USN diesel sub thought exercise

[covert_shores]

We all know that it's not going to happen, but if the USN did see the light what might the sub look like? Or rather, what could it look like?

Overall capabilities
Weapons choices
Single or double hull? (Serious)
Mission balance and inbuilt capabilities?
Radical thoughts?

Looking forward to the discussion. And pictures are better than words

 

[Grey Havoc]

One could always go back to the future for a starting point, in this case circa 1979:

[snip]

The Type 2000 SSK (referred to as 'Design 2000' in at least one source):

(h/t of to TinWing for the image)​

 

[covert_shores]

I suppose the 2015 equivilent would be the type-216 design

Impressive but would it fit USNs likrly requirements?

 

[eshelon]

Hmm, "external forward missile 'belt'". Interesting.
Any visualisation?

 

[sferrin]

We all know that it's not going to happen, but if the USN did see the light what might the sub look like? Or rather, what could it look like?

Overall capabilities
Weapons choices
Single or double hull? (Serious)
Mission balance and inbuilt capabilities?
Radical thoughts?

Looking forward to the discussion. And pictures are better than words

"See" what light? Do you honestly believe the USN is clueless when it comes to non-nuclear submarines?

 

[GTX]

I believe a modern USN SSK would be very similar to the RAN sub requirements/capabilities - both Collins class and its replacement. I'm not speaking about the exact designs but rather the requirements/specification/weapons fit etc.

 

[sferrin]

I believe a modern USN SSK would be very similar to the RAN sub requirements/capabilities - both Collins class and its replacement. I'm not speaking about the exact designs but rather the requirements/specification/weapons fit etc.

Yep. With all it's limitations as well.

 

[shedofdread]

It's probably significant that even with the RN's more modest budget (relative to the USN), we went all nuclear...

 

[covert_shores]

It's probably significant that even with the RN's more modest budget (relative to the USN), we went all nuclear...

i thought that it was because we were cash struck that we abandoned diesel subs. If we had a bigger defense budget we would have kept them. Per the Harriers etc, giving up a capability doesn't mean that it wasn't good to have it. When we went all-nuclear we massively reduced our operational footprint and, quantitively speaking, our capability. Of course AIP was a diagram in books at the time (Italian experiments aside).

 

[covert_shores]

"See" what light? Do you honestly believe the USN is clueless when it comes to non-nuclear submarines?

I don't think that anybody said that the USN is clueless. There is a section of the USN submarine officer community (and I expect the SOCCOM/NSW officer community) who would like to see the USN adopt AIP subs in addition to the SSNs/SSGNs. Very few if any would advocate a complete switch. They often cite the trials with the Swedish boat which reminds me of the X-Craft trials USN did after the war.

The history of the 'nuclear navy' goes back to a time when AIP was not a viable alternative (hydrogen peroxide went bang). And there were some very strong characters involved like Admiral Rickover. The considerations were partly political: any compromise on the number of nuclear boats was seen as an open door for the budget vultures in Washington D.C. to reduce the SSN the programs. And it wasn't just diesels that suffered, even Rickover's pet project the nuclear NR-1 was never commissioned as an operational unit in order to not steal a hull-number from the SSN program.

Today I think that the resistance to diesel boats is institutionally indoctrinated and to the extent that it's thought-out, more or less plays with the same fear that accepting them will dilute the SSN numbers and compromise the related infrastructure to build/maintain them. USN views on AIP are therefre partly defensive. And the US sub builders aren't motivated to change that.

But, AIP has shifted the arguments from an operational standpoint, which is where this hypothetical topic comes from. I don't think that the USN will adopt AIP boats, but if they did 'see the light' so to speak, what would/could those boats be like compared to SSNs and compared to AIP subs of other countries?


My initial thoughts are that AIP subs would primarily be tasked with littorals, which brings with it SF capabilities. The Ohio SSGNs and certain SSNs are the best SF platforms in the world, but an AIP with hangar would arguably be even better. Especially if it had dual hangars although I think one is more plausible. And also if a) the hangar was integral so always present like on Grayback b) part of the sub's primary mission so that it'd be available when the war starts <<this is a massive deal for SF and why they increasingly do not rely on subs.

