Type IXD2's 23700 NM does not compute!

[Ducimus]

Something about the IXD2's often cited 23,700 NM @ 12 kts has always striked me as incredible.

I noticed wiki's article says: 12,750 nmi (23,610 km) at 10 knots.

Everywhere else says: 23,700 NM @ 12 kts.

But this is wiki were talking about, and not really considered a reliable source. But, it got me looking more closely. Now according to uboat.net:

an IXC is:
76.7 meters long, 6.7 meters wide, goes 13450 @ 10 kts, for 1540 total displacement.

an IXC/40 is:
76.7 meters long, 6.8 meters wide, goes 13850 @ 10 kts, for 1545 total displacement.

An IXD2 is:
87.6 meters long, 7.5 meters wide, goes 23700 @ 12 kts, for 2150 total displacement.

So.....
-an IXC/40 is only 0.8 meters wider, and 5 tons heavier then an IXC.

-an IXD2 is 10.9 meters longer, 0.7 meters wider, and 605 tons heavier.


So with an extra 605 tons, the extra range almost seems plausible....almost. But the thing is, i doubt all that 605 tons was occupied by fuel. IXD2's had two smaller backup engines normal type 9's didn't carry for example. So it still seems like quite a big jump in range.


--------------

Now compare the IXD2, with an equivlant long range attack submarine that could be thought of as a valid comparison.

So here's the IXD2 again:

- 87.6 meters long, 7.5 meters wide, goes 23700 @ 12 kts, for 2150 total displacement.

Followed by a Gato class:

- 95 meters long, 8.3 meters wide, goes 11000 @ 10 kts, for 2424 total displacement.

Mind you both of these boats carry 24 torpedos.

So a gato is, 7.4 meters longer, 0.8 meters wider, and is 274 tons heavier.

Now with wartime modfications of fuel ballast, a gato could go around, im guessing, 13,000 NM give or take. Even then with that additional range, internet sources (which tend to copy each other) mean to tell me that the TypeIXD2 that is 7.4 meters shorter, 0.8 meters skinner, and 274 tons lighter could go an additional 10,700 NM?

I find that a hard pill to swallow, also could it be more then a coicidence that 23700 kilometers converts to 12797 nautical miles? I strongly suspect that somewhere, some source mistakenly cited the KM range as a NM range, and the same mistake has been quoted all over the internet.

Anybody have some hard resources not on the internet to support or refute my hypothesis here?

[Gorshkov]

Not so long ago I posted here Type IXB performance data taken from real commander's KTB entry found on U-boat Archive web-page. Look for some Type IXD2 U-boats KTBs there...maybe similar data were also made. Well, there were not so many Type IXD2 U-boats commissioned - only 29. Have a nice reading...


Speed measures and distances travelled (as for IXB in 1939):

- Cruising speed at 10 knots: 6 days 15 hours 36 minutes = 1596 nm
- Cruising speed at 9 knots: 21 days 14 hours 58 minutes = 4670.7 nm
- Chasing speed at 12 knots: 2 days 5 hours 33 minutes = 642.6 nm
- Chasing speed at 14 knots: 4 hours 35 minutes = 64.25 nm
- Chasing speed at 15 knots: 2 hours 32 minutes = 38.0 nm
- Submerged speed about 2.5 knots: 3 days 1 hour 46 minutes = 64.4 nm

http://www.uboatarchive.net/KTB37-2.htm

[lurker_hlb3]

"The Encyclopedia of Uboats, From 1904 to Present" by Eberhard Moller & Werner Brack

Page 103

Range 13450nm at 10kts / 63nm at 4kts

[Jan Kyster]

Lüth (U-181) reported to have 200 cbm fuel left for the return trip from well east of the Cape to Bordeaux, France = more than 5800 miles

Full tank 605 cbm, so a total of more than 17400 miles possible. Or 26 weeks....
Speed not mentioned.

