March 18, 2016

The Bigger The Sub The Longer Its Range?

A World War One Type U-151 U-Boat (U-156 pictured) with an outstanding range/speed of 46,000 km at 10 km/h, 18 torpedos and 2 x 5.9 inch guns, all packed into a snug 1,875 tonnes (submerged). How would it go today? (Courtesy photo end of)
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A comment I've lost was made today along the lines The Bigger The Sub The Longer Its Range

As the writer didn't include links to backup his argument and does not have the knowledge base to make sweeping generalisations, I thought I'd make things easier by disproving "The Bigger The Sub The Longer Its Range"

Submarine

Displacement Submerged
Range Speed Surfaced
Soryu class (2016)
4,200 tonnes
11,300 km at 12 km/h

Collins class (2016)
3,407 tonnes
21,300 km at 19 km/h

Type 214 (Tridente class) (2016)
2,020 tons
22,000 km at 15 km/h

Type XXI  (of World War Two)
1,819 tonnes
28,700 km at 19 km/h

Type U-151   (World War One)
1,875 tonnes
46,000 km at 10 km/h


The Table throws up many issues and inconsistencies but may be a good start for  discussion.

eg. what didn't a sub have much of in World War One?

Pete

17 comments:

Anonymous said...

I-400 (World War Two), submerged displacement 6520tons, range 69450km at 26km/h

Josh said...

Well for one thing, WWI/WWII boats had a completely different hull shape optimized for surface running. So the while the original statement 'bigger the boat, longer the range' is clearly false, any comparison of submerged vs surfaced speed of U boat type hulls vs tear drop hulls is also a moot comparison. US Fleet boats were perfectly capable of maintaining 20 knots where as a modern D/E could manage that for a couple hours at best...but the WWII boats did so on the surface where as a modern D/E would/could only do it under water. Surface speeds are half that, and snort speeds far lower.

Cheers,
Josh

'An interested observer'. said...

Hi Pete, thanks for this. Any possibility of citing sources for the ranges. If these figures are correct, they would certainly blow the Soryus out of the water, and out of contention for the Future Subs, you would think....

Cheers, 'An interested observer'

Anonymous said...

I have doubts on the validity of the statement. After all, a bigger sub leads to overall higher drag due to a bigger and longer tube, requiring bigger engines at a given speed which will be more gaz guzzlers than lesser powerful engines. And then you have a bigger crew needing ever bigger life supports.
KQN

Ztev Konrad said...

Isnt it best to restrict the comparsion to modern submarines, as I dont think they are built with saddle tanks for fuel etc anymore.
Then there is the Collins class, if the longer range was available in the submarines available at the time, why wasnt one of those chosen with just an midsection insert for some extra space.
Then there are the 'declared' capabilities, its hard enough to get technical details of new model planes and their engines to make useful comparisons, while warships have military and in Japans case strong political reasons relating to its self defence laws, for not revealing all what they can do.

Peter Coates said...

Hi Anonymous

Yes, I-400s did have range.

BUT. I-400s would have to be one of the worst subs ever built - really disfunctional aquatic airfields. 18 planned and only 3 built when Japan was reduced to very slender ship-building resources. Hugely vulnerable when launching or retrieving their whole complement of 3 aircraft.

https://en.wikipedia.org/wiki/I-400-class_submarine#Characteristics :

"The I-400-class subs were unwieldy and relatively difficult to maneuver while surfaced owing to their small rudders.[19] The large superstructure also caused the sub to veer off course during any strong wind.[19] The maximum safe diving depth of the I-400-class submarine was only 82% of its overall length, which presented problems if the submarine was dived at too steep an angle in an emergency.[19] Because of their large aircraft hangars and conning tower, all I-400-class boats had significant visual and radar signatures on the surface, and could be detected by aircraft relatively easily. Dive time was 56 seconds, nearly double that of U.S. fleet subs, which made the boats easier to destroy from the air when caught on the surface.[19]

When submerged and traveling at a slow speed of two knots, the offset superstructure forced the helmsman to steer seven degrees starboard in order to steer a straight course.[19] When conducting a torpedo attack the captain had to take into account his larger turning circle to starboard than to port, again because of the offset design.[19] Like other Japanese submarines, crew members in Japanese subs had no air conditioning to control temperatures in tropic waters and no flush toilets.[19] Lack of cold storage and inadequate sleeping quarters greatly limited the crew's diet and forced some of the crew to sleep on the decks [!] or in passageways".

Cheers

Pete

Peter Coates said...

Hi Josh

You answer well the questions in the text: "How would it [WWI sub] go today?" and "what didn't a sub have much of in [WWI}"

The submerged capabilities of all subs in WWI and most in WWII (Type XXI being the honourable exception) was a major difference to sub's today. The greater efficiency of ASW sensors and weapons makes surface running of subs increasingly risky.

So todays subs can stay much longer fully submerged, use snorkel to dicretely semi-submerged and their hull shape preferences prelonged cruising and dash potential when submerged.

BUT getting decent comparative figures for range-speed fully submerged or snorting seems difficult. Range-speed figures SURFACED seem easier to find perhaps because they are less sensitive. A sub in an operational area is unlikely to run on the surface.

Its easier for ASW ships, aircraft and SSNs to wait out an a fully submerged on batteries SSK (like Australia is buying for use up to 2060) and then sink or threaten them when Oz subs need to snort on loud diesel.

