CONFIDENTIAL REPORT 2G-21
S29
     
 
FORMER GERMAN SUBMARINE TYPE XXI
 
 
 
 
WEIGHT, STABILITY AND INTEGRITY
 
     
 
SUMMARY
 
     
  GENERAL  
          The vessel is designed primarily for submerged operation.  External main ballast tanks and normal fuel oil tanks (but no fuel ballast tanks) are provided, together with bow and stern buoyancy tanks, and regulating tanks.  No negative tank is provided, although one is shown and described in plan and text material available.  External trim and WRT tanks are provided, and added compensation is provided by internal poppet valve tanks.  
          The contents of this section will describe the aspects in which this vessel type differs from earlier types.  
     
  Weights, Displacement and Stability  
          Specification weights for the vessel are as follows:  
 
S I
4
  Pressure Hull Plating
179.60
Ship-
5
  End Bulkheads
9.39
building
6
  Pressure Hull Frames
36.06
Work
7
  Pressure Hull Bulkheads
16.32
 
8
  Machinery Beds and Foundations
25.47
 
9
  Pressure Hull Platforms
40.90
 
10
  Inside Tanks
9.97
 
11
  Outer Hull Plating
66.55
 
12
  Stem, Stern & Struts
9.53
 
13
  Rudders and Planes
11.33
 
14
  Outer Hull Frames & Bulkheads
57.94
 
15
  Superstructure
10.68
 
16
  Pressure-tight Outside Tanks
61.99
 
17
  Insulation, Lagging
1.50
 
18
  Conning Tower
10.56
 
19
  Ordnance Foundations
(in group 15)
 
20
  Torpedo Arrangement
3.23
 
21
  Hawse Pipe
----
 
22
  Communications Arrangements
0.14
 
23
  Arrangements for Personnel
0.12
 
24
  Keel
(in groups 4,11,16)
 
25
  Lifting Arrangements
----
 
     
 
- 1 -
 
     
     

 

     
     
 
  REPORT 2G-21
S29
     
 
S I
26
  Arrangements for Machinery Systems
9.06
Ship-
27
  Brackets & Mounting Plates
2.51
building
  Welding
12.00
Work
   
_____
 
   
573.85
 
   
S II
1
  Bulkhead Closures, etc.
7.40
Ship-
2
  Railings
0.09
fitter
3
  Ladders
0.38
Work
4
  Portlights
----
 
5
  Cleats & Chocks
0.01
 
6
  Flood & Drain Arrangements
11.81
 
7
  Rudder & Plane Arrangements
6.15
 
8
  Armament Arrangements
1.02
 
9
  Anchor Arrangements
0.34
 
10
  Torpedo Arrangements
11.24
 
11
  Ship Control Arrangements
0.08
 
12
  Ballast Tank Arrangements
5.09
 
14
  Arrangements for Crew
2.30
 
15
  Safety & Rescue Arrangements
1.41
 
17
  Miscellaneous Arrangements
3.27
 
   
____
 
   
50.59
 
   
====
 
   
S III
1
  Shielding, Insulation (Heat)
2.25
Joiner
2
  Arrangements for Officers & Chiefs
0.95
&
3
  Arrangements for Petty Officers & Men
0.75
Sheet-
4
  Miscellaneous
2.10
metal
   
____
Work
   
6.05
 
   
====
 
   
S IV
1
  Painting
6.00
Painting,
2
  Cementing
----
etc.
   
____
 
   
6.00
 
   
====
 
     
 