Source:
Jordan Vause: U-Boat Ace, The Story of Wolfgang Lüth

Btw. found a sea distance calculator: http://e-ships.net/dist.htm

[etheberge]

No that it's the Bible or anything but Clay Blair's The Hunters 1939-1942 says 24000 miles and he specifies that the IXD had double the fuel capacity as the IXC.

In my copy it's on page 501, in the footnote related to the first mention of U-177.

[Ducimus]

Ok... so .. one source says one thing.
Another source says another thing,
and we have an extrapolation right smack in the middle.


Side note. I do wonder what Blair's reference was. Saying a boat has twice the fuel of the previous class of a long range boat is one hell of a claim.

[etheberge]

Yes it's perplexing, it looks like you stumbled into quite the historical mystery.

Blair has a HUGE list of sources in the last volume (40 pages, very tightly packed ) but since the footnote in question isn't linked with one particular source I guess there's no way to know where the info came from.

[etheberge]

Found something in the British Admiralty Intelligence Division Report on Interrogation of U-Boat Survivors, dated June 1944.

Section One details information on all U-boat specs, page 12 is for the IXD2.

The reports says 25000m@10kts with 475t of fuel, as opposed to 10000/15000m@10kts with 139/216t of fuel for the IXC variants.

There seems to be a lot of other good stuff in that report too.

http://www.uboatarchive.net/CumulativeEdition.htm

[Reece]

In the book "The Encyclopedia of U-Boats" (Page 103) has the following on IXD2:
Speed: 19.2/6.9kts
Range: 13,450nm at 10kts/63nm at 4kts

[GerritJ9]

H.T. Lenton's "Navies of the Second World War: German Submarines Vol.1" page 107 states:
O.F. 442 tons; 23,700/57 miles at 12/4 knots.

The German "Geschichte des deutschen Ubootbaus" by Eberhard Rössler gives the same figures for range on page 452, though does not state fuel capacity.

One thing to remember is that diesel-electric propulsion is less efficient than pure diesel propulsion- there are, first, electrical losses in the generator, then electrical losses in the electric motor; pure diesel propulsion does not have these losses. So, assuming the same propeller efficiency and same fuel load, a diesel-electric vessel will have a lower range than the diesel-only vessel.

[GerritJ9]

Another thing to consider is hydrodynamic resistance. The Gato's Length/Breadth ratio (L/B) is 11.44, the IXD2's is 11.68- which would indicate a slightly lower resistance for the IXD2. There are, of course, more variables than simply L/B ratio- block coefficient, underwater hull shape, surface smoothness etc. etc for which I have no figures- nor do I have any figures for tank tests.
Then there is propeller efficiency- are the Gato's props more efficient, equally efficient, less efficient? What about auxiliary load- this burns fuel too! Air conditioning, radar, and all the other electrically-powered goodies the Gato had and which the IXD2 lacked increase the sub's effectiveness as a weapon- but they also cost fuel. If the IXD2's auxiliary load is, say, 200 kW but the Gato's 300 kW, then the extra 100kW means less range on the same fuel load.

[GerritJ9]

I have approached the range question from another angle. Published performance figures state the IXD2 required 5,400 hp (presumably metric horsepower) to reach a speed of 19.25 knots. This translates to 1,308 hp for 12 knots. Assuming a total engine efficiency of 35%, the combustion cycle requires 3,737 hp, or 2,477 kW, to actually produce those 1,308 hp at the shaft. This comes from the fuel, which would have an energy content of about 42,000 kJ/kg. So, per second 0.0590 kg of fuel is used- or, 212.4 kg/hr or 5098 kg/24 hrs. With 442 tons of fuel, this translates to 86.7 days- or 86.7 days x 12 knots x 24 hours = 24,969.6 miles. So the range of 23,700 miles is quite possible. The discrepancy between the 24,969.6 and 23,700 miles is presumably caused by the fuel requirement for auxiliary purposes (or perhaps a slightly optimistic assumption for total engine efficiency).