I also think that cruise missile capabilities would be a given and emerging technologies suited to over-the-beach reach like UAVs and SDVs/UUVs would be standard.

Of course they'd be capable in open water, but that'd be SSN territory. These would be 'Littoral Combat Submarines' (ouch!!!). The USN designation would likely be SSP? Or APSSGP to go crazy with the multi-capability designation (AP = transport personnel? SS = sub , G for guided missiles (defacto only cruise missiles) and P suffix for AIP).

 

[covert_shores]

My general thinking is that in order to optimize for the littoral mission, plus USN's higher SF capabilities, the layout ought to be quite unusual.

It's 80m overall with outer hull beam of about 10m (inner hull max diameter about 9.5m)

The aft hull form is usual but similar to several SDVs (some not well known). And the tapered nose with fat section near stern is actually inspired by some hydrodynamic studies - I'm not an engineer and lack fluid dynamics software, but I suspect that the shape is more hydrodynamic than it might at first appear.

The double hull is a bit of a departure but:
a) allows cylindrical inner hull sections despite streamlined outer hull
b) allows a casing in order to accommodate diver lucks and wet storage sections
c) Plenty of space for air cylinders, ballast and sonar arrays

twin screws allows smaller diameter (less danger to SDV ops and allows the sub to bottom-out. The motors could also be less powerful and offer some redundancy. I considered moving the motors inboard to allow maintenance but then the props would not be steerable. Integral thrusters are a given anyway I guess.



Please rip it apart!!! ;D ;D ;D ;D

 

[Grey Havoc]

The third forward torpedo tube is reserved for 'swim out' UUVs and the like, if I'm reading the layout correctly?

 

[covert_shores]

Yes, that sort of thing. An argument could be made that torpedo rooms are (or will soon be) unnecessary but I think that they offer a utility and adaptability which makes them worth keeping, even with minimal tubes. The sub layout could easily be switched with flank TTs. In fact that might be a good idea.

Crudely re-arranged with four flank tubes. Bottom pair have impulsor. Length reduced to normal. Not sure I like this layout but it does make some sense.

The lack of an impulsor is more to enable a compact triangular layout and to reduce cost/complexity. The TTs are over-length (8m for the shorter one, 9m the other two) just to keep lots of options open.

 

[ouroboros]

SSPX changes in one direction would as follows;

I would extend the decking forward of the VLS to the sail, and house more forward external torpedo tubes in pop-up launchers, two rows of four launchers. Rearrange the area forward of the pressure hull but aft of the sonar to be focused on a central backbone tube, containing the original 2+1 torpedo tubes in a triangle arrangement within the backbone. Hang a six shooter style rotary hangar bay for 6x medium UUV, with dorsal and ventral doors (a permanent wet bay for UUV's or additional gear. Finish the bow up with a platypus lip to house sonar. If thruster tunnels are a given, then going steerable pods seems moot. There were design studies for a ducted contrarotating propeller design that basically is like a blisk ring hung on the outer mold line. Slip the ring motor unit over the SDV hangar and stern pressure hull area such that the duct outer wall aligns just a bit higher than the ships keel to allow bottoming out. Maybe rearrange the stern pressure hull "tail" into two tails, so you have a triangle tube stacking arrangement with the SDV hangar on top?

For a different direction,

Go with a U shaped pressure hull laid flat so there are two "tails" aft with a vertical open space. That vertical open space represents a module block area that can potentially be changed/refitted but usually left as is. The port pressure hull tail is shortened to accommodate the lockout chambers. The center aft section contains the hangar door. An SDV hangar and underslung accommodation tube would occupy 2 module "blocks" with the SDV hangar extending aft beyond the block boundary intruding into the hangar door space, the third block occupied by the VLS tube pair. For a more littoral attack boat, substitute the SDV blocks with more VLS tubes and insert a compact sphere chamber in the outer hangar door space. A UUV mothership might have a wet well for medium UUV's of two blocks aft, with a small repair lock stacked with a repair workspace in the forward block area. As for what happens forward of the U bend, depends on design considerations. You could go to an H layout with a forward block bay.

