March 11, 2016

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
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

25 comments:

Ztev Konrad said...

There seems to be a misunderstanding about amount of reserve buoyancy required. The critical point is at depth and maybe some flooding and you need to get to the surface, not how high you want to sit at surface.

Another issue which Im interested in is Japan has deliberately understated the operational range of the Soryu for political reasons, ie they can only admit to self defence capability- which is recently noted in calling their helicopter ship a destroyer.
Realistically Japan would need to think of defending sea lanes out to the Persian Gulf for their oil supply.
A large submarine normally indicates a long range submarine, which is why Australia couldn't just buy an existing small short range Swedish sub but required a larger long range model.
What would others think of these views ?

Ztev Konrad said...

Is the AIP really that noisy ?
If we think about the process compared to a diesel engine in a sub, the Stirling type engine doesnt 'explode'a fuel-air mixture like a diesel does to create power but the fuel just burns to create the power. Plus there is no opening and closing exhaust valves.

Peter Coates said...

Hi Ztev

Wish I had your certainty. Buoyancy is unfortunately more complex - especially for double hulled or semi-double-hulled (like the Soryu) submarines. Grateful if you can furnish links or some evidence to support your insights.

This is noting Submarine Matters attempts to be an accumulation of evidence based website.

Thankyou for the invitation "What would others think of these views?"

Cheers

Pete

Anonymous said...

Hi Pete

In the home page of JMSDF [1], the standard displacement of SS ”SORYU” Class is specified as 2950t. If the standard displacement is false, JMSDF is against the law [2]. No one can steal 800tonnes of material secretly for years.

Power of 12V/25/25 S is officially reported to be 2700PS (1986kW) by JMSDF. It modified to 12V/25/25 SB [4]. Hedemora HV V18b/15Ub (210B) 1400kW/1400rpm [3]. So, we cannot conclude that diesel generation power of Soryu [3972kW =2 x 1986kW for two 12V/25/25 S] is less than that of Collins [4200kW=3 x 1400kW].

Moving parts of diesel generators are adequately maintained including exchange. The Board of Audit checks maintenance record [5].

[1]http://www.mod.go.jp/msdf/formal/gallery/ships/ss/soryuu/501.html
[2]Japanese Law, Chapter XVII Crimes of Counterfeiting of Documents, (Making of False Official Documents)
Article 156 A public officer who, in connection with his/her official duty, makes a false official document or drawing, or alters an official document or drawing, for the purpose of uttering, shall be dealt with in the same manner as prescribed for in the preceding two Articles, depending on whether or not the document bears a seal or signature.
[3]MULTI-ENGINE SUBMARINE POWER SUPPLIES: THE OPERATING CASE byJohn Buckingham and Jacob Mann, Page3.
[4,5] omitted because, too, long.

Regards
S

Peter Coates said...

Hi S

Thanks for your answers and the evidence you provide for each.

It will be up to Anonymous to argue the 3,700 or more tonne surfaced displacement subject and any implication of diesel engine power (many more variables than sheer horsepower).

An issue of wider interest may be the shorter operational life of Japanese submarines. Is is correct to say that Japan is working to lengthern the operational life through:

1. a life extention program for the Oyashios?
2. an aim to increase life to 22 years so Japan can lift deployment numbers to 22?
3. an inspection program to detect any metal fatigue issues? and
4. taking into account of the time submarines are out of the water being overhauled or not on operations?

5. Overall have MHI/KHI worked with a shorter operational life (16-18 years) for production schedule reasons which is continuous build one submarine (between them) per year?

Regards

Pete

Wispywood2344 said...

Hi Pete.


Obsolete "General rules of electric propulsion system for submarine" indicates that Harushio class submarines are equipped with 2 "SG-6" generators, and its rated output is 1850kW@1200rpm [1].
Both Harushios and Soryus use "12V25/25S" series diesel engines, so their total generator output is probably 3700kW(1850 x 2).
In my opinion, 2 diesel generators inside Soryu are enough powerful to simultaneously perform high rate LAB charging (charging current is up to 0.23C) and high speed advance (ca.11kt [2]) while snorting.
The new diesel engine probably be equipped with higher pressure cylinder (BMEP at rated power would reach to 2MPa : 48% higher than 12V25/25S).
If the cylinders dimensions and rated revolution speed are the same as 12V25/25S, the total generator output of 29SS would excess 5500kW.


Soryus are generally known that their displacement is 2950tonne, and this is the official "standard" displacement, not "surfaced" displacement [3].
It is not clear whether JMSDF-defined "standard displacement" is the same meaning of "surfaced displacement" used in this article.


Oyashio class and Soryu class can be loaded with diesel oil at least 200kL and 150kL respectively.

