sure
shows some of this too. I'd say in the case of "single hull". There is still going to be significantly more space across the really noisy engine room area for noise isolation equipment than a double hull sub of same beam. I mean even the Russians have gone to single hull with Lada and possibly with Yasen. It's about time China does too.
Aft section is some form of double hulled in a "single hull" submarine because you need ballast tanks in that section to balance the ballast tanks in the front section. The difference of buoyancy between the two ballast tank sections control the pitch of the submarine. It takes the form of either the tapering cone with the shaft around it to be a completely ballast tank, which limits how you can silence the shaft, or the pressure hull has a waist to form the ballast tanks around it, in which case, does reduce the space in the engine room.
No. 6 is the aft ballast tank.
You want to put the shaft within the pressure hull but you have to waist it. This reduces the space in the engine room.
The more buoyancy you need, the larger your ballast tanks you are going to need, and that will inevitably completely engulf the pressure hull anyway. You want as much negative buoyancy in order to dive deeper and put as many thermal layers as possible from your attacker. If you don't have deep dive requirements, in a double hull, you can go with thinner ballast tanks anyway with lets you enlarge your pressure hull. Notice how the pressure hull covers both engine room and propeller shaft to the very end.
It becomes a matter of how deep you want to dive. The Soryu class is known to dive very deep, and so does the Yuan class. These requirements came about because there are sections in the East and South China Seas that are very deep and are trenchy.
The Lada class looks like this, which is typical of European SSKs.
The front is entirely a ballast tank, and the rear taper is a ballast tank wrapped around the shaft and the engine room. If you look at this, its still tight in the engine space. European SSKs also have shoulder hump that is a free flood area and can be used for hold things for the AIP like oxygen. In other designs, you still have a sectional double hull at the bottom to be used for fuel.
There is another reason why you might want to do a single hull design like this versus a double hull, and it comes from an entirely different vector. That is, the single hull design is likely less labor intensive to make. It looks simpler to construct than say this.
Single hull submarines use a greater proportion of capital intensive equipment (machine presses, etc,.) to form the partly hydrodynamic pressure hull, while the Soviet Union and the earlier PRC has less of such, but has more cheaper labor.
Double hulls are more labor intensive, but less capital intensive. You can design the pressure hull to be a much simpler cylinder form, which is easier to press, and the complex hydrodynamic form can be pressed with machinery available using thinner metal skin, so the presses don't need to be as powerful. You got the cheaper labor to weld the more complex setup altogether. But nowadays, modern China and Russia are becoming more capital intensive in their manufacturing and look to reduce labor. Hence they will end up in the same trajectory as the Western sphere did.