 

[sferrin]

I don't think that anybody said that the USN is clueless. There is a section of the USN submarine officer community (and I expect the SOCCOM/NSW officer community) who would like to see the USN adopt AIP subs in addition to the SSNs/SSGNs.

A "segment of the community" to support just about anything can be found. Doesn't really mean it's a viable idea (all things considered).

Very few if any would advocate a complete switch.

Problem is, to a politician, a sub is a sub. If we had the ability to build non-nuclear subs the pols would immediately start gutting the SSN force in favor of cheaper non-nuclear subs. Capability wouldn't even enter the equation. Slippery slope that most are savvy enough to want to avoid.

They often cite the trials with the Swedish boat which reminds me of the X-Craft trials USN did after the war.

And do you know how the Swedish boat got here?


(June 27, 2005) – The Swedish diesel-powered attack submarine HMS Gotland arrives in San Diego on a transport ship from Sweden.

That's right, they had to bring it here by ship. That kind of limitation isn't really compatible with USN needs.

The last USN diesel:

https://en.wikipedia.org/wiki/USS_Albacore_%28AGSS-569%29


[/quote][/quote]

 

[Arjen]

https://en.wikipedia.org/wiki/Barbel-class_submarine
Barbel (SS 580), Blueback (SS 581) and Bonefish (SS 582) were laid down and commissioned after Albacore.
<edit>
https://en.wikipedia.org/wiki/Sailfish-class_submarine
https://en.wikipedia.org/wiki/Grayback-class_submarine
https://en.wikipedia.org/wiki/USS_Darter_%28SS-576%29
So were Sailfish (SSR 572) and Salmon (SSR 573), Grayback (SSG 574) and Growler (SSG 577), Darter (SS 576).

All three Barbel-class submarines, Grayback and Darter remained in service after Albacore was decommissioned.

 

[ouroboros]

Out of curiosity, what's a rough estimate of shaft power for cruising to a patrol zone on diesel, versus max power, typically for subs in this class? Some of the rationale that played out into the SSGT design with gas turbines in the sail might apply.

Also, has there ever been serious design work on a buoyancy assisted propulsion design, AKA Slocum Glider, Steel Albatross style? Or is the littoral ConOps not providing enough depth to be useful? (though cruise to patrol may have enough depth). Tucking in those long fins is a bit of problem though.

https://en.wikipedia.org/wiki/Liberdade_class_underwater_glider

 

[Arjen]

They often cite the trials with the Swedish boat which reminds me of the X-Craft trials USN did after the war.

And do you know how the Swedish boat got here?That's right, they had to bring it here by ship. That kind of limitation isn't really compatible with USN needs.

The Gotland-class submarines are designed for use in the Baltic, which explains their limited endurance of 14 days and the need for transport by freighter.
Ocean-going submarines like the French Scorpène-class (which have AIP) and the Dutch Walrus-class (which have no AIP) have ranges in excess of 10,000 nautical miles enabling them to be deployed without freighters.
Range/endurance data from 'The Naval Institute's Guide to Combat Fleets of the World 2000-2001'.

 

[covert_shores]

Yes the transportation of the Gotland is an old cheap joke that should not be taken seriously. The sub was leased along with its crew and needed to go to the west coast, so it went the cheapest route with the crew on leave in Sweden I seem to recall. This was much cheaper than a crewed voyage. Simple. I think the contract only paid for the crew while they are actually in US.

 

[ouroboros]

Has there operationally been a fuel bladder/drop tank used with diesel subs post-war, for cruise or AIP range extension? There was that DCNS concept for AIP LOx drop tanks but that seemed a little too far out. Something like a dropable tail extenson that was neutrally buoyant might work. What kind of tricks are there for working in fuel bladders into ballast tank spaces, or aux oxygen bladders in the ballast tank compressed air cylinders?

If going for a secondary hull, is there much merit for acoustic shaping, such as the throwaway comment from Ben Rich regarding naval applications of faceted shaping for subs? Say some sort of trapezoidal cross section that might favor bottoming out to look like a mound?