[1]General rules of electric propulsion system for submarine (obsolete version)
http://www.mod.go.jp/trdi/data/pdf/F/F8004C.PDF#page=39
[2]My blog article : Estimation for Soryu class submarine : relation between motor revolution speed , motor shaft output and submerged ship speed
http://blog.livedoor.jp/wispywood2344/archives/55480697.html
[3]Official specification of Soryu class submarine
http://www.mod.go.jp/msdf/formal/gallery/ships/ss/soryuu/501.html
[4]Bid announcement : refueling 200kL diesel oil to "Isoshio"
http://www.mod.go.jp/msdf/bukei/k1/nyuusatsu/20-1-1192-2105-5006.pdf
[5]Bid announcement : refueling 150kL diesel oil to "Soryu"
http://www.mod.go.jp/msdf/bukei/k1/nyuusatsu/20-1-1192-2105-5008.pdf

Regards
Wispywood2344

Anonymous said...

Hi Pete

Question: a life extention program for the Oyashios?
Answer: Yes.
Unless JMSDF has the program, Ministry of Finance would never admit the budget for the life extension.

Question: an aim to increase life to 22 years so Japan can lift deployment numbers to 22?
Answer: Yes.

Question: an inspection program to detect any metal fatigue issues?
Answer: Yes
Regular inspection is carried out. Japanese submarine has enough strength and durability for much longer operation than 18 years, also, periodic inspection was carried out. If metal fatigues generate in 30 years-use, we cannot use such submarine even for one year. Form detailed analysis of various data, I conclude the life extension of Oyashio-class is mainly carried out by exchange of LABs.

Question: taking into account of the time submarines are out of the water being overhauled or not on operations?
Answer: I do not know.
But, if the life extension is exchange of LABs, construction or exchange is huge task.

Question: Overall have MHI/KHI worked with a shorter operational life (16-18 years) for production schedule reasons which is continuous build one submarine (between them) per year?
Answer: No
Shorter operation life results from the desire of JMSDF for the latest weapon and not from schedule of MHI/KHI, I believe.

Regards
S

MHalblaub said...

So the Kawasaki 12V is an orphan engine because MAN builds just engines up to 1,300 kW.

The MTU range for the 4000 series is between 750 kW and 4,200 kW.

A submarine diesel operates different to avoid excessive vibrations and suffers about 20 % power.

What about EPA Marine Tier 3?


Type 212 runs on a single MTU 396 with just 1,050 kW.

The new MTU 4000 SE only offers up to 1,300 kW.

What is the official MTBF for the Kawasaki engines? Maintanence schedule? Availability of spare parts? Google for 4000 series spare parts and where you can get them!

Anonymous said...

My view is the conclusions are hasty without sufficient scientific or engineering proofs. The side profile measurements could equally be wrong.
I like to see a detailed treatise on how one can start from a non isometric cut away drawing and end up with a side profile. There is a science behind doing this but it is also an art. Plenty of experts have come up with the wrong answers when one estimate dimensions starting from various drawings or photos.
KQN

Anonymous said...

How can anyone looking at the KHI drawings, and they are not engineering drawings, and be able to say that the decks are rigidly welded to the hull. Please show proofs behind such statement.
KQN

Ztev Konrad said...

As an aside to the japanese system of 'short life', they have a similar arrangement for their cars, at about the 7-8 year point and very rigourous test (shaken) and examination is undergone which requires expensive replacement of many parts or for most owners they are sold- this is a prime source of cars for the used car export trade, the cars being very cheap but still very usable. ( I have one, a 2003 Honda Accord wagon). The upside for Japan is that there is good demand from home market and breakdowns are reduced for their traffic clogged cities.
In a way subs are ideal for avoiding an expensive 'half life refit' and modernisation at the 18 year mark because of the enclosed hull.

Regarding the oversized bouyancy tanks, I think a good reference would be any good review of the loss of the USS Thresher. There were a sequence of events that were presumed but one of the causes was reasonably thought to be unable to get enough buoyancy at the great depth to rise to surface. Also for operation near surface, separate trim tanks control buoyancy due to the range of weight conditions of the boat and the different salinity of the ocean or enclosed seas ( eg Baltic) These are discussed in standard submarine references.

Anonymous said...

Hi Pete

I do not whether 12V/25/25 SB is an orphan or not, but, more powerful than MAN. JMSDF explained that one of reasons of 12V/25/25 S was powerless of MAN diesel.

12V/25/25SB has developed nearly 30 years ago and new diesel is already developed. Comparison of 12V/25/25SB and latest MTU is not appropriate.

EPA Marine Tier3 and coming Tier4 are adopted for commercial marine diesel engines. Diesel engines for submarine are excluded. As number of 12V/25/25 SB is only ca. 40 and used for battery charging in a limited time, I do not think it has significant effect on atmosphere at all.

