Alternate submarine designs: Cargo sub, Tanker, etc.

[seadude]

If a war ever happened, replenishment ships would be near the top of the list for enemies to sink. Destroy the adversaries capability to resupply and your enemy loses the capability to continue the fight due to lack of gas, water, ammo, food, etc.
Replenishment ships are slow, limited defensive armament or none at all, and are just plain sitting ducks.
What if existing or new submarines could be built as replenishment vessels instead with the capability to carry oil and other assorted cargo? They'd be harder to find and destroy since they're underwater. Only time they'd have to surface is for replenishing another ship. What do you think?

[zenrat]

How fast can a submerged missile sub (for example) go?

[Weaver]

The Germans had cargo submarines in WWI:

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


The Italians had several classes in WWII:

https://en.wikipedia.org/wiki/Italian_R-class_submarine
https://en.wikipedia.org/wiki/Italian_submarine_Barbarigo
https://en.wikipedia.org/wiki/Italian_submarine_Luigi_Torelli


A proposal to convert Typhoon class SSBNs has been made in Russia:

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


General article on cargo subs:

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

How fast can a submerged missile sub (for example) go?

About 30 knots plus change flat out, though they're pretty noisy and easy to detect at that speed. I don't know for sure, but continuous running at those speeds might eat the prop pretty quickly too, since they're designed to be efficient and quiet at much lower speeds.

[jcf]

SARO P.212

[scooter]

I used the Ohio as a nuclear-powered milchkuh for a squadron of fleet boats heading off to fight the 2d Korean War in a story.

[zenrat]

How fast can a submerged missile sub (for example) go?

About 30 knots plus change flat out, though they're pretty noisy and easy to detect at that speed. I don't know for sure, but continuous running at those speeds might eat the prop pretty quickly too, since they're designed to be efficient and quiet at much lower speeds.

Thanks H.  I should really have goggled that but i'm bone idle.
As I mentioned recently in another thread, in Against a Dark Background Iain M Banks has a multi hulled assault sub which runs up the beach, detaches the pressure hull with the troops in and then backs off leaving it behind.

[Weaver]

Some interesting issues to be addessed with bulk cargo in submarines would be:

1. Buoyancy.

Cargoes with a very high or very low density might seriously affect the sub's ability to submerge, unless it's ballast tanks were in proportion to the size of the cargo hold. In mitigation, as the Deutchland demonstrated, some insensitive cargoes (rubber in it's case) could travel inside the ballast tanks.


2. Loading and unloading.

Note how small the Saro project's hatches are in relation to it's cargo bay: pressure vessels generally don't like having big holes cut in them. The submarine freighter would be ideal for liquid cargo, or bulk cargo that comes in small indivisible units (grain, for example) but it would struggle with things like manufactured goods: how far do you want to dismantle a truck to get it in? What if there's an undismantleable too-large component that (tank hull?) that just won't fit through a hatch?

The biggest hatches in pressure vessels that I can think of off-hand are the hangar doors on I-400 submarines, where the whole hemispherical end-cap hinges open. That raises an interesting possibility: what about a triple pressure vessel design (like the Dutch Dolfijn class) with the machinery and ballast tanks in the lower two hulls and the cargo in the top hull with end-cap loading from each end and the control room in the middle?

Alternatively, how about towing a cargo "pod" behind an exisiting or adapted submarine? It's been looked at long ago and rejected because of control issues, but modern sensors and computers should be able to sort that out. It would need ballast tanks down either side and a really strong towing attachment, but it should be feasible. For laoding and unloading, it could be surfaced and then towed into a shallow dry-dock or elevating cradle by a normal tug boat. it would be particularly suitable for the Russian style subs with twin props.

[NARSES2]

I had absolutely no idea about that Saro project, thanks Jon 

[Hobbes]

How fast can a submerged missile sub (for example) go?

SSNs can reach 30+ knots, SSBNs are a bit slower (the Ohio class is reported as 25kn).

[jcf]

The SARO design was intended as a bulk ore carrier to operate between Diana Bay in Northern Quebec and the UK.
Top speed was to be 25.5 kts.

The submarine concept was considered to allow year-round ore transport.

[Weaver]

Going back to Seadude's original post, the strategic problem would be vessel size. Even the biggest subs ever built are still way smaller than most cargo vessels, so you've either need very big subs or an awful lot of them.

Very big subs are problematic for handling reasons, since the band of ocean in which subs operate is relatively shallow, and with very big subs you can reach a point where their crush depth is only a small multiple of their length, so if they lose pitch control (a common accident), their bow can reach a dangerous depth before the crew can react. the solutions are either travel slower or build the hulls much tougher to withstand a crash dive (expensive). The principal reason why nuclear boats quickly evolved stronger hulls and deeper diving limits wasn't because the greater depths were tactically useful, it was because their greatly increased speed meant that they would go much deeper in a crash dive before they recovered.

Building more subs than you have cargo vessels (because the former are smaller) would be vastly expensive and very slow, because the submarine business uses facilities and skill sets that are fairly unique and therefore difficult to ramp up quickly. People who can weld pressure vessels today are like the skilled machinists who were the peroduction bottleneck in WWII: if it takes three years to train one, then it takes three years, and no amount of money thrown at the problem can change that.

[scooter]

Very big suns are problematic for handling reasons, since the band of ocean in which sunbs operate is relatively shallow, and with very big subs you can reach a point where their crush depth is only a small multiple of their length, so if they lose pitch control (a common accident), their bow can reach a dangerous depth before the crew can react.

Which was a big problem with the I-400 boats.  They were 400' long, with a test depth of 330'.  In a crash dive, their stern was still above water, while the bows were heading into crush range

[Zombolt]

Is this thread confined to WW2?

Because I remember in Ace Combat 5, You had to hit a supply Sub as it was replenishing a Sub Aircraft Carrier. Some say it's based off the Typhoon class, though it is replenishing a Sub the size of a supercarrier...

[Weaver]

Very big suns are problematic for handling reasons, since the band of ocean in which sunbs operate is relatively shallow, and with very big subs you can reach a point where their crush depth is only a small multiple of their length, so if they lose pitch control (a common accident), their bow can reach a dangerous depth before the crew can react.

Which was a big problem with the I-400 boats.  They were 400' long, with a test depth of 330'.  In a crash dive, their stern was still above water, while the bows were heading into crush range

Especially with WWII hull forms, which were basically "sinkable boats" rather than "underwater flying machines". Their pitch stability wasn't good at all. Fun fact: when the USN adopted the body-of-rotation hull form, first tested in the Albacore and thereafter known as the "Albacore Hull", the designers were directly inspired by airship design and took airship aerodynamic research as their jumping off point.

[ysi_maniac]

Reaching the limits of submarine.

Submarine Battleship. in a certain way it could be like a 'BIG' Surcouf https://en.wikipedia.org/wiki/French_submarine_Surcouf

Submarine Aircraft Carrier.