 

[sferrin]

Yes the transportation of the Gotland is an old cheap joke that should not be taken seriously. The sub was leased along with its crew and needed to go to the west coast, so it went the cheapest route with the crew on leave in Sweden I seem to recall. This was much cheaper than a crewed voyage. Simple. I think the contract only paid for the crew while they are actually in US.

Which doesn't change the fact that if you have to deploy say, from the West Coast to Japan, the SSN is going to get there a hell of a lot quicker without the need for support ships to refuel from.

 

[ouroboros]

Yes the transportation of the Gotland is an old cheap joke that should not be taken seriously. The sub was leased along with its crew and needed to go to the west coast, so it went the cheapest route with the crew on leave in Sweden I seem to recall. This was much cheaper than a crewed voyage. Simple. I think the contract only paid for the crew while they are actually in US.

Which doesn't change the fact that if you have to deploy say, from the West Coast to Japan, the SSN is going to get there a hell of a lot quicker without the need for support ships to refuel from.

If so, doesn't that simply mean there's an operational need for Dockwise style heavy lift ships in Sealift command for ships with short legs, which includes subs? After all, there's those yacht transport well deck ships that have fairly regular schedules, so there's established operational experience. Though that would require a heavy lift ship that has adaptable and easy to use ship keel supports/movable walls/etc, rather than the typical welded steel cradle frames. Which implies potential users of a fast transit heavy lift ship need to have bilge keels or other underside shaping to ease handling?

 

[sferrin]

If so, doesn't that simply mean there's an operational need for Dockwise style heavy lift ships in Sealift command for ships with short legs, which includes subs?

No, it just means you'd need one to get a non-nuclear sub there.

 

[Arjen]

Only if it's a short-ranged one.

 

[covert_shores]

Re VLS - the Virginia Payload Tube aboard USS John Warner (SSN-785). The single outer tube with single door is much lighter than stressing each individual tube to crush depth. Since the missiles will only be launched from a relatively shallow depth, the inner tubes do not need to be so heavily built. It's also more versatile and I'd bet simpler to install or reload, plus the size of the inner tubes could be varied in future without major overhaul or dry-dock time(?).

I think that new-build subs, SSN or SSK, this type of feature should be a given.

 

[covert_shores]

Also, has there ever been serious design work on a buoyancy assisted propulsion design, AKA Slocum Glider, Iron Albatross style? Or is the littoral ConOps not providing enough depth to be useful? (though cruise to patrol may have enough depth). Tucking in those long fins is a bit of problem though.

Sloping sides with clean lines have been a trend in subs:

Astute also has a chined nose, but that feature can be traced back to HMS Dreadnought. And the Swedes coincidentally angled their submarine sails like that back to Sjöormen-class. So not conclusive, but a degree of angling seems plausible. Playing with unusual but not far-fetched ideas:

I think I prefer option a) as it has the lowest wetted surface area (lowest form drag) and minimizes weight.

The extra pop-out tubes is an interesting way to maximize weapons load but the tubes would have to be rated down to below the maximum operating depth, so quite heavy. Plus the implsor system. Add to that the weight of the missiles which, unlike torpedoes, would be significantly negatively buoyant, and we have a weight complication. Not unsolvable as the Soviets proved although their ECHO/JULIET cruise missile boats were all massively double-hulled with significant reserve buoyancy.

Another thought is whether the boat could be sail-less? Just a retractable fair-weather bridge over the main hatch like the latest dry-SDVs. Masts could retract fully into the hull and/or fold into the casing. This would mean that even if the sub had a 10m hll diameter, the overall height would be less than a small SSK.

 

[ouroboros]

Now I remember the why those ideas stuck in my head. Renegade 1 FSSN had the six shooter hangar and the ring drive, and the single hull Forward Pass concept had the ring drive with the aft hangar door and external weapons, and multihull Forward Pass was three parallel hulls, but amenable to a single U hull.

http://www.secretprojects.co.uk/forum/index.php/topic,6343.0/highlight,future+submarine.html

NNEMO predecessor/parallel to Forward Pass, better illustration a possible U hull

http://www.secretprojects.co.uk/forum/index.php/topic,9133.15.html

The CONFORM design had levered periscopes/masts that would sit flush to the hull in an upper slot.

http://www.secretprojects.co.uk/forum/index.php/topic,7792.0/highlight,submarine.html

Recent work on fiber optic periscopes with the eventual aim of making the periscope/sail a UUV of sorts have been floated around. Lasermotive makes fiber optic tethers that are capable of data and power delivery via high intensity laser light and a photovoltaic cell on the other end. The suggestion of a U pressure hull provides a convenient space for a vertically retracting mast/sail in the nook of the U.