At snorkel submerging, various factors including engine capacity and rotation number as well as engine mounting and muffler should be considered. But, these are top secrets. Capacity of 12V/25/25 SB (147L) is larger than that of 16V MTU (ca. 70L?).

MTBF is aiming reduction of the design effort, is for manufacturer and not for customer. Disclosure of MTBF by MTU may be very important for Chine as promising manufacturer of evolved submarine diesel generator. Massive export of advanced weapon technology to China by Germany is much more serious than tiny secret of KHI.

Maintenance schedule is not disclosed. Spare parts are availed from reliable subcontractor.

Regards
S

Anonymous said...

Hi Pete

Big mistake of comment (11/3/16 11:12 PM)

Before correction
But, if the life extension is exchange of LABs, construction or exchange is huge task.
After correction
But, if the life extension is exchange of LABs, setting construction and/or exchange of LABs is not huge task.

Regards
S

Peter Coates said...

Hi ?????

Where someone emailing on 13 March 2016 to Submarine Matters standard comment platforms has somee Interesting For Public information but says:

"Just for your information."

What can I do with this information?

Can I publish it or not?

Regards

Pete

Anonymous said...

Hi Pete

I got hull dimensions of Soryus using my previous work.

http://livedoor.4.blogimg.jp/wispywood2344/imgs/b/8/b8308cab.gif (GIF animation of drawing process)

http://livedoor.blogimg.jp/wispywood2344/imgs/d/b/db832cb1.png (Measurement result)

Wispywood2344

Anonymous said...

Hi

I am the anonymous having given the assessment to Pete.

Please find a few answers to some comments.

- Ztev Konrad:
- About volume of ballast tanks: for most submarines, the draught you get in surface is when emptying the ballast tanks, whatever the method to do so (blowing or pumping). As far as the emergency blow is concerned, it is much more subtle: the designer may not wish to have all water ballast tanks with emergency blow and besides, the instant emergency lightening you get depends on the size of you bubble and the flow/size of ballast tanks. As such, my calculations are based on the assumption that all ballast tanks are empty for surface conditions. Most importantly, due to the shape of the partial double hull, there is simply not enough volume to fit in 4,200-2,950 tonnes of water.
- Loss of Uss Thresher: you should also mention the possibility of humid air in the HP air bottles having created ice blocking the pipes when blowing and blocking the air to go to the ballast tanks.

- KQN:
- about side profile measurements. I have been making measurements thanks to pictures and videos. Some lengths are easy to measure thanks to the casing interface with the pressure hull. Happy to have your own analysis.
- About welded platforms: have a read at the article from the technical review and prove me wrong. You can clearly see that the decks are mounted before the "modules" are slid in.

- Wispywood2344: in terms of DG set power, I would be happy to get more details on how you can get so much power whilst guaranting 30+ years of life expectancy. I think it is a new realm and very different from the usual 15 years of life -expectancy of the japanese boats. Besides, I have made some calculations with the power of the Kawasaki 12V/25/25SB, assuming 2x1,850=3,700 kW. the indiscretion ratio would be 100% at 10 knots which means, you snort all the time! So I agree much more power is needed, I am just curious onhow it can be achieved.

- S: you compare two 12V/25/25 S [3972kW =2 x 1986kW ] and Hedemora HV V18b/15Ub (210B) of Collins [4200kW=3 x 1400kW] but the first ones have a de-rating for 16-18 years of life expectancy whereas the others are for 30 years+, and that is a massive difference that could cut the Kawasaki power by 20% easily. So, sorry but not even close to Collins which are smaller so with less drag when snorting so more power for the batteries.

kind regards

Peter Coates said...

Thanks Wispywood2344 [13/3/16 11:25 PM]

The Soryu .gif animation is particularly interesting.

It gives an idea how computer aided designers work.

Regards

Pete

Anonymous said...

Hi Pete

On “NO ELASTIC MOUNTS ON SORYU”

MOD established the standard for anti-vibration rubber used in naval sea system in 1970 and has maintained after that. This standard is based on two US Military Standards [1, 2] and is partially newly developed. The aim of this standard is reduction of underwater radiation noise. I do not think that MOD excludes Soryu from application of this standard.

[1]MIL-M-17191D(SHIPS)(MOUNT, RESILENT, PORTSMOUTH BONDED SPOOL TYPE
[2]MIL-M-17508E(SHIPS)(MOUNTS, RESILIENT: TYPES 6E100, 6E150, 7E450, 6E900, 6E2000, 5E3500, 6E100BB, 6E150BB, 7E450BB, AND 6E900BB)

Regards
S

Ztev Konrad said...

This may be of interest , its published by RINA, and covers a discussion by MTU about their diesel developments, specifically those used by submarines.

