In comments below http://gentleseas.blogspot.com.au/2015/08/australias-naval-shipbuilding-blueprint.html“S” has provided very interesting views on Japanese-Australia submarine issues. This is concerning the Soryu and Collins.
The actual submarine designs that are being proposed for SEA 1000 will be significantly different from current subs - but discussion has more substance when on the basis of current subs. The Japanese proposal, which will likely win the SEA 1000 CEP, is likely to be an evolution of the Soryu.
One concern is that the operational period of postwar Japanese submarines, including the Soryu is significantly shorter than the 30 year average for submarines designed in Europe or the US.
I have clarified the English in S’s responses and hope this clarification is faithful to his intended meaning. On August 5, 2015 S indicated:
That he thought that having set views on average years of operation of a submarine without considering the rate of operation is “meaningless.”
“Submarine hull will experience physical, chemical and chemical-physical degradations such as fatigue, corrosion and stress-corrosion cracking. Also, mechanical parts such as diesel engines, batteries systems and AIP systems will deteriorate. These degradations will come up only under actual operational conditions. For example, if there is no repeated surfacing-submerging, the fatigue of the hull caused by repeated application and release of external stress is not experienced.
It is said that the rate of operation of the Soryu submarine is 80%. As operational period of Soryu is 24 years, actual operation period becomes ca. 19 years (= 24 years x 0.8). In the case of the Collins submarine, the rate of operation is obviously lower than that of the Soryu. For the Collins’ 60% operational rate over a 30 year operational period, the actual operational period becomes 18 years (= 30 years x 0.6) which is nearly same as that of Soryu.
[Best to consider the] increase in numbers of submarines [and] also improvements in the rate of operation.”
On August 6 I asked S five questions – and below each I have provided S’s responses, also provided on August 6. I have added follow-up questions in bolded italics.
1. Why is the "operational period of Soryu 24 years"?
S answered “Submarine operational periods used to be as short as 18 years, and JMSDF [Japanese Navy] was criticized. Also National Defense Program Outline FY 2011 decided to increase number of submarine to 24 including 2 training submarines.”
Was the previous requirement for 16 or 18 submarines?
2. Why not 30 years like Germany, France and almost all other submarine builders?
S answered “Submarine building span in Japan is in line with Long-term or Mid-term Defense Buildup Plan and technology innovation.”
So are the following factors important in the number of years of operational life for a Japanese submarine?:
2.1 Is there a need for continuous build by KHI/MHI?
(The pattern of launching and commissioning one submarine per year appears to be very important. Continuous build would keep the workers (eg. welders) busy and would make budgeting more certain for the JMD and KHI-MHI.)
2.2 I have a theory that the reason the Yield Strength of the pressure hull steel is very high (at NS110 = HY156 see Table) is due to deep diving needs. So does deep diving put greater stress on the pressure hull – leading to more rapid degradation – resulting in shorter operational life?
3. What happens if Australia needs to lift availability of its Japanese built submarine to 80% in time of strategic need?
S answered “I think that Australia may reduce defense cost as a result of reduction in number of submarines.”
4. What happens if Australia wants to cut the NS110 pressure hull and reweld it to do major maintenance work (including large parts replacement on the propulsion system) or major emergency repairs?
S answered along the lines: Hull cutting significantly weakens the pressure hull thus limiting diving depth. [JDS Asashio (see SS-589 converted to testbed submarine TSS-3601 preceded Oyashio Class has an NS110 and NS80 pressure hull like Soryu Class) required hull-cutting for the experimental fitting of the large Stirling AIP system. After this hull-cutting the submerged depth of Asashio was limited.]
5. Can this pressure hull cutting-rewelding work be done in Australia?
“Aside” [this depends?] “whether JMSDF agrees NS110 technology transfer or not, advise from Japan is required, because Japan has an experience of hull-cutting of [the NS110 and NS80 pressure hull for the] “Asashio”.
Thankyou S.
Please connect with previous Submarine Matters articles, including:
Technical Problems: Fuel Cell AIP and Hull Cutting of June 25, 2015, and
Pete