Is it not possible to accurately portray the German Type XXI?

[RoflCopter4]

Originally Posted by Subnuts

How fast are you going? The US Navy's official report on U-2513 and U-3008 gives the following submerged ranges: 365 miles at 5 knots on one battery, 285 miles at 5 knots on two batteries, 170 miles at 8 knots, 110 miles at 10 knots, and "one hour" at 17-18 knots.

The entire, rather detailed, report can be read here: http://www.uboatarchive.net/Design/D...iesTypeXXI.htm

I stand thoroughly corrected. I didn't know there were so many problems with the Type XXI. This report is downright scathing. I'm disappointed that this report mentioned almost nothing about the diesels' performance while snorkelling. All of it's figures for submerged speed and endurance are when using the electric motors and batteries. How fast could it go with the diesels when snorkelling? Was it ever intended to do so or were the diesels just meant to charge the batteries? Would it just have run off the electric engines with say one diesel engine up to keep the batteries at full charge?

It also mentions nothing about the length of time required to charge the batteries. From the constant complaining about the low performance of the diesels I could imagine it taking a fair long while, but it doesn't say.

[TorpX]

Battery recharge:

As it is necessary to furnish approximately 1200 HP for 4 hours to the generators for charging each of the two batteries at the normal charging rate, the time required for a full charge is excessive. This necessarily places a major handicap on the vessel's operation and decreases the value of the higher submerged speeds.

As far as maximum snorkeling speed, I doubt they could go above 6 kn., as greater speeds would likely damage the snorkel/linkages.

[ColonelSandersLite]

What torpx said. Snorkeling isn't about maximum speed, it's about not having to surface.

[RoflCopter4]

Ah. Fair enough. Would it be standard practice then to run the battery down with the electric motors, stick up a snorkel, recharge them, take it down, run the battery dead, etc etc? This seems like it would be a problem if you were near the end of a cycle with low battery and suddenly you had to dive. On that note, would the electric motors be propelling the craft even while the diesels were charging the batteries while submerged? Or would you just have the diesels doing both and the electric engines off for the duration of the snorkel?

This doesn't even have to be a theoretical question: what do modern diesel-electric submarines do?

Sorry if this is getting wildly off topic. I've never really understood how the snorkel was used.

[ColonelSandersLite]

U-boats are direct drive, not diesel-electric. In their case, the electric motors are also the generators. They had systems of clutching the diesels and electrics. During economy cruise, one engine would be running in direct drive mode turning the screw, while the electricity generated by the electric motor in charge mode on the same shaft would be used to turn the opposing shaft. In charge mode, the diesel on one side would be running in direct drive mode providing some power, while the opposite engine would be disconnected from the screw and just turning the electric motor in charge mode.

Compare this to a US fleet boat where any one or more of 5 engines can be generating electricity and the screws are always turned by the electric motors.



I can't answer the question about historical SOP, though I very much doubt that it was general practice to run the battery all the way down. More likely they tended to recharge when battery charge was at some specific percent of capacity, or on a time table, or perhaps just tended to run with the snorkel up continuously if the strategic situation allowed.

[Rockin Robbins]

Originally Posted by RoflCopter4

I stand thoroughly corrected. I didn't know there were so many problems with the Type XXI. This report is downright scathing. I'm disappointed that this report mentioned almost nothing about the diesels' performance while snorkelling. All of it's figures for submerged speed and endurance are when using the electric motors and batteries. How fast could it go with the diesels when snorkelling? Was it ever intended to do so or were the diesels just meant to charge the batteries? Would it just have run off the electric engines with say one diesel engine up to keep the batteries at full charge?

It also mentions nothing about the length of time required to charge the batteries. From the constant complaining about the low performance of the diesels I could imagine it taking a fair long while, but it doesn't say.

See, the problem with the Type XXI was that it never had enough people trained to use it that it was used in battle. Therefore, any pie in the sky claim could and would be made about it, much in the same way as the other "super weapons" the Germans designed, maybe even produced a few but never had their limitations tested.

So all we're left with is the grandiose stories the originators used to sell the products to a military starving for stuff that worked! "Crap! We need some weapons bad. Weapons that work."

"Hey we have a future weapon that MIGHT work!"

"Here's the last of our dwindling resources: build it."

A fair plan, executed today, beats a perfect plan to be executed tomorrow. And the perfect plan is only perfect while it's just a dream. And it might not start tomorrow. And....we'd best go with the fair plan and work it to death.

The Type XXI was full of undiscovered flaws and a few of them would have been fatal. A big one was that the snorkel was one incredible radar target. So they'd be sitting there at snorkel depth, deaf, dumb and blind and the bombers would just have a party at their expense. The U-boat would just vanish and the Germans not a bit wiser for the experience. Fortunately for them they were unable to train enough crews for the boats to see action.

