Notes on the Type XXI

[Marcello]

I will use this thread to post informations and personal observations on this type of u-boat. I use GWX,Commander, Stiebler patch and Wreford Type XXI mod (plus SH5 water mod and ASDIC MKI)

Speed settings I use
- Transit: 5 knots + surface runs at full speed in foggy/bad weather or when enemy air is relatively light.
- Transit in case of heavy enemy air presence: 4 knots
- Snorting and using the periscope: 3-4 knots
- When looking for targets in the patrol area: 1-2 knots
For reaching and leaving the patrol area I have come to the conclusion that in the game a speed of 5 knots is the best compromise between the various factors.Assuming 100% charged batteries at the start and a 15 minutes snorkel run to replenish air supply it will leave you with about a 70% charge at the end of the daily run; enough to deal with any emergency. Thereafter batteries can be topped again in three hours and half.
Only when I do not plan to engage anything along the way and enemy air is less pressing I will push to 6 knots.
On the surface I will usually run at full speed to minimize diving time, though in the safer areas I may run at standard speed.

In real life ther snorkel was often used at 5 knots, personally I find that the vibrations in the game at such speed are not worth it, however useless the periscope might be to detect aircrafts I still prefer to be able to look around. On the other hand going too slow is not practical as there will be depth keeping issues and you want to minimize snorkel/periscope exposure.

[Marcello]

Crew
AFAIK actual Type XXI crew was something like this

6 Officers Commander, 2 x Watch Officers, Chief engineer, Watch engineer and Physician.
4 Chief petty officers (Diesel, E-Maschinist, Obersteuermann and Funkmeister)
1 Boatswain,
14 Petty officers (2 seem., 8 techn., 2 funktechn. and 2 torpedotechn.)
33 Seamen (12 seem., 16 techn., 3 funktech. and 2 torpedotech.)

Personally however I prefer to cut down the seamen to 28 (10 seem., 14 techn., 2 funktech. and 2 torpedotech) and leave out the physician. This way everyone can be rotated between watch duty and rest or simply kept at rest until needed; in the latter case this means I always have a reserve of men always fresh. Otherwise number can be increased to nominal; the the medical officer however is still better left out as there are only two rest slots for officers and besides they were in short supply in real life.

[Marcello]

Snorkel
Personally I set the maximum permissible wind speed for snorkel use at 13-14 m/s, as it appears that employment at Force 6 might have been possible, if barely. I however limit its use at Force 5-6 to the strict necessary.
While I do not know how well the game handles the matter it is a good idea to keep a close eye to depth to minimize snorkel head exposure to radar. The "è" key (at least in the keyboard I use) will bring you to snorkel depth, slightly deeper than normal periscope depth, which will reduce the amount of manual adjustment necessary. Automatic depth keeping and hovering gear was supposedly fitted to at least some of the boats.

Leros, at least as far late war operations in hot areas are concerned, is a don't go out without item. Observation periscope should be left up for realism's sake but actual usefulness is limited, both in the game and real life.

[Marcello]

Fresh water and torpedo load
The Type XXI was fitted with the same water still of the Type IX. The plant however was not designed to be operated at snorkel depth and to do so would create all the sort of issues with piping, heat management and IIRC contamination of distillate by salt water during pressure drops caused by the snorkel valve shutting off. The XXI water needs, owing to the larger crew and more cells, were also greater than the IX; the XXI would thus have to rely largely on its water tanks. The postwar american reports note that at at US style consumption rates water would have lasted less than a couple of weeks. It could have been stretched further with conservation measures and, according to a source, by using trim tanks for extra storage but if you want to be realistic a prolonged stay in in tropical waters in 1944-1945 is probably not a good idea.
However, U-2511 destination before surrender was the Caribbean, whether the issue had yet to become apparent to BdU or it was deemed manageable for a short stay I cannot say.
The issue was fixable with a properly designed water still, whether the germans were working on that I have not been able to determine.

