Singapore’s Type 218SG (Invincible-class) submarine ISSUES

On June 15, 2020 new commenter “retortPouch” made some comments on Singapore’s current 2 Archer-class submarines, Type 214s and, in much greater detail Singapore’s Type 218SG Invincible-class submarines. retortPouch numbered the sections 1) to 13). There will eventually be 4 x 218SGs. Pete has added many links (other than the 3 Key CUTAWAY links, from retortPouch):

“1) It's almost certain that the Archers will be kept in service for a while longer maintaining a six boat fleet [ie. 2 Challenger-class, the 2 Archers and 2 x 218SGs (due for delivery 2021-22)] . The Archers are said to have had significant upgrades c.a. 2010 for which one particular Dr. Tan Beng Hock won the Defense Technology Prize in 2013.

2) It's actually very informative to make a comparison between the three HDW/TKMS Type 214 derivatives: the "basic" 214, the Turkish 214TN Reis-class and the 218SG.

Key CUTAWAY links:

a) 218SG largest cutaway (above – click here for a greatly enlarged image) (Cutaway courtesy https://www.naval.com.br/blog/2019/02/18/invincible-primeiro-submarino-type-218sg-de-singapura-e-lancado-na-alemanha/ )

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b) Turkish Type 214TN "Reis" variant. Largest cutaway (above – click here for enlarged image) (Cutaway courtesy https://www.monch.com/mpg/news/naval-channel/4361-turksub.html )

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c) Generic Type 214 above. For Largest cutaway (click here) (Cutaway courtesy http://www.naval.com.br/blog/wp-content/uploads/2008/12/u-214-schnittbild.jpg )

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3) Comparing the cutaway diagrams, using the central console as a central point of reference for size, we see that there is about a two and a half meter extension fore of the sail, and about a similar extension aft of the sail compared to the generic 214.

4) The area with bunk beds in the 218SG is almost certainly a reconfigurable space serving alternate duty as Spec Ops hotel, or Torpedo/Payload Room, or part of each at the same time. It is however the same size (between the Galley and the start of the Torpedo launch tubes) as that on the 214TN/Reis class.

5) [AARONQFW advises that compared to the Turkish Reis 214 variant (ie. 214TN), about 1 meter of the extension aft of the sail is in the engine room, about 1 meter is an enlarged combat center, and about half a meter is an enlarged technology room.] Try scaling it identically and superimposing the images to see. Maybe the 218SG's shtick really is "engaging targets at longer range" as the Defence Ministry puts it, and remote sensing/distributed swarm tactics with UUVs to "sense targets at greater range". Perhaps it is fitted for the DM2A4 ER SeaHake torpedo? See the SeaHake arms-showed here https://www.youtube.com/watch?v=TYvt3tU2yqU .

6) The extension aft of the 218SG sail seems to be distributed throughout the engine room, and in the cutaway it appears to be used as empty space, but the cutaway seems to omit a lot of important things; it's almost like somebody turned off a few layers on a Computer Aided Design (CAD) rendering. We can only speculate (and I encourage you to speculate!) as to what might be contained in the engine room, because it's not typical of the Singaporean military to sacrifice equipment for comfort. If anything their stuff is chronically over modified.

7) The 218SG might not have a Horizontal Multi-Purpose Lock (HMPL) for Special Operations (“SEAL” diver) delivery; the airlock might be located in the base of the sail instead like the German and Italian Type 212As and the Greek Type 214s. However, no pictures are forthcoming of the 218SG sail itself. There is however, one picture of the 218SG bow during the February 18, 2019 commissioning ceremony on Alamy Stock Photos here, showing that like the classic 214s, the hydrophone and most of the larger sonar equipment is probably housed below the torpedo tubes. [Pete has used a Straits Times' image below due to copyright concerns]. 

Type 218SG Invincible-class  Bow from the Straits Times, February 18, 2019.

