explains the demise of turbo-electric until now.

      Also, (under the Lexington article in the same)

      “One advantage of turbo-electric drive was that the substitution of flexible electric cables for bulky steam-lines allowed the motors to be mounted further to the stern of the ship; this reduced vibration and weight by shortening the propeller shafts. Another was the ability to go astern at full power without needing a separate reverse turbine to do so, simply by reversing the electrical polarity of the motors. Other benefits were the ability to operate all four propellers if one of the turbo generators failed, and the possibility of operating only some of the generators at low speed with suitably higher loading and greater efficiency. “[Turbo-electric drive] was efficient, rugged and always reliable. But it was also heavy, intricate, and not easy to maintain and keep tuned up.” The machinery also required special ventilation measures to dissipate heat and to keep out any salt air. Even with this and elaborate insulation measures, protection from moisture or from flooding due to battle damage or other causes remained problematic and it posed the danger of high voltage to the crew if damaged.”