Columbia-class SSBN (SSBN-X Future Follow-on Submarine)

Vepr157 said:
Then again, the Navy did bizarrely end up using the placeholder SSN 21 for the Seawolf class.
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Yeah, I have no idea what happened there. Can only assume that some idiot wrote the ships in class as SSN-21, -22, and -23 during procurement and they or their office was too important to correct to 774, 775, and 776.
 
Scott Kenny said:
Yeah, I have no idea what happened there. Can only assume that some idiot wrote the ships in class as SSN-21, -22, and -23 during procurement and they or their office was too important to correct to 774, 775, and 776.
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I think it was a matter of not wanting to explain why the Navy was "changing" from SSN-21 to SSN-774. And then it became clear that the Seawolf was going to be a short run, they were OK being very nonstandard. Same basic logic as DD-21 becoming DD(X) and then DDG-1000.
 
Scott Kenny said:
I don't think Centurion was ever proposed as a name for a ship in the class, though.
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So here is the story.

Centurion was the name of the submarine program that followed Seawolf. The new submarine for the next century, it would be smaller and cheaper than Seawolf. Centurion was going to be the name of the class and first boat as well. Congress found out about the program and got upset the Navy started a named submarine program without Congressional approval. The SHTF. So everyone working the project got a letter stating that we were no longer allowed to call it Centurion. It was to be called the New SSN design, or as everyone came to know it NSSN. NSSN was what the Virgina program was called until the first boat of the class was named.
 
eflight said:
So here is the story.

Centurion was the name of the submarine program that followed Seawolf. The new submarine for the next century, it would be smaller and cheaper than Seawolf. Centurion was going to be the name of the class and first boat as well. Congress found out about the program and got upset the Navy started a named submarine program without Congressional approval. The SHTF. So everyone working the project got a letter stating that we were no longer allowed to call it Centurion. It was to be called the New SSN design, or as everyone came to know it NSSN. NSSN was what the Virgina program was called until the first boat of the class was named.
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I stand corrected!

Thank you!
 
Scott Kenny said:
It gives somewhat better control in general conditions, but has issues at the extreme edges (full dive and hard rudder, as in evading a torpedo)
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The offset may be due to the specifics of how the planes are linked internally.

In the 688, the vertical planea and the horizontals are slightly offset as well, to allow their control yokes to clear each other. There may be some sort of similar cross-connection in the Columbia or some other interference issue that makes it too crowded to have them all in one plane.

https://www.globecomposite.com/blog/x-factor-columbia-class-submarine-design
 

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TomS said:
The offset may be due to the specifics of how the planes are linked internally.

In the 688, the vertical planea and the horizontals are slightly offset as well, to allow their control yokes to clear each other. There may be some sort of similar cross-connection in the Columbia or some other interference issue that makes it too crowded to have them all in one plane.

https://www.globecomposite.com/blog/x-factor-columbia-class-submarine-design
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As I understand it, the control yokes back in the stern look a lot like what @merriman builds in his RC subs (I didn't get to stick my head back there and look myself). So yeah, there usually needs to be an offset between the two planes for that. Even though you need to do some control mixing to get the boat moving the right way which means each leg of the X needs to move independently.
 
Yes, it is a result of opposing sets of planes being on common stocks, causing them to be offset longitudinally to prevent the stocks from intersecting. This offset is also present in a normal cruciform sterns (between the rudder and the stern planes), but it's harder to notice that the rudders and stern planes are offset due to their different shape.

See the below drawing of the Albacore.
 

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Scott Kenny said:
Even though you need to do some control mixing to get the boat moving the right way which means each leg of the X needs to move independently.
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I'm not sure you strictly do need each leg to move independently unless you're trying to get the boat to roll on its axis. Which is probably a good way to get yourself on an awful lot of people's naughty lists (though possibly not for very long) and also impossible with conventional control surfaces. I suspect that you could probably eliminate, or at least mitigate, the roll effect of the fin with independent planes.

You generally get more pitching moment, possibly less yaw moment depending on details, and drag while manoeuvring is increased as part of the work of one set of planes is cancelling out the other set.
 
Vepr157 said:
Yes, it is a result of opposing sets of planes being on common stocks, causing them to be offset longitudinally to prevent the stocks from intersecting. This offset is also present in a normal cruciform sterns (between the rudder and the stern planes), but it's harder to notice that the rudders and stern planes are offset due to their different shape.

See the below drawing of the Albacore.
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Fascinating.

You'd think with the need to adjust each plane individually they'd just install 4 hydraulic cylinders, one for each plane, and let the computer determine the best deflection for where you want to go.