There was also a soviet sailless design, but that was more about brute force solution to speed with a tadpole hull.

http://www.secretprojects.co.uk/forum/index.php/topic,9275.msg83980.html#msg83980


The angled coming/decking (resembling half a hex) is the easy way out, but reflections from the rounded hull below the waterline/halfway point down to the seabed are problematic, hence why I suggested a full trapezoid cross section (so the hull sends up looking more like a clothes iron or a horseshoe crab), though I guess a hexagon would work. Faceted shaping is all about pushing reflections where you want them go, so curves don't help. Ben Rich specifically pointed out the increased drag and lower top speed being an issue with a faceted design.

 

[covert_shores]

Fantastic links, had sent seen before or maybe forgot.

So taking a single-hulled boat with the reinforcing ribs inside the hull, and adding an incredibly thin wrap-around casing like 'b' above would be the ideal balance? Maybe a deeper keel approximately mirroring the upper casing? A bit like the U216 design actually.

I've started to doodle a refined layout taking into account the discussion. I wasn't keen on the pop-up tube concept but I've found that the upper casing has ample space for something along those lines. Not all the way along the back but two quite large 'lateral payload bays' in a shoulder position. Ordinarily these could be for small-diameter weapon tubes, UAV tubes or ROV hangars but they could be made just long enough for tomahawk tubes -maybe two or three per bay (it's weight I worry about). And the space is just large enough for wet carriage of an SDV, or even compact DDS ('suitcases') in a 'pop-out' configuration. They wouldn't be flush, more semi-recessed. That's problematic but not too far out and means that the boat could carry three SDVs without having to use the VLS as a hangar.


Sferrin, you are one of those dyed in the wool nuke guys? Or just Devils' advocate? If the ** real** fear is Washington politicians preferring cheaper subs, then there's no need to try to convince anyone that SSPs are less good at being SSNs than SSNs are. We all know that. But the reverse is also true. We don't hear you telling us that SSPs are not as good if you want to operate in the littorals, drop off SF close to a defended enemy port. Or use in policing missions like the Caribbean. Or export....

 

[ouroboros]

Fantastic links, had sent seen before or maybe forgot.

So taking a single-hulled boat with the reinforcing ribs inside the hull, and adding an incredibly thin wrap-around casing like 'b' above would be the ideal balance? Maybe a deeper keel approximately mirroring the upper casing? A bit like the U216 design actually.

I've started to doodle a refined layout taking into account the discussion. I wasn't keen on the pop-up tube concept but I've found that the upper casing has ample space for something along those lines. Not all the way along the back but two quite large 'lateral payload bays' in a shoulder position. Ordinarily these could be for small-diameter weapon tubes, UAV tubes or ROV hangars but they could be made just long enough for tomahawk tubes -maybe two or three per bay (it's weight I worry about). And the space is just large enough for wet carriage of an SDV, or even compact DDS ('suitcases') in a 'pop-out' configuration. They wouldn't be flush, more semi-recessed. That's problematic but not too far out and means that the boat could carry three SDVs without having to use the VLS as a hangar.

Option B isn't a hexagon though. Here's a terrible mspaint illustrating the extreme faceted trapezoid hull. Has a shovel nose bow, and a tapering stern but I couldn't draw that right. Though to be honest a hex secondary hull/coaming is the cheap and easy solution with conventional curved bows and sterns, as it's more ammenable to smooth hydrodynamics and less drag. A nuke boat can afford to blow power on a full faceted design, but a diesel boat has fuel cost concerns so drag is non-trivial.

The lower part of the picture is one thought on a pop-out weapons clip, the idea being you have a smooth 2D profile around the tube with a foil endcap plate and forward clamshell outer doors. The whole assembly rises out of the hull when you think you might need it, and only opening the forward clamshell outer doors when you fire. Though that does require the discipline to pop out rear launchers first in a multi row setup, in case they jam and can't retract, so you don't block the line of fire.


