Also Planeman what's the point of having two pressurized hulls?
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Let me continue some of my thoughts on this matter. Evaluation of the Songs and the Yuans against the "ideal". How far are the Songs and the Yuans from the "ideal' PLAN conventional?
I dont' really know much about the design history of the Song class, so far it has not been revealed though one day, it will be so for the sake of posterity like other Chinese projects. I believe the roots of it though, lie sometime before the events of Tianamen Square, where China had a rosy military relationship with the West. There has been great French, German and British inspiration that migrated to a military that had been educated and grown up living on Soviet concepts. The design of the Song looked towards Europe, and with its single hull and squared bow, probably to the German Type 209s, British Upholders, and French Agostas rather than the Mings. This is the time period where the French had its greatest and still lingering impact on modern Chinese naval thought, ranging from the importation and copy of the Exocet that would lead to the YJ series of antiship missiles, to the various sonars (DUBV-23 bow sonars, DUBV-43 TAS, DUUX-5 flank sonars among them) that were imported, the Croatales that would become the HQ-7s, to the TAVITAC centers that would lay the basis for future combat centers in PLAN ships. Other influences range from naval radars, the turbine electric drive reported alleged to the 093, to the Lafayette like concepts that would lead to the 054.
However, the Song, which first came out 1995, was beset by unsatisfactory results. The next iteration came out in 2000, followed by one sub each year until 2004. This second period, where 3 subs are only built, suggest problems still existed and are being incrementally corrected with each later sub. Then sometime in 2004, when the third version of the Song came out, the PLAN finally hit the home run, opening the flood gates for mass production and this became the definitive Song version.
In that sense, the Song actually parallels another project, the JH-7. Initially the concept was good, but development problems and delays meant that the final product, when perfected, has become a bit dated and obsolete. I don't think the Song has the hydrodynamic refinements like you see in the Type 212/214 or the latest Scorpenes.
Conceptually obsolete or not, once done however, it appears to be a credible performer. Many conventional are what one would call coastal submarines, with surface displacements under 2000mt and are mainly meant to defend the coast and littoral waters. The Song sits in the spot between 2000 to 2500mt, indicating it has intentions to go farther out into the ocean, a true brown water submarine with some ocean going capability. For sensors, the sub appears to have low frequency flank sonars, which are are a luxury even in many conventionals around the world. Passive low frequency sonars have a greater detection range than MF or HF sonars, and this makes it vital for submarine vs. submarine combat. For passive LF sonar to be effective, the sub has to be quiet enough. Sound reduction measures, now considered standard around the world, include rubber tiling and a single shaft slow turning high torque 7 bladed asymmetrical skewed propeller.
The Song has a large sail for a submarine of its size, and you don't need a sail larger than what you need. Sails add drag and noise. Though, the Song may have a large sail because it needs it. There appears to be a number of sensors attached to the sail, including a turning navigation radar array. The sail also packs a surprise of its own, holes for which a QW series SAM can shoot through.
Videos from CCTV showed the Song having a modern digital combat center. This indicates that the sub has an ample power supply to run such equipment, along with a plethora of sonar and sail sensors. The armaments appear quite decent, including a heavyweight torpedo and underwater launched AshMs. Rather than the ability merely spec'ed as many subs do, the Songs have actually and physically tested underwater YJ-8x launches, which means the ability is not something in paper, but completely operational.
Compared to the double hull of the Kilo, the single hulled Song appears somewhat behind in that feature, but then, the majority of Western submarines are single hulled and for the most part, seemed well adequate with them. However, these submarines have a good excuse for using single hulls that is not applicable to China's situation---making double hulls is more labor cost expensive due to the welding required. China may have aped a design feature from a Western sub without considering its own unique advantage---that it has in the beginning, the manpower and labor cost structure to do double hulls. As a matter of fact, China's first indigenously designed submarine, the Han, is a double hull. Another odd feature are the sensor stalks on top of the bow, which is also featured in a number of Chinese designed subs including the Yuan and the 093. It is apparently aped from similar stalks in USN subs. Although the USN subs have such stalks, the user alone does not guarantee that this is an optimal design feature, and other Russian and Western designs have gone on to eliminate such stalks, which add only to drag and noise.
Nonetheless, the Song's single hull design probably makes it faster, cheaper and easier to construct, especially using modular sections. From mid 2004 and on, the Songs were made like hotcakes. Even today, when its said that the Yuan may have replaced the Song in the production lines, this issue may be arguable. The Song works, its cheap and fast to make, and the pattern of Chinese military development reveals that China does not give a short production span on a truly cost effective and successful design.
