Comparison of Soryu Modes of Electrical Propulsion Table

On March 16-17, 2017 Anonymous made some comments that I have semi-translated and turned into a table.

The rows below show:

-  current Soryu Mark 1s (Stirling AIP & LABs)

-  future Soryu Mark 2s (LIBs only) and

As well as two hypothetical Soryu models:

-  Soryu X (Fuel Cell (FC) AIP & LABs), and

-  Soryu Y (Stirling AIP & LIBs))

Soryu modes of electrical propulsion are compared according to criteria in the first column.

70 day mission = 20days transit + 50days surveillance	Soryu Mark 1s (AIP & LABs)	Soryu Mark 2s (LIBs only)	Soryu X (FC-AIP & LABs)	Soryu Y (AIP & LIBs)
Numbers of batteries 1] [2]	480 LABs	576 or 672 LIBs	480 LABs	480 LIBs
Submarine size (length)	length 84m	78-83m	same	same
Crew shifts	3 shift crew routine	Same	Same	Same
max fully submerged period in theory period - (actual) in days [3]	LABs+AIP 16-17 days (15 days)	LIBs 7-8.5 days (6-7.5 days)	LIBs +FCAIP 32 (33)	LIBs+AIP 20 (19)days on
Percentage LOX unused	most LOX kept in reserve	N/A	30% of LOX kept in reserve	most of LOX kept in reserve
frequency of snorting/recharge [7] theory (actual)	6-12 hours LABs	Within 6 days (1-2 days)	1-2 days on FCAIP+LABs	5days (1-1.5days) LIBs
LIB types used and [4]	none	Lithium Nickel Aluminium oxide (NCA)	none	Lithium Nickel Aluminium oxide (NCA)
The future? [6]	No Soryu Mk. 1 new builds after 2014 [5]	Evolved LIBs or Li-Sulphur Batteries (LSBs)	none	none

[1] Although the combination of AIP + LIBs had some advantages the JMSDF preferred increasing the number of LIBs (576 or 672 LIBs on Soryu Mark 2s) compared to only 480 LABs on current Soryu Mark 1s). Major reasons for the change in propulsion were the low utilisation ratio of AIP and need for high speed performance.

[2]  The reasons why the Japanese Navy (JMSDF) gave up AIP for the Soryu Mark 2s (LIBs only)) are not clear. Possible reasons are:
i)   poor endurance of Soryu Mark 1s due to weight and bulk of the 2 x LOX tanks

ii)   low frequency of AIP use

iii)  complex operation of diesel engines, AIP and LABs

iv)  demand for high speed performance, which low submerged speed Stirling AIP cannot efficiently contribute to

v)   LIBs last more years than LABs ie. LIBs can function for more cycles. Lithium Titanate (LTO) shows an extremely long life time, and total life time cost may be the same or less than for LABs.

vi) Though there is an another attractive option, ie. AIP+LIBs, instead of increased LIBs, AIL+LIBs was not selected. This suggests that the contribution of increased LIBs (96 or 192 LIBs) was greater than that of AIP. Presumably based on operational experience and submarine tactics, the JMSDF prioritize high speed performance (such as longer period at max silent submerge speed) over long submerge period at low speed provided by AIP.

[3]  The fully submerged period of a Soryu Mark 1 (LABs + AIP) is said to be as short as 2 weeks. So AIP is possibly not used for ordinary missions. Possible uses of AIP are as follows:

i) emergency such as combat

ii) modulation of snorting-recharge timing to avoid undesirable timing which may be caused by Low energy density of LABs.

The maximum discharge of LABs and LIBs are assumed as 30% and 90%, respectively. Further discharge leads to irreversible damage to batteries.

[4]  12 years ago the JMSDF demonstrated that the energy density of prototype LIBs was twice that of LABs. The LIBs for Soryu Mark 2s are much better than the LIBs prototype.

[5]  See the SORYU-Oyashio Build, Launched and Commissioned Table of March 22, 2017 (below).

[6]  A future sub with AIP and LIBs may have an excellent indiscretion ratio. But, improved LIBs or Lithium-Sulphur Batteries (LSBs) are a more feasible option for the JMSDF.

[7]  For LABs, more frequent snorting-recharge avoids the submarine running out of electrical power at a bad place and/or time. For LIBs, frequency of snorting-recharge drastically decreases. A lower longer frequency for LIBs of snorting-recharge every 6 days is possible, but, after 6 days snorting-recharge takes longer.

Anonymous and Pete