Larger diesel sections better for long range submarines. A Dutch Type 212CD?

Following the article of September 23, 2019 Anonymous has kindly provided, in late September 2019, further comments and links here and here. This is on submarine (diesel section) hull diameter matters. Pete has done some editing to put the comments into standard English and added some extra comments in [...] brackets.

The article below is most useful in calculating the probable diameters of the “double hull” (ie. pressure and light outer hulls) of the future Norwegian and German TKMS designed and built Type 212CD (Common Design) and possibly a larger Type 212CD design for the Netherlands.

The German and Norwegian Type 212CD will be designed for short to mid range missions. [But the Netherlands might in future purchase an enlarged (eg. wider diameter (aka beam)) long range (for Caribbean and Middle East missions) version of the Type 212CD. This is noting that the diameter of a double hull around the diesel section, discussed here, may be less than the largest diameter (published beam) measure. The largest diameter published as “Beam: 8.4m” for the Walrus class may be around the crew quarters and/or control room of a submarine, with a small diameter/beam around the diesel section.]

On long range (oceanic) submarine missions diesels must be capable of a relatively complex level of maintenance at sea. [The maintenance crew need space to use large tools and to slide bulky spare parts into the diesels.] This requires sufficient space in the diesel section. The space inside the double hull of the Netherlands’ Walrus submarines is extremely tight for the Walrus’ 3 diesels [1]. Therefore, this space must be improved/enlarged for the Netherlands’ “Walrus Replacement” future submarine.

Case 1: for the fuel cell air independent propulsion (FC AIP) system oxygen tanks and (hydrogen storing) metal hydride cylinders are placed, for safety, outside of pressure hulls (Type 212A style). The outer diameter of the diesel section should be at least 1m wider than the pressure hull [2-4]. This means the [diesel section] diameter of a 212CD is 7.8m ( = 6.8m + 1m). In this case, the maintainability of diesel will not be as good as case 2 (but still better than the Walrus current diesel section beam?). Still having hydrogen and pure oxygen outside the pressure hull is safer.

Case 2: oxygen tanks inside the pressure hull and metal hydride cylinders outside the pressure hull [but still within the light outer hull] (Type 214 style). For better maintainability, the space between each of the 3 diesels should be 400mm-500mm wider (ie. diesel section diameter of 7.5m-7.8m = 6.3m + 400-500mm x 3 [5] [6] ). [This is greater than that of a [2 diesel, maximum 6.3m beam] Type 214 submarine.

Considering Cases 1 and 2, a diesel section diameter of approximately 8m is reasonable (= around 15% wider). Increase of 15% in beam means an increase of 30% in displacement (2,000t for Type 214 becomes 2,600t for a wider beam) [for a Netherland’s Walrus Replacement/future submarine 212CD]. 

[Note this is not suggesting the smaller/standard Type 212CD for Norway and Germany will be 2,600 tons – more likely their 212CDs will be approximately 2,000 tons maximum/submerged].

[1] from https://naviesworldwide.com/navy-news/do-conventional-submarines-need-diesel-engines/ (above) Diesel engines in the Netherland's Walrus class submarine take up a lot of space, require staff and maintenance. [The engine maintainer in the photo looks exposed to the danger of hot engines.] (Photo courtesy Jaime Karremann / Marineschepen.nl)

[2] above is a cutaway diagram from http://gentleseas.blogspot.com/2019/02/tkms-type-212cd-submarine-propulsion.html The complexity of hull diameters along the single diesel 212A above is evident. The maximum diameter of the light outer hull (the "Beam") is known to be 6.8m and the diameter of the pressure hull may be approximately 5.5m. If a 212CD had 2 diesels its pressure and outer hull measures would need to be approximately 1m greater.

[3] https://en.wikipedia.org/wiki/Type_214_submarine
Beam of Type 214 submarine is 6.3m (General characteristics).

[4] from https://ameblo.jp/calorstars/entry-12157790493.html (above) the lower 2 pictures show the installation of the 2 side-by-side diesels into a South Korean Son Won-II (Type 214 variant). These pictures show the tightness of the diesel section [which may be adequate if South Korea's Son Won-II 's are only used for short missions, close to South Korea's naval bases.]

[5] (see an Oyashio engine room below) For Japan's medium range mission Oyashio and Soryu class submarines there is more space (perhaps >400mm) between the 2 diesels than in the South Korean Son Won-II/Type 214 engine room in [4]. This permits a higher level of maintenance at sea in the Japanese submarines.

[6] http://japanese.china.org.cn/politics/txt/2012-09/16/content_26536166_12.htm (above) Inside the diesel section of a Japanese Oyashio class submarine. The double hull structure consists of an outer light hull (diameter 9.1m) and inner pressure hull (approximately 7.2m?) for the diesel section. A KAWASAKI diesel is on each side of the metal walkway. 12 square-shaped dark metal cylinder head covers can be seen. 

For Japan's newer generation Soryu submarines 2 x KAWASAKI 12V/25/25 diesels are installed, with a bore of  250mm. The width of the passage is approximately 1.2 m which is considerably bigger than those of a Type 212A [2] or the Walrus sub's crowded and dangerous (?) engine room [1]. 

A larger space for the diesel section facilitates maintenance of diesels during the long mission (such as 10 weeks) of an oceanic submarine [like Australia's Collins class. With the Collins having 3 diesels but only within a beam of 7.8m is the Collins' engine room crowded?]

Mainly Anonymous (and Pete)