For the Gato, Lenton's "Navies of the Second World War: American Submarines" gives a speed of 20.25 knots with 5,400 hp- presumably not metric hp, so the metric hp figure will be a bit higher. Assuming the figure is metric hp, however, gives a requirement of 1123 hp at 12 knots, suggesting the Gato's hull actually has less hydrodynamic resistance than the IXD2's, or a better propulsive efficiency, or both. Fuel capacity is listed as "389 tons except SS.228-235 & 275-280 378 and SS.236-239, 265-274 & 281-284 464 tons." Unfortunately no range figures are given. Assuming the range figures posted by Ducimus are correct, then the only explanation for the Gato's lower endurance per ton of fuel is the very large demand made by the Gato's auxiliary load (air conditioning, radar etc).

[TheBeast]

From sources I have read, I really do not think you can compare a US Sub to a German. US Boats had a lot of extra's like multiple toilets and shower for example. German boats had a single toilet for the entire crew and no showers. German boats were more of a pure war machine, with little concern about personal hygiene, focusing on the mission they were being designed for. I read some where that the British called U-boats "Skunks" because they smelled so bad and if one surrender, being sent inside one was almost considered punishment.
I've only been playing SH4/5 since January 2010 but I have done a lot of reading since that time. I have many questions and every day I read more, specially when I think something is not right on my boat. Like Sonar not working while surfaced. If I get a equipment upgrade specifically designed to work while on the surface, why is it disabled while I am surfaced???

[Ducimus]

From sources I have read, I really do not think you can compare a US Sub to a German.

With the IXD2, i think you can, but only with the IXD2.

Here's something that occured to me last night, but I didn't post it cause i was curious as to what people would write.

From earlier discussions along a simiar theme, Luke cited that the Tench class, was built with fuel ballasts, (as opposed to adding them later). Luke said the tench had a range of 16,000 NM @ 10 kts. I don't know what Lukes source was, but i'll trust him in that it's correct.

Navsource.org says two things of interest along with that bit of information.

The balao has 94,400 gallons of fuel for a range of 11,000 NM.
The tench has 113,510 gallons of fuel for the same range. Which makes no sense. The difference between the two boats in fuel is 19,110 gallons. So insert Lukes figure of 16,000 NM here, which would.

In other words, in theory, 19,110 gallons of fuel is responsible for an extension of range by 5,000 NM.

Now according to Dietrich Hille, ex Leutnant (Ing), who served on U-181, U-181 carried 500 CBM of fuel (450 tons).

http://www.singapore-ww2-militaria.c...on%20U-181.pdf

(Page 2) Interesting read, i suggest D/L that

So doing the conversions.
- 94,400 gallons on a balao equals 357 CBM.
- 113,510 gallons on a Tench equals 430 CBM.

Now comparing:

The Tench (430 CBM) 16,000NM, with the Balao (357 CBM) 11,000 NM, we have a difference of 73 CBM of fuel. So in theory, 73 Cubic meters translates to 5,000 NM range.

The 9D2 (500 CBM) with the Tench ( 430 CBM ), we have a difference of 70 CBM. So in theory, we could add just under 5,000 NM on top of the 16,000 NM of a tench, which comes out to just under or about 20,000 NM.

( Of course all of this is disregarding fuel effieciency differences in the engines, hydrodynamics, and drive system gearings and such. So it's one large assumption )

[TheBeast]

Very good reads. Now consider hydrodynamics of each boat. Displacement and Drag, how much power was required to maintain 10knts. Also, I noticed a few posts down about HP and speed. Each increas of 1knt requires more to obtain that speed increase then the speed increase for the previous 1 knot of speed. i.e. To go from 10knts to 11knots may take a additional say 10HP but to go from 11knts to 12knts may take 10.5 HP more. This is the effect of the preasure ridge building in front of the boat pushing all the water a side.
Were you able to find any actual HP stats that specify if Metric?