SSBNX - Ohio Replacement

[DirtyFred]

Slated to serve through 2085, the Ohio Replacement program, the nuclear submarine is scheduled to begin construction by 2021. Requirements work, technical specifications and early prototyping have already been underway at General Dynamics Electric Boat.

Designed to be 560-feet–long and house 16 Trident II D5 missiles fired from 44-foot-long missile tubes, Ohio Replacement submarines will be engineered as a stealthy, high-tech nuclear deterrent.





Detailed design for the first Ohio Replacement Program is slated for 2017.

btw The Virginia-class attack submarine inventory will drop to 41 in 2029, according to the Navy’s recently released 2016 30-year shipbuilding plan. Ultimately, the plan calls for a fleet of 50 Virginia-class submarines by the mid-2040s.

[mikmykWS]

Can any of our submarine guru's explain the benefit of shrouded propellers?

Mike

[Casinn]

Wikipedia says a decelerating duct lowers noise levels. I always assumed the opposite.

http://en.wikipedia.org/wiki/Ducted_propeller

[STKS]

Wouldn't call myself a guru, but a pump jet means that the water around the propeller is kept at a higher pressure than the surrounding sea (sort of like a jet engine). The higher water pressure makes it harder for bubbles to form, so you get a higher speed before cavitation starts. There's also the bonus of the physical barrier between a noise source and the surrounding ocean.

[NakedWeasel]

I always thought there was a speed/power/efficiency benefit as well. I mean, they've been used in high speed watercraft for decades, right? Many modern, advanced torpedoes use them too, I think. According to wiki... ( https://en.wikipedia.org/wiki/Pump-jet )

Advantages:
Pump jets have some advantages over bare propellers for certain applications, usually related to requirements for high-speed or shallow-draft operations. These include:

*Higher speed before the onset of cavitation, because of the raised internal dynamic pressure
*High power density (with respect to volume) of both the propulsor and the prime mover (because a smaller, higher-speed unit can be used)
*Protection of the rotating element, making operation safer around swimmers and aquatic life
*Improved shallow-water operations, because only the inlet needs to be submerged
*Increased maneuverability, by adding a steerable nozzle to create vectored thrust
*Noise reduction, resulting in a low sonar signature; this particular system has little in common with other pump-jet propulsors and is also known as "shrouded propeller configuration";[2] applications:
Warships designed for low observability, for example the Swedish Visby-class corvette.
Submarines, for example the Royal Navy Trafalgar class and Astute class, the US Navy Seawolf class and Virginia class, the French Navy Triomphant class and Barracuda class, and the Russian Navy Borei class.
Modern torpedoes, such as the Spearfish, the Mk 48 and Mk 50 weapons.

Disadvantages:
*Can be less efficient than a propeller at low speed
*More expensive
*The intake grill can become clogged with debris; e.g., seaweed. The effects of this can be mitigated by having a reversing gearbox between the engine and the water jet.

[thewood1]

From a mechanical standpoint, I thought they also create more mechanical stress on the shaft and machinery.

[BradOrbital]

Yeah more objects to break.

[LoBlo]

If its not broke, don't fix it. Probably the most important aspects of the next gen SSBN are to reduce the manning and operating cost of the subs without reducing current capability. Leveraging off ongoing tech from the Virginia class is smart cost saving.

As far as the X-stern. Don't see much of an advantage for a SSBN hull. Its not a brown water vessel so the shallow water maneuverability isn't a needed operational capability. Just adds more complexity to the aft which equals less reliability, less robustness, and more difficult maintenance. The electric drive is interesting, but entails technology risk now since its going to be unproven tech in its current form. Previous sub electric drives of the 1970-1980s were lower energy while today's techniques are attempting to use either highly magnetic permanent magnets, which require shielding to disguise their magnetic signatures, or cryo-temps which requires low temperate cooling machinery onboard the engineer room, in order to increase energy output and reduced footprint. Advantages are that it circumvents the extreme tolerances needed to make a super-quiet direct drive transmissions, so it may overall prove cheaper and with lower maintenance than direct drive, only time will tell and the general public will likely never really know. If anything the size of the SSBN will give the engineers more room to work with than the SSNs hulls for their designs.

As far as the shrouded propeller. I'm not a guru, but a lifelong sub enthusiast. Non-shrouded props have water 'spilling' over the edges of the blades as the blade turns pushing the water radially rather than axially and wasting energy. Additionally its the edges of the the blades than have the tendency to form cavitation bubbles. Putting a shroud (first experimented with by the British SSN designers) alleviates both these problems by eliminating 'spillage' as well as increasing the pressure at the blade tips to mitigate cavitation and increase the subs 'silent' speed. The disadvantage is more weight at the stern and more complex design, fabrication, and maintenance. (ie more expensive and harder to fix).

[LoBlo]

Oh, and the 2nd poster above is interesting. It forgoes the X-stern, but adds but looks like hypothetical "drive pods" on the stern. It also includes the Virginia style high frequency array, which in reality will not likely be the case for 1) the bow diameter of the SSBN would allow this array to be housed hydrodynamically in the hull rather than the un-hydrodynamic flare the Virginia was forced to adopted because of the size constraints and 2) again this is not a brown water vessel so bottom mapping isn't a part of its operational repertoire.

[xavierv]

I talked about it in my Sea Air Space 2015 coverage (it was a couple weeks ago). Here is picture of the latest model

GDEB Unveils New Ohio Replacement (SSBN-X) Detailed Model at Sea-Air-Space 2015 Exposition

http://www.navyrecognition.com/index.ph ... ew&id=2608

Interesting thing going on at the back.

They will be huge subs (the Virginia is at the same scale...)