The XXI ws fitted with enough tubes and racks for 23 torpedoes, but three racks were left empty for moving and servicing the weapons.
There is a mod to simulate this that can be found in this thread . No list of the actual types carried is know but it can be inferred that TIII Lut II would make up much of the load, with perhaps a smaller proportion of passive homing torpedoes (TXI likely) than that carried by conventional U-boats. FAT torpedoes would not be carried (mechanical incompatibility or so I have been told).
Advanced torpedoes were in the pipeline, though of those only the T VII is partially modeled in the game.

[desirableroasted]

Thank you for your notes.

I note that you use Beaufort Scale for windspeed... are you calculating that yourself, or is there a mod out there that reports in Beaufort? Having lived right on the ocean some years, that is how I think about windspeed, and would love to have it in the game.

[Marcello]

I calculate it. No idea if there are any mods.

[Gustav Schiebert]

I usually calculate it as well but you can confirm by checking the windspeed from the Navigator's weather report. 1 m/s is about 2 kts, so the worst weather in game (15 m/s) is about 8 kts, which looks right to me.

[desirableroasted]

Yes, the navigator reports m/s, which is also how I think about wind after so long in Europe, but I just thought he stumbled across a Beaufort calculator.

http://en.wikipedia.org/wiki/Beaufort_scale

[Marcello]

Maximum diving depth
The XXI was designed with a theoretical crush depth of 330-340 meters, a design depth of 135m with a safety factor of 2.5. However structural issues, such as the way the bottom pressure hull was joined to upper one and workmanship problems meant that this could not be attained, joining two sections for example required a continuos weld taking about 8 hours to complete that could not be interrupted without creating weak spots
(not good news in 1944-1945 for reasons that will be obvious...) .
Some of these issues were being addressed, for example assembly was going to be moved in special bunkers, but nervethless various studies and estimates put the crush depth to as little as 245 meters or at most just past 300m.
Thus if you want to play realistically the depth gauge, limited at 260m, is pretty much spot on in terms of what you can get away with.
If you instead assume that somehow the design was properly debugged you have in the game at least another 50 meters to play with before taking damage.

[Marcello]

Stern watch station
Some drawings report it but as far I can see from the available pictures its existance is debatable.

[Marcello]

Battery charge
As far as I have been able to find under test condition it took about two hours and half to go from 10% to 60% (1st charging stage), another two hours and half to go from 60% to 90% (2nd charging stage ) and another two hours and half to achieve 100% (3rd charging stage). The third stage stage was used periodically to conserve battery life, in most cases the 2nd would be used. If you are interested in realism not fully regharging the batteries every time might be an interesting addition to gameplay.

[the dark knight]

Originally Posted by Marcello

Stern watch station
Some drawings report it but as far I can see from the available pictures its existance is debatable.

I would agree. I have never seen the stern watch station in pictures. Perhaps a few of the Type XXI's had them, but it seems like most did not.

[Marcello]

Alberich
As far I can tell, whatever plans might have existed to fit the XXI with Alberich coating were in the realms of wishful thinking. Rubber was a scarce material in wartime Germany and would have likely remained so under any circumstance (even in case of a victory against the USSR probably). As far I have been able to find out the priority, aside from the experimental vessels, was to use whatever could be produced for the Type XXIII and the Type XXVI. In practice only some of those would probably fitted with it and only a XXIII was actually equipped.

[Tupolev]

Was the planning to coat the entire hull with Alberich or just the mast heads of the scopes and Schnorkel?

Or am I thinking the radar coatings?

T

[Marcello]

The radar absorbing coating was applied ony to the snorkel head. Earlier in the war the possibility of applying such materials to the tower for surface operations had been investigated but it was quickly realized that the radar signature could not be reduced to a sufficient degree. Materials were either Buna (the synthetic rubber of Auschwitz fame) mixed with iron oxide powder or alternatively a somewhat more complex layered structure using carbon black, foam and paper/plastic. Not sure what combination of both was actually deployed.
Alberich was made up of Oppanol (again sysnthetic rubber) tiles with air cavities to absorb sound, both ASDIC pulses and the u-boat machinery. Naturally since the whole boat had to be protected from both the coverage had to be pretty much complete. This unlike the snorkel RAM meant a lot of material, carefully applied and probably rather maintenance intensive. A small, frequent turnaround boat such as the XXIII must have been somewhat more manageable.