[RoflCopter4]

Originally Posted by ColonelSandersLite

U-boats are direct drive, not diesel-electric. In their case, the electric motors are also the generators. They had systems of clutching the diesels and electrics. During economy cruise, one engine would be running in direct drive mode turning the screw, while the electricity generated by the electric motor in charge mode on the same shaft would be used to turn the opposing shaft. In charge mode, the diesel on one side would be running in direct drive mode providing some power, while the opposite engine would be disconnected from the screw and just turning the electric motor in charge mode.

Compare this to a US fleet boat where any one or more of 5 engines can be generating electricity and the screws are always turned by the electric motors.



I can't answer the question about historical SOP, though I very much doubt that it was general practice to run the battery all the way down. More likely they tended to recharge when battery charge was at some specific percent of capacity, or on a time table, or perhaps just tended to run with the snorkel up continuously if the strategic situation allowed.

Interesting. I didn't know. In the latter case do you think they'd have run both diesels turning the shaft and recharging at the same time (or just the shaft as the situation should call for) with the snorkel up or do you think they'd run one diesel recharging both batteries and have the e-machines turning the shafts?

Originally Posted by Rockin Robbins

See, the problem with the Type XXI was that it never had enough people trained to use it that it was used in battle. Therefore, any pie in the sky claim could and would be made about it, much in the same way as the other "super weapons" the Germans designed, maybe even produced a few but never had their limitations tested.

So all we're left with is the grandiose stories the originators used to sell the products to a military starving for stuff that worked! "Crap! We need some weapons bad. Weapons that work."

"Hey we have a future weapon that MIGHT work!"

"Here's the last of our dwindling resources: build it."

A fair plan, executed today, beats a perfect plan to be executed tomorrow. And the perfect plan is only perfect while it's just a dream. And it might not start tomorrow. And....we'd best go with the fair plan and work it to death.

The Type XXI was full of undiscovered flaws and a few of them would have been fatal. A big one was that the snorkel was one incredible radar target. So they'd be sitting there at snorkel depth, deaf, dumb and blind and the bombers would just have a party at their expense. The U-boat would just vanish and the Germans not a bit wiser for the experience. Fortunately for them they were unable to train enough crews for the boats to see action.

You're probably correct, but to be fair, byfar the most precious and rare resource Germany had left to allocate by the end of the war was manpower. They could not afford to lose more men, especially good men. They could have spent all the money and resources they wasted on the V2 rockets on more fighter planes, but who would fly them? Teenagers?

[TorpX]

More about Snorkeling:

This pertains to earlier types, and may or may not apply to type XXI.

Blair emphasized boats did not snorkel all the time. It was hard on the crews, and really wasn't necessary. On the other hand, batteries were not fully discharged either. That would not only risk leaving you with a flat battery at a bad time, but would be wear out the batteries faster.

Since snorkeling made the boat 'deaf', I am guessing they usually snorkeled in the daytime, so they could at least use the periscope, and run deeper at night on the battery, unless they considered it safe enough to surface. However, bad weather could make snorkel use impossible, so maybe they had to use it at night, sometimes.
The danger there is that a plane could home in on the snorkel echo, and attack them without warning.

[RoflCopter4]

Sorry to necro this thread after a month, but I don't know why I didn't reply. I am still curious about this.

The type XXI modelled in Operation Monsun is clearly not some kind of barely cloaked XXIII, it's definitely it's own boat with a lovely model and all. The thing does run for a fair time underwater, and while I haven't tested how far, the big problem with it is the fact that it takes almost two days to charge the batteries under most conditions. I started this thread to ask about that. Is there any data on how long it would normally take? Should it simply be a matter of multiplying engine performance by time to see how long it would take to generate x number of joules for the batteries?

Incidentally you mentioned that snorkeling leaves a boat deaf, blind, and a very blatant target for late war radar. Two questions to that: firstly at what point in the war did allied radar have the ability to see a snorkel from the air? And secondly, didn't the snorkel have a radar detector on it? Wouldn't that give away any aircraft that spotted it?

[TorpX]

Originally Posted by RoflCopter4

Incidentally you mentioned that snorkeling leaves a boat deaf, blind, and a very blatant target for late war radar. Two questions to that: firstly at what point in the war did allied radar have the ability to see a snorkel from the air? And secondly, didn't the snorkel have a radar detector on it? Wouldn't that give away any aircraft that spotted it?

I didn't say snorkeling would make the boat blind, only deaf. If they were using it at night, they would be blind, as well. Not entirely blind, but not able to see aircraft in time.

Don't know exactly when aircraft got centimetric radar; probably later, but not every unit will get the equipment at the same time.

About the radar detectors; my understanding of these is that they were not able to detect the later Allied radar.



About the batteries; I'm not surprised battery performance is lousy. SH4 has a major bug regarding batteries. You should be able to set performance to proper (historical, or whatever desired) levels in the *.sim files, but it just doesn't work. Undoubtedly a mistake in the code somewhere.

TMO and ISP mods (for allied subs) had to use an awkward workaround to achieve sensible battery performance.