Handy if one gets damaged externally or you need to fix something internally too.
 
jeffb said:
Fascinating.

You'd think with the need to adjust each plane individually they'd just install 4 hydraulic cylinders, one for each plane, and let the computer determine the best deflection for where you want to go.

Handy if one gets damaged externally or you need to fix something internally too.
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Well, that's the thing, you don't need to adjust the planes individually unless you need to induce a rolling moment (as @Yellow Palace mentioned above). Full yaw and pitch control is possible with just two sets of planes. The idea was that if one hydraulic cylinder jammed during a dive, the other set of planes could be moved to a position to surface the submarine, although you would have no control over course, so the submarine would spiral upward. Not ideal, but better than relying on a single hydraulic cylinder for a traditional cruciform stern. The only other option would be to have a second stern plane cylinder (as is the case for SSN 718, the Seawolf, Virginia, and Astute).

Having just two hydraulic cylinders greatly simplifies the system, both mechanically and "computationally" (in those days an electromechanical control system was used), halves the number of large hull penetrations, and saves a lot of space in the very tight confines of the stern cone. I also suspect the Albacore/Columbia arrangement is inherently more robust, as each stock is supported by two bearings on either side of the line shaft. Nevertheless, everyone else who has done X-sterns (the Germans, Japanese, French, and Dutch) appear to have done with four independent planes.
 
I think you could order combined pitch and yaw plane deflections with individual control but as you point out, greater simplicity and reliability of control yokes would probably trump that.
 
jeffb said:
I think you could order combined pitch and yaw plane deflections with individual control but as you point out, greater simplicity and reliability of control yokes would probably trump that.
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I'm not picturing how you can do that.

In my example of Full Rise and Full Rudder, you have two competing control directions that need to happen. For Rise, you need the upper two planes to both be trailing-edges inboard, lower two planes trailing edges outboard. For Rudder, all the planes need to be TEs inboard on one side and TEs outboard on the other side. To mix those two, you're either not going to get full travel for either Rise or Rudder, or the planes have more physical travel than the computer commands for "Full" travel without any split command.

This is assuming just 1 control surface per arm of the X. At least the horizontals of the late 688s were split, with each part of the split powered by a different ram and IIRC different hydraulic circuit.
 
Scott Kenny said:
I'm not picturing how you can do that.

In my example of Full Rise and Full Rudder, you have two competing control directions that need to happen. For Rise, you need the upper two planes to both be trailing-edges inboard, lower two planes trailing edges outboard. For Rudder, all the planes need to be TEs inboard on one side and TEs outboard on the other side. To mix those two, you're either not going to get full travel for either Rise or Rudder, or the planes have more physical travel than the computer commands for "Full" travel without any split command.

This is assuming just 1 control surface per arm of the X. At least the horizontals of the late 688s were split, with each part of the split powered by a different ram and IIRC different hydraulic circuit.
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Apparently that's one of the benefits of using an x-stern.

Screenshot_20250606_121910_Chrome.jpg Screenshot_20250606_121929_Chrome.jpg
 
jeffb said:
Apparently that's one of the benefits of using an x-stern.

View attachment 772489 View attachment 772490
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Again, you need to provide mixed signals to the planes with an X-stern because turns and dive need different control movements.

In non-extreme conditions, this gives better control, so better maneuverability.

It's in the extremes where the X runs into issues.
 
Scott Kenny said:
When you need both full dive and full rudder.

Such as when you're evading a torpedo.
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Do you need full dive and full rudder, or do you just need extreme movement? Because you can still put both sets of planes hard over, it's just that the combined effect will be a more extreme movement about one principal axis (either yaw or pitch) than a cruciform stern would allow.
 
Scott Kenny said:
When you need both full dive and full rudder.

