Type IXD2's 23700 NM does not compute!

[GerritJ9]

I think we can safely overlook any difference in diesel engine overall efficiency- even if there IS a difference, it would be minimal in my opinion, perhaps one or two percent. I'm fairly sure that the different mileage per ton is due to the much larger auxiliary electrical load of the US subs, though I don't have any figures for the power consumption of the auxiliary systems for either IXD2 or Gato unfortunately.

Interesting read by Dieter Hille, by the way! The story about the Malays duplicating a crack in a newly-made bearing is probably quite true- I had a somewhat similar experience in Singapore in the 1970s. The tanker I was serving in required a new section of piping in the deck steam line, so the Chief Engineer arranged for a foreman from one of the local engineering firms to measure the old section. Soon enough two old Chinese men from the engineering firm appeared; the Chief showed them the section to be replaced and instructed them to "Make new pipe same-same old pipe" to which they replied "Yes, Chief, no problem", then proceeded to measure the section with a piece of string (!!!) which one of them happened to have in his pocket.
The next morning a team arrived with the newly-made section of piping, which was a perfect drop-in fit. However.... they had also copied EVERY SINGLE dent, twist and other imperfection- except for the long crack which was the reason for the old section's replacement. Not unnaturally, the Chief was livid, but the foreman said "Chief, you speak make new pipe same-same old pipe, we make new pipe same-same old pipe". In the end the Chief had to sign for work carried out.

[GerritJ9]

For the IXD2 I think we can safely assume the hp figures are metric; the Gato figures are probably Imperial which means the metric figure is higher, but not so much higher that it would cover the difference between the power the IXD2 requires at 19.25 knots and the Gato at 20.25. So the Gato requires less propulsive power for a given speed than the IXD2, though whether that is due to better hull shape, more efficient propeller design or a combination of both I don't know.
Power requirements rise, roughly, to the third power for a given hull- so twice the speed requires no less than eight times the horsepower. Or, 1,000 hp for 10 knots becomes 8,000 hp for 20 knots. This overlooks the decrease in propeller efficiency; as propeller RPMs rise, propeller efficiency drops. On the other hand, engine efficiency rises as load increases so these effects tend to cancel each other somewhat. The net overall effect depends on individual propeller and engine characteristics. For most calculations these effects can safely be ignored.

[Ducimus]

The figures in my last post don't add up either.

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

Here i have to stare at myself in the mirror and ask, "REALLY?!"


If 73 cubic meters of fuel is enough to travel 5,000 NM, then going by that, then 146 CBM is enough to travel 10,000 miles? So where did the rest of the 200 some odd CBM go if looking at the balao?

Seriously, if 70 CBM of diesal = 5,000 miles of travel then, by that logic a balao could travel 25500 NM.


I suck at math and theory crafting.

[Jan Kyster]

"Boat was at sea for a total of 129 days and sailed 21.369 miles. Twelve ships were sunk in the Cape Town-Lourence Marques area for a total of 57.000 GRT."

That is the last entry in the logbook of U-181 after patrol end.
Dated 1700 on 18 January 1943 after U-181 returned from first trip to South Africa and up to Madagascar.



From the Long Patrol...:
19 August. U-181 turning southwest for the cape. 200 cbm left in the tank.
2 September. Cape the Good Hope.
14 October. Entering Bordeaux harbour...

There are several references to 605 cbm and that 200 cbm above gave more than 7500 miles. If that was a third of the tank, then yes. +21000 miles.



One entry regarding The Gun...

From the log book:

"30 November 1943
0600. 80 rounds of 105-mm ammunition have now been fired at a range of 2.000-3.000 meters. About 70 hits aft and starboard side. The inside of the ship is smoking. The boat has only one round of 105-mm left, closes to 400 meters and puts the round after careful aiming into the stern under the waterline. At the same time the 20-mm gun fires explosives rounds into the stern.
0655. Steamer has sunk by the stern. Several bodies are floting around the after deck gun."

[Ducimus]

I'll tell ya what got me chewing on this to begin with.

Was doing a test run in game, and running from France to the cape of good hope, i had used maybe, 10% of my fuel if i remember correctly. At that rate im guessing i could have made Penang, using only 30% of my total fuel capacity. Maybe even less.

That throws up a huge red flag in my mind. No way that was possible. That fuel economy is just too good to be believeable in my mind. Something is not right here. Especially when one considers the game distance is 30% longer then in real life due to a flat map projection.

[Jan Kyster]

I know your motto is "Aiming to Please", but since we all got S3D, why not give her a range you find believable?!

Personally I would trim her for a trip like Germany/France - Cape - Madagascar - Cape - Bordeaux...
That's 32000 km in game ~ 18000 miles plus some = 20000 miles

[Ducimus]

but since we all got S3D, why not give her a range you find believable?!

Yeah. That's true. I'll set it at one of three idea's floating around in my head on what i think it should be. I Just need to test that in game before i commit to any one of them.


Fuel is something of a "weakness" of mine. When it comes to fuel, i can put the most contentious rivet counter to shame, and i'll over analize it tell the cows come home. Any other technical topic, and I'm nowhere near as anal.

[GerritJ9]

Hmmmm.......... I've played the "Evacuation" mission several times (starting from Batavia), running at about 11-12 knots and I've burned a LOT more fuel than 30% by the time I've reached Denmark Strait, more like 50+%. To be as economical as possible, I hardly run submerged up to that point, only diving for about 3 hours whenever I get a warning about radar transmissions being picked up. The approach to Denmark Strait is where it becomes tricky, though. Since the SH4 IXD2 doesn't have a Schnorchel, I run at flank speed to cover as much ground as possible on the surface before I'm actually spotted, then as deep as possible at silent speed until battery or CO2 force me to surface, then flank again on the surface for as long as possible, or battery is recharged (whichever comes first). So far I've only managed to reach Trondheim once (only to be well and truly clobbered on the final stretch to Bergen ), but still had over 10% fuel remaining when I reached Trondheim.
By 1945 refuelling at sea would have been almost impossible, but U-181 could have reached Bergen without refuelling, otherwise she would not have tried to return to European waters.
Using 10% of the fuel to reach the Cape area might be realistic- what speed were you running at, what route? I think the IXD2's most economical speed may be around 8 knots, but unfortunately I can't calculate it without knowing how much the auxiliary load is.

[Stormende]

This is what I found regards the Type IXD2, the source seems very reliable.

I checked the sim file and you are totally right since it got the right speeds but the wrong ranges, since it gives it a max surface range of 23700 @ 10 knots and 57 submerged @ 4 knots and they aren't within specs. To be honest, I do not play much with the IX2D so I didn't even notice it so if I would like it to be as realistic as possible then I will surely alter the file.

http://www.subsim.com/radioroom/albu...pictureid=3587

And while you are into it, check this site, there is useful info regards the engines used by american subs.

http://www.subvetpaul.com/Engines.htm