Tores mailbox VIIC and VIIC/41 operation and technical details

[tore]

Don.
Your last question on the Skizzenbuch.
Page V. I have read your corrections and have following remarks: On page V 2nd section you are still blowing MBT 3 by the vent.
Page VI. 4 th. section you introduce the keel as the weight compensating for the loss of the submarine stability. I am afraid it is a bit more complicated and difficult to explain by just a few words. For a submarine surfacing the center center of buoyancy is moving in relation to the center of gravity thereby the metacentric hight is reduced causing a less stable submarine as it surfaces. As you don`t have a chapter of this theortical elements I suggest you only state the fact the the submarine stability is reduced without introducing the keel which might be confusing.
If you are interested in the theory of the submarine stability I can recommend this link: maritime.org/doc/fleetsub/chap5.htm a very interesting topic.


Tore

[Don Prince]

Hello Mr. Tore,


I found a write-up on the Junkers that explains the piston latching in the outer position...


"Starting is achieved by first locking the pistons in the outer dead position, and then admitting compressed air(at about 500 lb per square inch) to the compressor stages. When the first-stage pressure reaches a certain value (between 40 lb and 50 lb per square inch) the latching gear is
tripped and the pistons are flung together."


The key is they admit HP air to the compressor stages and not the Scavenging air box (a miss-read on my part).  I apologize...


Regards,
Don_

[tore]

Don.
It is easy to get confused on the Junker, anyhow you found the correct answer.
Tore

[Don Prince]

hello Mr. Tore,


I believe the VIIC/41 has a theoretical crush depth of 300 meters with the thicker pressure hull steel plates.  I have only found that the control room plate thickness was changed from 18.5 mm to 22 mm.  Do you know what changes if any were made to the pressure hull thickness of the other 7 sections?


Also, I checked the photo that you provided of the missing depth gauge from U-995 and I can't make out the numbering, but it looks like the maximum depth indication was 250 meters.  If they dived below 250 meters, then were they off the scale, or was a different meter available that indicated down to 300 meters?


Regards,
Don_

[tore]

Don.
I guess the max operating depth for a VIIC/41 was 250 meter hence both the depthgauges,  deep dive- and checking manometers, were scaled to 250 meters. The construction of the pressurehull for increased of max diving depth was mainly due to be able to take evasive depthcharge maneuvres . For the ordinary full circle pressurehull the plating was increased from 18,5 mm to 21mm. The conningtower plating I guess was 32 mm and at the tapered ends of the pressurehull the platethickness was some 3,5 mm less than the full circleplatings. The pressure hull curved endplates were some 35mm , I am not sure how much they were increased on a VIIC/41.
We normally talked about the max. operating depth rather than max. designdepth and if you was at a depth exceeding 250 meters you would consentrate on other problems than the meter being off scale.

Tore

[Don Prince]

Hello Mr. Tore,


The trumplatte was originally 22 mm thick and I got that info from the drawing Uboottyp VII C - Eisenlängsschnitt (1944) that came with Eberhard Rössler's book "Geschichte des deutschen U-Bootbas, Band 1." I don't believe the tower thickness was changed because the diameter of the tower was not as large as the control room.


However, that 1944 General Plan still shows the control room steel plate thickness as 18.5 mm???


The Germans sure didn't pay attention to the little details in the latter war years... and that is a point of confusion for me...


Regards,
Don_

[tore]

Don.
A German; I presume naval architect Køhl, has made a longitudenal drawing of  a VIIC/41 based on, I again presume, a Norwegian drawing (reference Plan 314) unknown to me, where a lot of infos are noted including the plate thickness. I have put up the figures in a table starting from the aft pressurehull frame 0.

  Frame no.         Plate thickness mm                        Distance in mm                       Schuss                         Remarks

    0                         35                                                 0                                         0                               Curved endplate

0-12                        16                                            6000                                           I                             

12- 18 appr.             17                                            3500                                          II

18 app.-27,5             17,5                                         5500                                          III

27,5- 36 appr.           18                                            7100                                          IV

36 appr.-50,5             18,5                                        9100                                            V     Turmplatte mm 22- pressurehull top plate in the tower joint area ( not the towerplating)

50,5-62,5                   18                                           7200                                          VI

62,5-75,5                   17,5                                        7900                                           VII

75,5-81                      16                                           3100                                           VIII     assuming bow curved endplate is 35 mm







The 22mm topplate in the tower area is due to the relative large openings in the pressurehull.


Tore

[Don Prince]

Hello Mr. Tore,


Thank you for the researched data...  I will add the additional info to Skizzenbuch.


Regards,
Don_

[tore]

Don.
A few comments on the diving depths.

Max. diving depth.
The diving depth of a submarine is often confusing as there are many figures mentioned without reference to what the figure represent.

Ther are generally four divingdepth figures.
1. The designed depth.
2. Testdepth.
3. Max operating depth.
4. Crushdepth.

