Extra Issues: Singapore's 218SG (Invincible-class) Submarines

The 218SGs largest cutaway diagram (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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Since SubMatts’ most recent article on Singapore’s Type 218SG Invincible-class submarine Anonymous and retortPouch have provided very interesting extra comments. These are summarised below:

Section 1.

Looking at Cutaway above provided by retortPouch, Anonymous has made the following comments on Singapore’s Type 218SG Invincible-class submarine: (hereinafter called just 218). The 218 will not be purely single hulled or double hulled but instead “mixed hulled”. This is with an inner pressure hull steel shell estimated at HY100 throughout but also outer hull sections surrounded by FRP (Fibre Reinforced Plastic). Between the hulls are fuel and seawater buoyancy tanks and such fittings as sonars, other sensors and ejectors as well as tanks which can more safely store flammable/explosive Hydrogen packaged (more safely) in Metal Hydride (MH) form.

If HY100 pressure hull steel is used (as in Type 214s) this is likely magnetic and allows the submarine to dive to ocean depths with water pressure equivalent to 100,000 pounds per square inch (psi) or 690MPa. This steel’s thermal conductivity is estimated to be 34 W/mK) making it a “conductor”.

It is possible that the 218 will use HY80 (560MPa) pressure hull steel (as used in Type 212As) which has the advantage of being non-magnetic, hence less detectable. However if the 218 (shaped like a 214 has HY80 steel (like a 212) then the 218's whole hull structure (supporting frameworks and all) will need to have been revised from scratch, rather than closely copying an existing structure.

Non-pressure “outer parts” of the 218 hull use FRP also called “composite” materials which have an estimated thermal conductivity of (0.5-0.1W/mK) making them semi thermal insulators.

The following is very complex. Heat from reactions in the 218's Proton-exchange membrane fuel cells (PEMFC) AIP is used for heating of liquid inside fuel cylinders. An FRP plate might act as a rupture vessel to prevent  leakage of hydrogen from MH cylinders. FRP plates are fixed by bolts (white spots) not because of non-magnetism, but because of thermal/heat insulation of fuel cylinders in the space between pressure hull and FRP plates. A MH cylinders are encased within a cylinder surrounded by liquid (maybe diesel fuel). Cool liquid is carried into a fuel cylinder at hydrogen loading and cools hydrogen absorbing metal inside the MH cylinders. Hot liquid is carried in a fuel cylinder at hydrogen generation and heats MH inside of a MH cylinder to generate hydrogen.

Section 2. On other issues - from retortPouch:

Excellent details of Singapore broader submarine issues here https://www.channelnewsasia.com/news/commentary/singapore-poison-shrimp-strategy-new-submarines-type-218sg-11260946 

Correction: It turns out Singapore's 2 Archer-class submarines will be retired after 2024, as indicated by 2019 plans.

Furthermore:

a) as of 2019, the 218s will not be armed with land attack missiles, however

b) it is likely, by the phrasing of the author, that it will be able to operate UUVs. Other relevant items come in the last few paragraphs, like underwater submarine safety/codes of conduct.

1) https://pbs.twimg.com/media/EXwDtQ_U0AADx3n?format=jpg&name=small

218 going through sea trials, shared on Twitter by David Boey, original article here https://www.shz.de/regionales/kiel/neues-u-boot-invincible-auf-der-kieler-foerde-zu-sehen-id28288867.html ; photos courtesy Rolf Dunkel.

2) https://twitter.com/tpenghui/status/1131731710805024768?s=20

Tpenghui/Faithkeeper confirms, via TKMS marketing that the 218 will have a new design of ultraquiet screw/propeller, and the large ring, as suspected, was to optimise flow, and make it cleaner for the screw. [see second photograph of the IMDEX Asia 2015 model]

3) https://twitter.com/tpenghui/status/1129189192540442624?s=20

Tpenghui/Faithkeeper confirms that the pressure hull will be steel, however the upper angled "tent", and the massive keel structures will be made of non-steel, non-magnetic materials to reduce the magnetic signature of the sub. [This can tie in with discussion of combination of pressure hull steel and FRG/composites in Section 1. above].

4) The 218s will come with vertical locks (possibly not vertical multi-purpose locks (VMPLs) but probably not the sail lock solution) to launch divers and UUVs.

https://pbs.twimg.com/media/DABDlQFUAAA8lX_?format=jpg&name=medium

This is an old model photo from the 2017 TKMS booth at IMDEX Asia, taken by Tim Fish/@sweeneygov, look at the cutouts on the top surface of the "tent". [Also see IMDEX Asia 2015 models].

Anonymous and retortPouch