Regards

Pete

Peter Coates said...

Hi 'An interested observer'

Sources for the ranges are from Wikipedia with links in the table (meaning much reliance on republished secondary quotes). But as I suggested to Josh these are basically operationally unrealistic SURFACED figures.

If Japan is fair dinkum then Aussie Soryus running on LIBs should be awesome. All to be revealed in about 2033 onwards.

Regards

Pete

Peter Coates said...

Hi KQN

Yes there is no linear relationship between size and range due to higher drag on a larger sub.

Also subs don't automatically have the same percentage of diesel in their displacement. More modern subs may have a higher percentage by weight of batteries and/or AIP for longer submerged running to counter improved ASW sensors/weapons in hotspots.

Modern diesels with more capacity for fast running over a much shorter period also add several variables.

Also none-propulsion, non-fuel items may take up a greater percentage of a subs weight. This includes combat system components workstations/databases/personnel/bunks for them/sonars/other sensors/not just torpedos but Harpoons and maybe Tomahawks (in future).

So while the Type U-151 of WWI (picture up top) had long surfaced range this doesn't mean much with subs built for long submersion today and very much part of the computer information revolution. If you've seen Das Boot WWII its sub sensors was very much one luckless sonarman with a good ear and Kapitan with a small periscope.

Regards

Pete

Ztev Konrad said...

Hi Pete.
What was the Collins requirements that dictated a larger boat than that available from the short ranged European alternatives. We know range was one but what were the others that were volume critical. I understand the engines were just more cylinders. Was the electric motor diameter bigger for a higher speed ?
Regarding the Soryu's public domain figures its very hard to find definitive maximum range at say cruising transit speed

Peter Coates said...

Hi Ztev [19/3/16 8:29 AM]

Its a great opportunity for you to do some research on subs [eg. the Collins] and generate some links for the benefit of others.

Cheers

Pete

Vigilis said...

Hi Pete

The advantage of extended operations sub ranges must consider the eventual need for forward positioned sub tenders for supplies (including chow), repair & other.

Nothing can be more embarassing to the reputation of a modern navy than having to send a tow to Swedish waters, for instance, to retrieve a dead-in-the-water sub.

In such cold war situations unaccompanied submarines disabled on the surface can be particularly prized targets for hostile boarding. Escorting subs would obviously be an inappropiate compromise of mission stealth.

I am reminded of this curious NDTV speculation regarding Chinese nuclear subs:

"The Indian Navy has also noted the deployment of a submarine tender deep in the South Indian Ocean as part of search operations for MH-370, the missing Malaysian jetliner. The presence of this vessel suggests the deployment of a Chinese nuclear submarine far from its shores, something which has not been the norm for China's submarine fleet in the past which has typically operated well within the range of ships and aircraft operating from land bases."

Ztev Konrad said...

Thanks for that tip Peter, Ive started digging and interesting things have come up, but its important to keep it in the context of the new sub program as the Collins previous issues have been well and truely flogged before.
Regarding the increasing size increased fuel consumption tradeoff, its well known that wetted area increases at a slower rate than volume for vessels. Thats why tankers, cruise ships, container ships have all been getting bigger, as they can easily carry the extra fuel required ( increased mechanical efficiency helps) as well as benefit from the increased volume.

Peter Coates said...

Hi Vigilis

Sub tenders are indeed handy for operations at extended range - including for range limited SSKs.

I'm aware of tender https://en.wikipedia.org/wiki/USS_Frank_Cable_(AS-40) at Naval Base Guam. AS-40 has apparently been supplemented and perhaps in future replaced at Guam by https://en.wikipedia.org/wiki/USS_Emory_S._Land_(AS-39) .

AS-39 was previously at Diego Garcia and maybe won't be replaced at Garcia.

Tenders seem so large, hence expensive they are a great power full force support. Probably allies of the US also utilise those tender services

Yes, being a great power, China has also developed a class of tenders - what China calls the https://en.wikipedia.org/wiki/Type_926_submarine_support_ship

I think a Type_926 tender was on hand at least twice in Columbo, Sri Lanka accompanying a Chinese SSK and SSN over the last couple of years. That Chinese tender would likely have ranged all over the Indian Ocean.

Regards

Pete

Peter Coates said...

Hi Ztev [at 20/3/16 10:56 AM]

The Collins problem of choosing the wrong diesel engine for high speed, long transit, leading to low engine reliability, has apparently never gone away. Even the mid-life overhauls to take the Collins subs lives through to the 2030s will not involve replacement with a new, efficient more reliable engine.

Turnbull's decision to prolong the Collins existence and then offer a sky-high $50 Billion for the replacement is typical of Australia's, troubled submarine record.

Certainly if Australia buys the evolved Soryu it will by a submarine tradition of perhaps 20 year life subs that are built (diesel engine and all) around a range of 6,000 nautical miles

Yippee :)

MHalblaub said...

Dear Pete,
German Wikipedia mentions a range of 15,000 nm @ 10 kn for a Type XXI snorkling.

Submerged speed was very close to surfaced speed running on electric motor only.

The Oberons have quite the same shape.

Regards,
MHalblaub

Peter Coates said...

Hi MHalblaub [at 22/3/16 6:12 AM]

Yes indeed https://de.wikipedia.org/wiki/U-Boot-Klasse_XXI

Regards

Pete