[ColonelSandersLite]

Originally Posted by TorpX

I didn't say snorkeling would make the boat blind, only deaf. If they were using it at night, they would be blind, as well. Not entirely blind, but not able to see aircraft in time.

Robins did, not you.


Since this thread died, I had done some more research on it and somehwere I found some german general orders on the use of snorkels. The order was to recharge at the start and end of every night. I'll see if I can't find the link again soon.

[ColonelSandersLite]

Originally Posted by RoflCopter4

Is there any data on how long it would normally take? Should it simply be a matter of multiplying engine performance by time to see how long it would take to generate x number of joules for the batteries?

The answer to that question is found in Subnuts link above:
"As it is necessary to furnish approximately 1200 HP for 4 hours to the generators for charging each of the two batteries at the normal charging rate"

It is noteworthy that the captured submarine could only make 850 hp snorkeling, so charge time would be substantially more. It's not a simple 41% longer either, as a higher proportion of the generated power would be going towards propulsion at whatever speed they where recharging at. At a guess, recharge while snorkeling probably took in the vicinity of 7-8 hours or so. I'm sure it could have been fixed if Germany had more time, but they didn't.

But yes, if it's taking two days, that would be a bug as described by torpex. Someone might have worked around it, I dunno. I would do some searching on operation monsun oriented mods (which I'm almost totally unfamiliar with).

Originally Posted by RoflCopter4

firstly at what point in the war did allied radar have the ability to see a snorkel from the air? And secondly, didn't the snorkel have a radar detector on it? Wouldn't that give away any aircraft that spotted it?

We had centimetric radar on aircraft before the germans even started snorkeling.
DMS-1000 (10cm radar, forward looking only) was operational on liberators in march of 1942.
AN/APS-2 (10cm radar) was operational on american aircraft from feb 1943
AN/APS-15 (3cm radar) was operational on american aircraft from nov 1943

I don't have exact timeframes for the british, but I'm sure it's similar.

From Uboat.net:
The first boat to be fitted with the Schnorchel was U-58 which experimented with the equipment in the Baltic during the summer of 1943 but operational boats didn't start to use it until early 1944 and even as late as June 1944 only about half of the boats stationed in the French bases had Schnorchels fitted.


The only german radar detector that I can remember seeing references to being snorkel mounted naxos. Range wasn't good, less than the range of the radar it was detecting. It was *very* rare as well. I don't think I have ever actually seen a picture of it in operational use. Further, it probably would have been useless vs AN/APS-15, though still could have helped with detecting the older AN/APS-2 when encountered.

A good portion of the problem is that the germans didn't trust their radar warning receivers at all. This stems from a british POW that convinced them that we where homing in on metox signals in august 43. This offered a believable lie to the germans, since we where detecting them with AN/APS-2 that the germans couldn't detect. From their point of view, attacks where just coming out of nowhere and this finally explained why. From that point on, the germans where completely paranoid about their receivers. Later designs reduced emissions, which reduced detection ranges and the captains still didn't trust them so they where often just not used, even when equipped.

A good solid read on the detection/countermeasure war between germany and the western allies can be found here:
http://www.ibiblio.org/hyperwar/USN/...51/ASW-14.html

[nionios]

Originally Posted by ColonelSandersLite

We had centimetric radar on aircraft before the germans even started snorkeling.
DMS-1000 (10cm radar, forward looking only) was operational on liberators in march of 1942.
AN/APS-2 (10cm radar) was operational on american aircraft from feb 1943
AN/APS-15 (3cm radar) was operational on american aircraft from nov 1943

I don't have exact timeframes for the british, but I'm sure it's similar.

From Uboat.net:
The first boat to be fitted with the Schnorchel was U-58 which experimented with the equipment in the Baltic during the summer of 1943 but operational boats didn't start to use it until early 1944 and even as late as June 1944 only about half of the boats stationed in the French bases had Schnorchels fitted.


The only german radar detector that I can remember seeing references to being snorkel mounted naxos. Range wasn't good, less than the range of the radar it was detecting. It was *very* rare as well. I don't think I have ever actually seen a picture of it in operational use. Further, it probably would have been useless vs AN/APS-15, though still could have helped with detecting the older AN/APS-2 when encountered.

A good portion of the problem is that the germans didn't trust their radar warning receivers at all. This stems from a british POW that convinced them that we where homing in on metox signals in august 43. This offered a believable lie to the germans, since we where detecting them with AN/APS-2 that the germans couldn't detect. From their point of view, attacks where just coming out of nowhere and this finally explained why. From that point on, the germans where completely paranoid about their receivers. Later designs reduced emissions, which reduced detection ranges and the captains still didn't trust them so they where often just not used, even when equipped.

A good solid read on the detection/countermeasure war between germany and the western allies can be found here:
http://www.ibiblio.org/hyperwar/USN/...51/ASW-14.html

In RFB-German campaign the description for Metox RWR says that it can be detected although it's a passive device.So should we use Metox or not?And how we can get rid of it:
by switching radar off or by uninstalling it from the conning tower?