MTU and MAN normally license their technology to other builders
http://www.rina.org.uk/Series_4000_to_form_basis_of_new_submarine_diesel.html
One completely new feature of the 4000 submarine engine is the ability to operate in different modes. The standard operational mode is ‘acoustically optimised’ mode. In this mode of operation, the engine has the lowest air- and structure-borne noise emissions with a specific fuel consumption improvement of at least 5g/kWh. For long operational periods in transit to a theatre of operations, the engine can be switched to a ‘fuel consumption optimised mode’ with slightly increased acoustic signature. “This will allow reduced specific fuel consumption of at least 10g/kWh,” von Drathen explained. Finally, for surface operation, an ‘emission optimised’ mode is selectable. The emission optimised mode operates under IMO 2 compliant conditions without increasing the specific fuel consumption.

high shock and acoustic requirements demand special attention to the way that the generating set is mounted in the submarine and the new engine foot for the Series 4000 includes what von Drathen described as “an integrated movement limiter.” It is compact and easy to install and helps to reduce structure-borne noise associated with the engine.

It seems that the shock resistance isnt just a matter of an isolated raft but moving that further up to the noise making equipment itself.

Peter Coates said...

Hi Ztev [12/4/16 12:12 PM]

Thanks I'll put many bits into the Recalculations text tomorrow.

Regards

Pete

Peter Coates said...

Hi S and Ztev

Thanks for you help. I have now corrected the "Recalculations" article indicating Japanese subs extensively use elastic/rubber mounts for sound dampening.

Regards

Pete

Peter Coates said...

Hi Ztev [12/4/16 12:12 PM]

Thanks for spotting http://www.rina.org.uk/Series_4000_to_form_basis_of_new_submarine_diesel.html .

I'll use that to write an article on the MTU 4000 for submarines next week

I'll also include http://www.prnewswire.com/news-releases/rolls-royce-and-china-yuchai-to-jointly-produce-mtu-engines-300222849.html on MTU 4000s to be made/further developed in China, maybe for Yuan subs?

Regards

Pete

Archimedes said...

Hi Peter

About elastic mounts: let's be clinical.

The important statement is that Japanese submarines have equipment each on elastic mounts BUT they DO NOT have large platforms (weighing a few tonnes with these pumps, motors etc) themselves elastically mounted on the hull, such as on the image below.

http://urrg.eng.usm.my/images/bulletin/vol2/vol2_oct15.jpg

So basically, the Japanese use welded decks to the hull with each SINGLE equipment elastically mounted on them instead of LARGE platforms elastically mounted to the hull, thus creating a DOUBLE stage of vibration insulation between noisy equipment and the hull.

Keypoint: size of the platform has a HUGE impact on noise mitigation. Double stage mounting without large platform is nowhere as efficient.

Once again, with the Japanese approach, we are looking for something like 20 dBs of radiated noise (acoustic signature) degradation at 1 kHz, compared to what Collins subs have today.

Finally, let's not even try to imagine for a moment that Japanese equipment are less noisy than the Australian components by that number of dBs or that the acoustic tiles on the submarine hull can make up for that shortcoming.

kind regards

Archi

Peter Coates said...

Hi Archi

Its difficult to verify the type and extent of elastic mounts on Soryus. Such information may be mainly classified.

Many of the elastic structures may not even be included in drawings/diagrams that are publicly available.

Maybe more will be revealed with the visit of the Soryu sub to Sydney April 15-23 2016.

Regards

Pete

Anonymous said...

Hi Pete

The floating deck is adopted for Stirling AIP section [1], and four Stirling generators [2] (3t in weight) are elastically mounted [3] on the floating deck. Currently, the floating deck [4] is partially adopted, but it will be fully adopted for next Japanese submarine. Varieties of anti-vibration rubber are adopted [5] for warship, and some of them are adopted for submarine.

[1]http://www.mod.go.jp/atla/research/dts2012/R2-2p.pdf, page 7/17. This figure shows improvement of quietness in Japanese submarine, and upper right of the figure reveals that AIP区画浮甲板(floating deck for AIP section) is adopted for Soryu-class.

[2]http://www.docfoc.com/stirling-engines-Go3wW, page 2, paragraph 2, “the dry weight of the engine is 750 kg”
The said engine means Kockums V4-275R Stirling engine whose upgrade version is used for Soryu-class.

[3]http://www.mod.go.jp/atla/nds/F/F8018D.pdf, page30. NDS F8004 2 ”General rule on AC electric motor” 5.2.11.2e)

[4]https://www.khi.co.jp/rd/tech/154/nj154tr08.html, KHI Technical report, vol.154, “ Development of the shock isolators for warship”. The shock isolators for the floating deck were illustrated in Fig.3. Actual shock isolators will be modified and different shaped, and vertically and horizontally applied for the floating deck.

[5] http://www.mod.go.jp/atla/nds/F/F7501D.pdf, NDS F7501D ”Anti-vibration rubber for equipment of warship”

Regards
S