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Great comments, Kell553! The student's names are on the cover sheet - no submariners among them.

The problems with the Virginia Tech SSG design fall into two basic areas: lack of realism and errors in the design process.

Most naval submarine design information (performance and engineering data and design rules) is classified or closely held and not available to students in non-Navy programs. Further, the open literature submarine design information that does exist is likely to represent older designs (not applicable to current designs) or be incorrect or, even more likely, incomplete. Hence, with no credible weight, space, and other data for military hardware, student-generated designs of notional US Navy submarines cannot be expected to be realistic.

So, while some lack of reality can be forgiven, engineering mistakes are a different matter. In addition to the previously mentioned use of surface ship VLS modules, some of the other design errors most significantly impacting the Virginia Tech SSG include:

- Selection of an all-double-hull ship with most of the between hull volume free flooded, an inefficient approach if you are looking to minimize ship size. The students then attributed buoyancy to this free-flooded volume, thus providing the design with more than 400 tons of non-existent displacement. Further, the weights are incomplete and underestimated and the weight accounting is inaccurate. So, between the overestimated displacement and underestimated weight, the "actual" SSG weighs many hundreds of tons more than it displaces and it will not float.

- The pressure hull diameter is too small for three platform decks and an adequate hold and the distance between the pressure hull and outer hull is too small for fabrication and maintenance.

- Lack of understanding of the selected hydrogen storage system led to over sizing the variable ballast system by 600 tons.

Overall, there seems to have been no "reality check" during the design process. For example, the SSG carries a C&C/combat system very close to that of Virginia and it has 24 internal VLS tubes. How can that be done in a ship half the displacement of Virginia and not much larger than Collins? It makes one wonder at the level of faculty oversight of student ship designs at Virginia Tech. This design went off in a very wrong direction early in the design process with no hope of recovery.

A feasible SSG that, for the most part, satisfied the design requirements (other than the cost cap) would be thousands of tons larger than the 3800-ton SSG design. At that point, an SSGN (with unlimited flank-speed submerged endurance) that satisfied the requirements (other than cost) would be a superior alternative even if more expensive.

WIWD wrote: I saw an SSK design produced by the USN MIT post grad course (dating back to 92 I think) an I believed it included a submariner. I don't know if it was driven by the parameters from the academic staff but it was a lot larger than an Upholder (ocean capable SSK) and deployed into theatre on a fast heavy lift ship. So much for stealth...

Student ship design projects are often deliberately set up to create limited-scope design problems and may not be very realistic. (Non-nukes are not suitable for the USN but student designs are all non-nuke.) In the MIT case, the lift ship appears to be an expedient to overcome the inherent long-distance transit limitations of non-nuclear submarines. As for stealth, if you are operating in, for example, Iranian waters, the submarine does not need to be particularly stealthy during its transit from Norfolk or Pearl Harbor to Diego Garcia or even closer to the Straits of Hormuz.

Splott wrote: Couldn't an old SSBN be converted to mother ship for the SSK? An Ohio class SSBN is 10 time larger than for example HMS Gotland!

A Trident sub couldn't surface with diesel boat on its deck. Would that be an acceptable constraint? Underwater towing might be a possibility though.

WarshipAdmin wrote: . . . I'd point out that that report is a reasonable effort, given that they are kids at uni. . . . and you should bear in mind that their course is not called naval architecture. In the real world they've still got a very long apprenticeship before they'd be doing that level of system design. Also you don't know how long they were given to do that project.

At the time, the SSG designers were Virginia Tech naval architecture students and the design was a senior year project performed over two semesters in conjunction with ship design courses. I agree that they did a hell of a lot of work, much of which was of high quality. It's just a shame that the major flaws in their design were not pointed to them by their faculty advisor. I suspect that the advisor was not aware of the flaws.

For westwords:

You are relentless in your quest for a very heavily armed non-nuke sub. You wrote:

Closed Cycle diesel is my choice for sustaining maximum speed for several hours or a couple days until the LOX supply runs out. . . .

According to Wikipedia (http://en.wikipedia.org/wiki/Air-independent_propulsion), a closed-cycle diesel AIP system is offered by Nordseewerke. However, all of the many existing AIP submarine types listed use other AIP methods. Do you know something that the others don't?

What seems to emerge is an AIP that is very quiet at patrol speed and could be powered by Stirling cycle engines and switching to the noisier diesels in closed cycle operation to feed the motor which might be capable of 25 knots for several hours.

This concept utilizes two different AIP plants! Anyway, it is my understanding that closed-cycle diesels are for low-speed endurance, as are other AIP systems, not for sprinting.

The battery in this case would be for times when husbanding the LOX supply was critical.

I think you have things backwards. The AIP plant keeps the sub going at slow speed for long periods of time while also keeping the battery fully charged for occasional short-time high-speed events such as chasing a target or evading counterattack. Open-cycle diesels are used for long-distance transits while surfaced or snorkeling.

As for weaponry, six tubes should be able to handle 36 reloads if arranged with the usual racks carrying 3-6-3 weapons across the torpedo room.

The number of weapons that can be stowed across a torpedo room is a function of hull diameter and, if angled tubes are used, the specific angle at which they are installed because space is required for the stowed weapons to pivot from their stow angle to the tube angle. So, there is no "usual" unless many classes of subs have the same hull diameter and torpedo tube arrangement.

Since we're on the topic of torpedo rooms and torpedo tubes, Virginia Tech's SSG arrangement is all wrong. The torpedo room appears to be too small to accommodate the stated payload. Torpedo tubes cannot be stacked three-high in a 7-foot high deck. The torpedo tube breech doors are not in the same vertical plane which will greatly complicate loading weapons. More of the torpedo tubes should be inside the pressure hull and the torpedo tube shutter doors should not be in the sonar dome.

. . . another displacement driver is the power required which in turns draws on the AIP system and that in turn would drive displacement up. I do not expect an SSGI to be small but neither do I believe that a Seawolf size hull is needed.

It is the endurance issue that will determine the ship size outcome. It is possible that the compounding problem of larger sub leading to a bigger propulsion plant requiring more fuel and LOX leading to an even larger sub, etc., will ultimately result in a completely outrageous design. The answer can only be found by actually performing some submarine concept design studies and comparing the results. In any case, for whose navy is this SSGI intended? (Remember my questions from a previous thread? Where is the sub based? Where will it operate? For how long will it be on station? . . . These are endurance related.)