Such as when you're evading a torpedo.
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Here is an excerpt from a Bureau of Ships memo titled, "Conversion of ALBACORE, Results of Conferences at (1) David Taylor Model Basin, 22 August 1957, and at (2) Bureau of Ships, 27 August 1957":
The X-stern is, at present, under consideration for the SSN, SCB Project 178 [what would eventually become the Tullibee]. The X-stern, particularly on bodies of revolution with a large length to diameter ratio, offers advantages in maneuverability. The plane rams are perpendicular to each other and offset 45° from the vertical and horizontal planes. All four surfaces are effective in maneuvers in both horizontal and vertical planes. Thus, if plane dimensions are the same as in the normal cruciform configuration, the X-stern produces a force 1.4 times that of the conventional planes (0.707 X 4 / 2 = 1.4) [note: cosine(45°)=0.707]. Since planes are at an angle of 45° with the horizontal, the span may be increased without exceeding the vertical projection of the maximum beam. The plane with the larger span has a greater aspect ratio and, thus, permits a further increase in maneuvering plane force and effectiveness. If, in a dive, one plane jams, the other plane may be actuated in the opposite direction to neutralize the effect of the jam. This ability, of course, increases operational safety and ability to regain control in the event of a stern plane casualty. The same recovery principle applies to surface turning in restricted waters. It is considered that an X-stern can be designed for ALBACORE which will not prejudice existing stability and maneuverability. As described above, it should provide increased operational safety. The counteraction of a jammed plane will produce motion in the other plane (counteracting a jammed plane in dive will cause the submarine to turn). This effect, although undesirable, may be acceptable.
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So in maneuvers in the horizontal or vertical planes in isolation, the X-stern produces forces 1.4 times that of a cruciform stern. In a turn and dive, the cruciform stern will produce 1.4 times the force of an X-stern. However, that is for submarines with identical control surfaces. Because the X-stern planes can have a higher aspect ratio, they can produce more force for a given amount of drag.

In practical terms, the hypothetical problem you mention is not a concern. The Albacore with the X-stern was almost too maneuverable, and various schemes were attempted to arrest her from a too-rapid maneuver (e.g., a B-47 parachute in the sail, dive brakes).
 
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Vepr157 said:
So in maneuvers in the horizontal or vertical planes in isolation, the X-stern produces forces 1.4 times that of a cruciform stern. In a turn and dive, the cruciform stern will produce 1.4 times the force of an X-stern. However, that is for submarines with identical control surfaces. Because the X-stern planes can have a higher aspect ratio, they can produce more force for a given amount of drag.
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There's a slight caveat in that while the horizontal planes and the lower rudder are limited to the diameter of the hull (approximately) by practical considerations, you can in principle make the upper rudder as tall as you like and get very large yaw moments.

Anyway, if we want to argue about submarine dynamics... where are the forward planes going?
 
Yellow Palace said:
There's a slight caveat in that while the horizontal planes and the lower rudder are limited to the diameter of the hull (approximately) by practical considerations, you can in principle make the upper rudder as tall as you like and get very large yaw moments.
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In principle, sure, although in practice that's not really an issue.
 
Yellow Palace said:
There's a slight caveat in that while the horizontal planes and the lower rudder are limited to the diameter of the hull (approximately) by practical considerations, you can in principle make the upper rudder as tall as you like and get very large yaw moments.
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Not really.

The horizontals on the Ohio-class are larger than the hull diameter by a bit (inboard of the stabilizer endplates, I mean), and IIRC the lower rudder is ~2-3ft deeper than the keel.

You could even make the horizontals on a sub as much wider than the hull as the diameter of the mooring camel floats, ~10ft or so.

Plus, a super tall rudder will induce a rolling force that then needs to be countered by something. Could be stabilizer endplates like on Ohios and 688s, could be anhedrals like on Seawolf and Virginia.


Yellow Palace said:
Anyway, if we want to argue about submarine dynamics... where are the forward planes going?
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IIRC, Albacore demonstrated that bow or fairwater planes are not required with an X stern, but I'd hope that the planes are going on the bow.

Planes on the fairwater/sail/fin mean that you need a good wave over them to get down, whether that's your initial dive or you broached accidentally and need to get back down in a hurry. Planes down low on the hull stay in the water and so are always working for you.
 
Scott Kenny said:
If I'm right and the SSN(X) is more or less a Seawolf front end grafted onto a Columbia engineroom, ~10ktons is about right.

The concept art certainly doesn't have any VLS amidships. I do kinda expect that there will be an SSGN(X), or rather a Columbia-class SSGN.
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Given how abysmal Columbia procurement is (12 boats x 16 tubes is nowhere near enough D5LE to be sufficient for just Russia, let alone with the PRC's nuclear breakout) a Columbia SSGN is (imo) about the worst use of a Columbia hull. I did the math a bit back and we need something like 24-36 boats to equal the Ohios. (24 for the current 14x20, 27 for 18x24, and 36 for the planned 24x24 Ohios).
 