The desinged depth is the theoretical calculated depth based on material, frames , hullopeneings and other physical factors. In this figures the designer includes a safety factor which even can be as high as 2.5
The testdepth is, as it says, the max. depth carried out at the delivery trials and can vary between  the different navies. In US navy I guess it is 2/3 of the designed depth, RN 4/7 and the German navy 1/2 of the designed depth. These depths are normally the maximum depths which the submarines in the different navies are allowed to operate in peacetime.
Crush depth is the dramatic figure used by fiction and movie writers and represents the figures where the pressurehull actually collapses. These figures may vary even for the same class of submarines and depend on the quality and workmanship of the various shipyards.
I remember we were discussing the terrible waste of Operation Deadlight were the German submarines were sunk at deep waters, listning and recording the depth when the crushing sound occurred. Unofficially I read somewhere that the collapsdepths of the VIICs were  varying between 200 and 280 meters. I wouldn trust those figures.
I don`t believe there are any accurate reliable figures and as I said before we did not spend time pondering upon same.
Tore

[Don Prince]

Hello Mr. Tore,


I'm in the process of updating the info on the Papenberg depth gauge and I have a few questions.


Q1. The height of the attack periscope from the keel fully extended is 14.663 meters. When the captain orders the U-Boat to periscope depth; that is 18 meters and then the periscope is fully extended and under cut (below the surface).  Then the U-Boat rises and when the periscope is free (above the surface), then that depth is noted. (U-Boat Diving Manual)...


Q2. Is the papenberg water column source located at the bottom of the keel? I'm not sure?


Q3. Setting up the Papenberg - when the U-Boat ascend to 20 meters using the large depth gauge (0 - 25 m), and then they open the water valve to the Papenberg to establish the water level; then adjust the water column to read 20 meters? I would think that the u-boat's internal pressure +/- would make all the depth gauges inaccurate?


Q4. The scale on the left side displays the residual buoyancy/displacement in metric tons.  On an initial trim test I believe the U-Boat has all the MBTs flooded, the Q-tanks are empty.  The tower would most likely be above the water surface. If the Papenberg inlet valve was opened, then the water level in the tube would rise to some point on the left scale.  If they read the level it should tell them how much water needs to be pumped into the regulating tanks to get to the tower deck awash? or would it be to the tower hatch covered? There is a red marked "0" on the left scale.


I have attached a photo of the Papenberg scales.


Regards,
Don_

[VIC20]

Hello Tore,


Command Room of U 570 has a 3rd sight glass, do you know what its function was?


And what are the discs above the depth rudder control good for?

[Don Prince]

Hello VIC20,


The caption below the photo reads as follows...


"Control Room starboard side forward showing diving plane controllers, hand wheels for manual operation of diving planes, diving plane angle indicators, Bourdon tube type shallow diving depth gauge, closed end tube type "attack" depth gauge, closed loop inclinometers (one with coarse graduations and one with fine graduations), and propeller r.p.m. indicators - Case of deep diving depth gauge is shown at right of photograph - A mechanical diving plane indicator can be seen back of each diving plane hand wheel."


It looks like it's a 2nd inclinometer, one course and one fine...  Perhaps, the disks in back look to be the mechanical hydroplane angle indicators???


Regards,
Don_

[tore]

Mark.
This is indeed a mechanical hydroplane indicator operated by a wire inside a flexible tube, a so called teleflex system.
Tore

[tore]

Don.
Q1. I don`t think there is any standard attack periscope depth. The attack periscope depth is ordered by the CO and may vary depending on light conditions, sea and other prevailing parameters at the time of the attack. I believe the main thing is to hold the boat stable in relation to the surface letting the CO take the small adjustment himshelf.
Q2 and 3. I don`t see the need for going all the way to the keel for the seaconnection for the Papenberg. As long as you have a submerged connection all the time you shall have the waterpressure variables the same whether it is coming from the watersurface down to 14 meters or from 14 meters down to 28. Remember it is the compression of the air in the bufferchamber which is controlling the watercolumn. The adjustment of the Papenberger can actually be done in several ways, all based on adjusting the airpressure in the bufferchamber. F.inst. by having a cock on the top of the chamber letting air out thereby raising the watercolumn, or as the case of U 995 having a draincock at the bottom of the gauge assembly  draining the water thereby reducing the aircompression (raising the water column).As far as I can see the Papenberger on board present days U-995 has a scale which put a 0 depth at the position where the tower wind deflector is breaking the surface, which means 9400 mm from the bottom of the keel. You can of course use any reference point.
Q 4. On the left scale on the U-995 is a sketch showing the attack periscope with depthmarkings, I am not sure the scale shows the residual displacement tonnes. I cannot recall we used the Papenberger for accurate adjustment of the regulating tanks.
Tore

[Don Prince]

Hello Mr. Tore,


Thank you for the update...  The only thing that seems to be a mystery to me is what exactly is the function of the index pointer that slides up and down on the rod on the right side of the Papenberg meter scale?


Regards,
Don_