Potential Soryu Problems - Recalculations

CORRECTION - JAPANESE SUBMARINES EXTENSIVELY USE ELASTIC/RUBBER  MOUNTS FOR SOUND DAMPENING

There have been anonymous statements around the Web that claim Japanese submarines have no elastic mounts. Such statements are incorrect.

Retired Vice Admiral Masao Kobayashi, former Commander Japanese Submarine Service,  reported January 18, 2015, concerning the extensive sound reduction measures on Japanese submarines:

Pointing “to the ceiling lights in the quiet interview room and said: “Take those fluorescent lights, for example. Any fluorescent light generates sound.”

Other than our voices, there were no other sounds in the room.

“Fluorescent lights generate extremely small vibrations. We take anti-vibration measures for every single light in a submarine,” he said.

Japan’s engineers have painstakingly worked to minimize the vibrations given off by the multitude of components in submarines to prevent even those undetectable by the human ear from being picked up by the super-sensitive sonars of enemy subs and sonobuoys from anti-submarine aircraft, Kobayashi said.

Noisy components include fans, pumps, motors and fluorescent lights. Some are carefully muted with vibration-damping rubber, he said.

“The quiet submarines we have today are the result of numerous long, patient efforts,” Kobayashi said.

In December 2015 Takehiko Hirama, Commander of the Soryu submarine SS Kokuryu reported:

"We can go into enemy territory without being found out because we emit very little sound."

Every piece of the submarine is designed to minimise sound signatures or vibrations...All the electronics are also covered in rubber to mute any noise, and even the light bulbs have had their sound signatures extracted.”

Japanese Ministry of Defence (MoD) standards since 1970 have required Japanese naval vessels (ships and submarines) to have anti-vibration rubber. The aim of these standards is reduction of underwater radiation noise. These standards are based on two US Military Standards:

-  MIL-M-17191D(SHIPS)(MOUNT, RESILENT, PORTSMOUTH BONDED SPOOL TYPE, and

-  MIL-M-17508E(SHIPS)(MOUNTS, RESILIENT: TYPES 6E100, 6E150, 7E450, 6E900, 6E2000,

    5E3500, 6E100BB, 6E150BB, 7E450BB, AND 6E900BB)

Another Japanese MoD standard for anti-vibration rubber is NDS (Standards for Mod) F 7501D “Anti-vibration rubber of equipment for warship”. On page 18, 1. “This standard aims reduction of underwater radiation noise in warship” and page18, 2.(1)(c) “Conventionally, scope was limited to hull and main and auxiliary propulsion,

In terms of auxiliary propulsion the standard NDS F8004 2 covers anti-vibration rubber in relation to the Stirling AIP engine. 

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Click on image to enlarge.
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To calculate the Soryu's real size estimates were made using standard published information. On the basis of the cut-aways (top) and other published diagrams a side drawing, with meter measurements,  (immediately above) was created. This is all part of reverse-engineering the Soryu's principal particulars.

The conclusion (in summary) was:

-  difference between calculations and standard published information is 800 to 1,100 tonnes and

-  the Soryu is bigger by 25% to 33% in reality. 

A heavier submarine requires more engine power and fuel to achieve speed-range requirements. The disparity in surface displacement (2,900 tonne published, but 3,700 tonnes estimated) would particularly impact the Soryu's surfaced, speed-range. 

SPECIFICATION  (with wiki published figures if available)	CALCULATION
Pressure hull calculated volume:	3,300 m3
Pressure hull displacement:	3,300 x 1.025 (average seawater density) = 3,382 tonnes
Estimated ballast tanks:	500 tonnes
Estimated external fuel tank:	150m3 – 127 tonnes. Not sure much room left for more inside, even alongside batteries (compensating tanks and others need room too!)
Estimated submerged displacement:   (4,200 tonnes published in wiki)	>4,200 tonnes (between 4,200 to 4,500 tonnes)
Estimated surface displacement:  (2,900 tonnes published in wiki)	>3,700 tonnes (= 4,200 tonnes – 500 tonnes): (between 3,700 tonnes to 4,000 tonnes)
Estimated accuracy of calculations:	300 tonnes (7 to 8%)
Difference between calculations and standard published information:	800 to 1,100 tonnes!
	Soryu is bigger by 25% to 33% in reality.

ANONYMOUS COMMENT

"So that tells you something about Soryu's real size...

The reserve of buoyancy is indeed 13-15% on that submarine (500/3700). Sorry, not possible to add more ballast tanks, because your submarine would be too high on the water. And the pictures tell us that Soryu's draught is around 7.6-7.8 m. So I made the calcs on my software tool, they check out. !

And yes, these two diesel engines (Kawasaki 12Ｖ 25/25 SB-type)'s power is unknown. Anyway, it will be less power in total than on Collins (with Collins 3 × Garden Island-Hedemora HV V18b/15Ub (VB210) 18-cylinder diesel motors), even with a favourable de-rating due to shorter life-expectancy.

Shorter life expectancy raises another interesting point: the Japanese  keep the same 2 Kawasaki diesel-generators sets on Australian Soryu but claim to extend Future Submarine life to 35 years; so either you de-rate their power by, say 50% and there is little left, or you ditch the engines every 15 years  (current life span of Japanese boats)? by cutting the hull (can their steel accommodate that?). At the end of the day, the winner is: higher indiscretion ratio than Collins! 

And fuel storage: largely inferior to what is needed. you would need to add 50% for the 3rd diesel and double the lot to have Collins legs. Issue: Soryu's design would become infeasible and diverge due to added length and drag etc...

SIMILAR DOUBTS

Geoff Slocombe, writing in the ASPI Strategist, March 11, 2016 also has doubts http://www.aspistrategist.org.au/sea-1000-is-there-a-strategic-necessity-to-choose-the-japanese-submarine/ :

“Modern European submarine construction uses a single pressure hull, while the Soryu class uses a combination of double pressure hulls for the forward and aft compartments, but with a different steel alloy from single pressure hulls for the intermediate four compartments. Does this create differential expansion/cracking and corrosion problems at the dissimilar metal junction and is this the reason why Soryu has a 20 year life, not the 30 required by Australia?

While double pressure hulls increase a submarine’s reserve of buoyancy, they also increase cost and complexity of manufacture, probably give a shorter planned sea life, and increase the wetted area of the submarine requiring more energy to propel the vessel underwater.

A 4,200 tonnes Soryu has a crewing capacity around the same as Israeli Navy’s 2,400 tonnes Dolphin 2 Class submarines. The physical layout inside the current Soryu won’t meet ergonomic standards for future RAN submariners, affecting their alertness, health and welfare during a long range/endurance mission. Arguably the current Japanese internal design is inefficient and a poor starting point for an evolved Soryu detailed design.”

PETE'S COMMENT

The Anonymous calculations and observations tend to reinforce comments I made in a Submarine Matters article of February 12, 2015 where I wrote:

"One additional issue is that the Japanese Navy has been running its submarines with the assumption the service life is 15-20 years - while Australia assumes submarines should be in service for at least 30 yours. This may or may not be a problem. After 15-20 years moving parts may or may not start to wear out. This may be most significant in the submarine's diesel engines and the very large electrical motor. Changing engines-motors is very heavy maintenance involving cutting into the submarine hull. This might only be possible in Japan for the Soryu? Maintenance realities may or may not be a problem.

Anonymous and Pete