whatismoo said:
Given how abysmal Columbia procurement is (12 boats x 16 tubes is nowhere near enough D5LE to be sufficient for just Russia, let alone with the PRC's nuclear breakout) a Columbia SSGN is (imo) about the worst use of a Columbia hull. I did the math a bit back and we need something like 24-36 boats to equal the Ohios. (24 for the current 14x20, 27 for 18x24, and 36 for the planned 24x24 Ohios).
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If there is any increase in Columbia numbers, it won’t be because of Russia. Proof of Jina massively increasing their strategic arsenal will be the reason.
Propulsion/quieting necessities lead to the decrease from 24 to 16 tubes, iirc.
 
whatismoo said:
Given how abysmal Columbia procurement is (12 boats x 16 tubes is nowhere near enough D5LE to be sufficient for just Russia, let alone with the PRC's nuclear breakout) a Columbia SSGN is (imo) about the worst use of a Columbia hull. I did the math a bit back and we need something like 24-36 boats to equal the Ohios. (24 for the current 14x20, 27 for 18x24, and 36 for the planned 24x24 Ohios).
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If they can modify Virginias with an 84 foot plug couldn’t they design later Columbias with another 2x quad pack?
 
When looking at numbers, keep in mind that you gain operational numbers since there's no refueling overhaul. This is the original logic for 12 boats taking the place of 14. I don't entirely understand where the large amount of non-refueling work that was typically done during ERO is going to fit, but folks smarter than presumably have a plan.

Adding significant length to a boat is non trivial task, because there's lots of associated impacts. For instance, there's a standard for surface reserve buoyancy as a function of overall displacement. I.e., the main ballast tanks need to provide x% of the total displacement. Increase the total displacement, and you also need to increase size of the MBTs somehow, or add extra tanks. Increasing the size isn't possible without major redesign of the existing hull structure, which defeats the purpose of preserving the existing design and production line. Both SSN-23 and blk V VACL accomplish this by additional tankage included in the inserted section, but this would be significantly harder to do adding a quad pack. There's lots of similar impacts elsewhere as well.
 
Having a larger number of Columbias with a smaller number of missile tubes is a more survivable sea-based deterrent.
 
bobbymike said:
If they can modify Virginias with an 84 foot plug couldn’t they design later Columbias with another 2x quad pack?
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I don't think that the Delta Pier drydock in Washington is long enough. Remember that Columbias are the same length as Ohios, just with 2/3rds the missile load. Each quad-pack is 25-30ft of added length.

Another possible issue is the reserve buoyancy/ballast tank capacity.


sdmuleman said:
When looking at numbers, keep in mind that you gain operational numbers since there's no refueling overhaul. This is the original logic for 12 boats taking the place of 14. I don't entirely understand where the large amount of non-refueling work that was typically done during ERO is going to fit, but folks smarter than presumably have a plan.
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Happens in the ~35 days between patrols.

Yes. Really. Takes both crews plus a hell of a lot of shipyard staff to do it all. More total man-hours than happen in a standard, 6-month-long selective refit availability, done in ~35 days.
 
Scott Kenny said:
If I'm right and the SSN(X) is more or less a Seawolf front end grafted onto a Columbia engineroom, ~10ktons is about right.

The concept art certainly doesn't have any VLS amidships. I do kinda expect that there will be an SSGN(X), or rather a Columbia-class SSGN.
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Thanks, expect your correct, though may be with Columbia's wider bean than Seawolf (43 vs 40 foot), giving approx 15% increase in volume, displacement could be slightly larger than ~10,000 tons, dependent on length chosen, first two Seawolfs were 353 feet 9,138 tons, the third Jimmy Carter they extended to 453 feet, 12,158 tons.
 
Scott Kenny said:
I don't think that the Delta Pier drydock in Washington is long enough. Remember that Columbias are the same length as Ohios, just with 2/3rds the missile load. Each quad-pack is 25-30ft of added length.

Another possible issue is the reserve buoyancy/ballast tank capacity.



Happens in the ~35 days between patrols.

Yes. Really. Takes both crews plus a hell of a lot of shipyard staff to do it all. More total man-hours than happen in a standard, 6-month-long selective refit availability, done in ~35 days.
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TRF-B (and presumably KB) are 751 ft. SSBN is 560 ft. The docks could certainly physically fit a longer boat, problem becomes the amount of additional space needed for things like shaft replacement. I suspect one could go up to 600 ft or so without significant impact, though it might limit ability to do a shaft and removing the bow dome at the same time (not that removing the dome is overly common).

Fully understand maintenance done during refits. However, Ohio plan has that and the multiple year refueling. Columbia presumably does the same refit schedule, but without the refueling, which means either there's less major maintenance needed, or even more work is going to need to get done in refits. Probably some of both.
 

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