Probably the simplest arrangement for SSP ends up being the hexagon cross section, with an internal arrangement roughly like the singe hull Forward Pass design with the ring drive and coaxial UUV hangar lock, Virginia Payload Module like VLS tubes up front replacing the vertical clips, and a duckbill bow sonar array. Maybe a torpedo clip/sail hump like the Renegade 1 FSSN. The operational needs for UUV adjuncts determines whether the rear dry hangar area is large enough to hold all SDV/large UUV, or compress/reduce it and put that six shooter wet hangar up front ahead of the VLS tubes. The ugly issue is the SDV/UUV lock being roughly coaxial with the ring drive means you can't open the hangar/lock door and be feet dry easily, compared to you original design, which makes dockside loading more obnoxious.

 

[covert_shores]

So hexagonal with upper and lower casing but rounding of some corners is probably best. Which AIP best fits American considerations?

German style fuel-cell.
Good: high efficiency, low temperature.
Bad: special maintenance and infrastructure. Heavy.

French style MESMA
Good: operates at any depth. High power.
Bad: lower efficiency. Emission management?

Swedish style Stirling engine
Good: very established tech and easy to maintain. Comparatively low tech.
Bad: limited operating depth, takes up a lot of space.

Japanese style Li-Ion batteries (technically not AIP, just better batteries?)
Good: ??? U.S. Expertise already applied to SDVs. Considered safer to charge.
Bad: not confirmed on big subs.

German WW2 style hydrogen peroxide
Good + bad: blonde bombshell

Italian style stored O2+exhaust
Good: low tech
Bad: scalable? Ability to carry enough? Suited to direct drive of props?

Tea kettle nuke
Good: long endurance
Bad: ??

 

[ouroboros]

Battery tech continues to evolve, so increasing range every time you come in for a drydocking by swapping battery packs is interesting. If you are already using sealed batteries, what's stopping you from using externalized battery tubes stuffed into convenient spaces? Since your SSP is supposed to have precision thrusters and allow bottoming out, would a dropable but redockable keel battery sled/pod make any sense to improve range?

Tea kettle nuke, do you mean something approaching an RTG? That may be a more acceptable compromise for the USN but prevents export, since most RTG's are plutonium rich. I guess a sitrling style RTG is the most near term in terms of mostly COTS. Most small nuclear reactor work in the civilian space is looking at 50-100MW and are probably too tall. A thorium based MSR might be possible, but I have never seen a MSR in a longitudinal tube configuration, usually vertical to utilize natural circulation. Small Modular Reactor makers are chomping at the bit to get operational experience though, and military use is often cited as a path to get early operational experience without going through the NRC (though usually in the context of powering a base and not naval). An RTG alternative of sorts, the radiolytic chemical cell, currently at the early research level, is using beta radiation to generate electricity using surface plasmon forces and looks promising as that is direct electrical extraction (that isn't thermionic or thermophotovoltaic) and seems to have potentially good energy density.

http://www.nature.com/srep/2014/140611/srep05249/full/srep05249.html

Fuel cells invoke various issues, such as using LOx or air, using hydrogen or hydrocarbon fuels with a fuel reformer, closed loop or open, etc. From a logistics standpoint, air/diesel reforming seems simpler, followed by LOx/diesel reforming. Direct hydrogen storage is getting better (hydride based solid storage) but still finicky. DCNS floated the SMX-24 design, which used side fins to carry fuel cell LOx drop tanks (and battery pods?) externally like a fighter. For a closed loop LOx/H2 fuel cell system, ESA was reporting some good figures for spacecraft use.

http://www.esa-tec.eu/space-technologies/from-space/low-mass-compact-regenerative-fuel-cell-system-rfcs/

There has been research on interesting fuel cell/microturbine hybrid designs, where the fuel cell represents a combustor/topping cycle for a conventional turboshaft. RamGen, a company working on rotary ramjet throat based shockwave compressors, was involved with research into such hybrid fuel cell systems. Though to note, RamGen also is positioning themselves as a maker of a simplified single rotor rotary ramjet air breathing turboshaft, that gets diesel engine like SFC at gas turbine weights.