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8) The 218SG screw/propeller is obviously missing from the cutaway (which makes you wonder why they omitted the screw when HDW screws are very well photographed), and there are no extant pictures of the 218SG's screw. However, the cutaway shows a Propeller Boss Cap Fins (PBCF) in place of the traditional hub, and a large ring like shroud for several very thin, straight blades, probably non rotating. A very interesting device which I have not seen anywhere else. It have something to do with flow optimization, or it might have something to do with reducing cavitation. I recall some years ago on your blog a commenter said it had to do with a torpedo or towed array; as far as I can tell this is not the case since there are no torpedo tubes to the rear, and plenty of submarines with towed arrays function well without it.

9) The 218SG is quite a thin submarine with respect to draught. It's unlike the German/Italian Type 212A and Israeli Dolphin 1s and 2s, (which are more similar to each other than to the 214 derived series), and is probably not a true double decked design.

10) Depending on how long you think the Upgraded Västergötland-class [becoming Singapore’s 2 Archer-class] [and the Swedish Navy’s 2] Sodermanland-class Stirling subs can endure underwater, the 218SG has anywhere between 3 and 6 weeks' endurance (half again compared to Archer class, according to the Singapore’s Defence Ministry). My guess is that the rear of the 218SG is used to house more Liquid Oxygen LOX / Metal Hydride MH, or more batteries. If it's batteries, then it's got to be lithium ion, because lead acids are too bulky and there's no point having more of them then. By a back of the envelope calculation, you'd need 13 to 14 tonnes of LOX to go 2,880 nautical miles, or 4 knots continuously at 60 to 70 percent reactant efficiency (which is ballpark for 4 knots for the SINAVY PEM 120kW cells, at 60 to 70kW total propulsion load) for 30 days. This works out to about 11 cubic meters of LOX (and a smaller volume of MH), which is quite a bit but not so much.

[Note retortPouch later wrote: “Sorry, I forgot to account for cell voltage in the basic calculation, the quantity can be divided by 0.6 for standard fuel cells giving 22 tonnes or 19 cubic meters of LOX, however Siemens claims the SINAVY PEM 120kW models run at about 1 volt cell voltage, which makes the calculation accidentally correct.”]

The alternative is between 100 cubic meters to 300 cubic meters worth of Lithium-ion batteries (LIBs). Instead of a full LIB solution, the 218SG might employ a very large load of LOX, perhaps up to 20 cubic meters worth for recharging, and a larger than normal volume of batteries, which might be LIB. HDW/TKMS is known to have explored LIBs for the Type 216 [offered to Australia up to 2016 under the SEA 1000 competition], and as early as c. 2009, the below linked Singapore publication states specifically that HDW is researching replacing lead acid with lithium ion. In that case, the advantage would be a much larger sprint/surface reserve battery capability, mitigating the problem with the old Swedish subs.

See Introduction to Submarine Design by Singapore’s (?) Ong Li Koon, Liu Chee Kong and Toh Chee Wee at https://www.dsta.gov.sg/docs/default-source/dsta-about/introduction-to-submarine-design.pdf?sfvrsn=2

11) At the [TKMS? Kiel?] dockyard, the bottom of the [218SG?] hull seems to be much blockier than the TKMS-Israeli Dolphin or classic Type 214. I speculate that it might provide extra strength, external reactant storage, and larger sensors. At the commissioning dockyard, I could not find any photo evidence of a side payload bay.

12) The contract price for the first two 218SG subs was stated in press releases to include logistics, training and the actual construction. At US$900 million per sub, if we assume half the costs go to logistics (spares) and training, the remaining half goes to the sub, which is about half again more expensive than the classic 214s that Korea and Greece received, which went for about US$300 million. The 218SG's construction costs are in the ballpark for a Type 212A but of course this is the purest kind of speculation.

13) Funnily enough, the diagram of the 218SG linked above, which the Singaporean Ministry of Defence released, appears to be an isometric projection, whereas the 214 and 214TN(?) are both orthographic projections. It's as if they just took a screenshot in AutoCAD and released it to the publicity people. Cheap on the minor, splurge on the major, classic.

The 218SG might actually be shape up to be the smallest oceangoing capable submarine in service. Its shtick might be long submerged range, long engagement range, and long sensor range in a distributed swarm."

retortPouch