 

[covert_shores]

Evolving design with hex cross-section, subtle rounding at ends and flank payload bays (marked 'X' on the cross-section).

The casing further forward seems to be required for a ballast tank, although not sure where to take in the water for quick submergence. The pop-out thrusters in the upper casing are also limited for in-port steerage.

I still prefer the VPMs in that position instead of the nose.

 

[DrRansom]

Here's some food for thought:

Why go with AIP? The US Navy already has nuclear submarines to conduct long range patrols and missions. Adding AIP, because off it's long range, seems to be redundant.

Shouldn't the design prioritize weaknesses in US submarine fleet? Namely, high stealth submarine to conduct operations in littoral waters, with, presumably, bases in the near region.

If the sub is designed to operate in: Persian Gulf, Baltic, Black Sea, and First Island Chain, should that affect the choice of propulsion system?

 

[covert_shores]

Your point re littorals is absolutely right, which is the argument in favor of AIP vs nuclear for that operational need. And why the ideas being thrown around are heavy on SF capabilities (hangars etc) and strike.


AIP is also cheaper than nuclear which is, counterintuitively, why many in USN fear them.

 

[ouroboros]

Is that a twin skeg rudder/propulsor setup now? Why have a penetrating shaft though, nothing wrong with podded propulsors, even on a fixed skeg. Though that brings up an issue. If the fixed skegs are vertical, that won't work well with the hex cross section motive. Though that leads to the weird issue of if and how to implement an X stern, where the lower fins have the propulsor pods. Something like

\_____/
/\
/ \

due to the stern flat plate area being above the body centerline?

Also, tractor propeller rather than pusher if podded?

 

[covert_shores]

What are the maintenance implications of prodded motors? I like the idea of two smaller motors with modest diameter props, seems cheaper and added redundancy.

 

[DrRansom]

Your point re littorals is absolutely right, which is the argument in favor of AIP vs nuclear for that operational need. And why the ideas being thrown around are heavy on SF capabilities (hangars etc) and strike.

But, if the focus is littorals in confined waters, then shouldn't that be incorporated into the analysis of propulsion? A several thousand nautical mile AIP range is excessive when the need is for short ranged operations.

 

[gTg]

In the context of choosing the propulsion system, what do you think about the SU/RU concept of using motherships (Yankee / Delta Stretch) to bring the smaller subs to the deployment zone to do the actual job? Or would this be too close to the current SSGN/SDV setup?

 

[sferrin]

AIP is also cheaper than nuclear which is, counterintuitively, why many in USN fear them.

The USN doesn't "fear" AIPs. : They fear dumba$$ politicians who would think an AIP is a viable substitute (because they're cheaper), for ALL missions, for an SSN. If the USN knew it could get a few AIPs and not have the SSN fleet taken from them they'd probably be all over it.

 

[ouroboros]

The long AIP range may not necessarily be for long transit but simply longer time on station and longer AIP approach. If you can tolerate snorkeling, you should be able to get fairly near the patrol area before ASW assets spot the snorkel. SSGT subs are generally surface transit so the deployment area isn't as much of a secret (DCNS SMX-25 was the flip version, an antiship submersible frigate that can be a sub in a pinch).

http://www.secretprojects.co.uk/forum/index.php/topic,11460.msg108942.html#msg108942

Any kind of surface mothership like a heavylift ship would be an even worse giveaway unfortunately, and probably no faster than a SSGT. A nuclear sub transport mothership takes nuclear hulls away from the SSN fleet, and is an export non-starter.

An extreme solution could be a catamaran hulled cargo WIG with the sub hanging from the center airfoil might have the cargo capacity necessary to pull it off, assuming the trade went the other way and you shrunk the sub some as it can be short legged. Low altitude so the detection radius is more like a surface ship, but it can quickly slip in past an ASW/AWACS gap, drop off, and egress back out. Pickup might be more problematic. It would also be the largest WIG ever made, but the size works in favor of WIG ground effect scaling and wave height clearance considerations.