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  REPORT 2G-21
S29
     
 
S I
   
573.85
S II      
50.59
S III      
6.05
S IV      
6.00
       
____
Total hull groups
636.49
       
====
 
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
 
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  REPORT 2G-21
S29
     
 
M I
1
  Diesel Engines
37.10
 
3
  Circulating Water System
4.99
 
4
  Lub. Oil System
2.77
 
5
  Fuel Oil System
3.91
 
6
  Diesel Air & Exhaust Gas System
16.00
 
7
  Shafting
35.89
 
8
  Propellers
1.52
 
9
  Main Motors
29.09
 
10
  Switching System
5.40
 
12
  Electric Wiring
6.41
 
13
  Battery
235.85
 
14
  Battery Venting System
3.02
 
15
  Machinery Compt., Flats, Ladders, etc.
0.05
 
   
____
 
   
382.00
 
   
====
 
   
M II
1
  Rudder Gear
1.67
 
2
  Windlass System
0.11
 
3
  Compressed Air System
21.67
 
5
  L.P. (Exhaust Gas) Blow System
3.99
 
6
  Main Drain Pump
2.14
 
7
  Aux. Drain & Trim Pump
----
 
8
  Heating (where steam) & cooking systems
0.44
 
9
  Fresh Water Still System
0.49
 
10
  Compt. Ventilating
10.18
 
12
  Torpedo Heating, Ventilating & Setting
2.81
 
     
 
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  REPORT 2G-21
S29
     
 
M II 13   Periscope Systems
4.92
  14   Ships Lighting
0.57
  15   Searchlights
0.01
  16   Ship Control Systems
0.01
  17   Command & Announcing Systems
1.37
  18   Voice Tube System
0.37
  19   Signal System
5.74
  20   Emergency & Rescue Arrangements
----
  21   Refrigerating
0.91
  22   Hydraulic System
6.40
  23   Aux. Generator
----
  24   Aux. Switching System
1.76
  25   Electric Wiring
6.03
  26   Shop Equipment
0.65
       
____
       
73.22
       
====
       
MIII 1   Machinery Tools & Parts
----
  2   Electric Tools & Parts
----
  3   Machinery for Ship's Boat
----
       
____
       
----
       
M I      
382.00
M II      
73.22
M III      
----
       
____
Total machinery weights
455.22
       
====
 
     
 
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  REPORT 2G-21
S29
     
 
        Ballast reported by ballast stowage plans amounts to 175 metric tons (see German plan 21S850.132B, Übersicht zur Ballaststauung), but this has, in the case of U-2513 been found insufficient.  Actual ballast on U-3008 when docked amounted to 180 metric tons distributed as shown on Portsmouth Plan 44226.  A heavy spar concrete was used in lieu of other material for ballast.  A check of the vessel against available curves indicate that about 40 tons additional weight is necessary to make a dive when all fuel oil tanks and variables are filled.
 
          Ordnance weights are unknown.  
          Displacement figures from Navtechmiseu report are as follows:  
 
Surface
1621 cu. meters
Submerged
1819 cu. meters
Submerged volume including free flooding spaces
2100 cu. meters
 
          The center of submerged displacement, according to the Calculated Contents of Tanks and Bunkers (Gerechnete Inhalte der Zellen und Bunker des Auszenschiffes) Plan No. 21S 850.123 E/2, is 35.60 meters forward of frame 0.  This is in the control room, about 2/3 of the way aft from the forward bulkhead.  
          Specified surface and submerged GM is:  
 
Surface minimum
290 mm
Submerged minimum
320 mm
 
          Tank volumes and moments are as follows:  
 
Volume in cu. maters
Moment in meters
Flooding area in sq. meters
Venting area in sq. meters
Vent Valve Operating Gear
Flood Valve Operating Gear
Stern buoyancy
14.35
- 29.5
1.44
.03
hand
none
NFO 1a
30.01
- 26.34
Compensating
none
none
NFO 2a
66.72
- 21.22
Compensating
none
none
MBT 1
31.08
- 13.15
3.88
.252
single valve and air piston P&S
none
NFO 3a
65.62
-10.46
Compensating
none
none
NFO 4a
17.46
- 4.29
Compensating
none
none
MBT 2
42.30
- 4.29
3.88
.175
single valve and air piston P&S
none
NFO 5a
14.84
+5.07
Compensating
none
none
 
     
 
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  REPORT 2G-21
S29
     
 
Volume in cu. maters
Moment in meters
Flooding area in sq. meters
Venting area in sq. meters
Vent Valve Operating Gear
Flood Valve Operating Gear
MBT 3
39.92
+ 5.04
3.88
.175
Single Valve and air piston P&S
none
NFO 6a
32.64
+ 9.94
Compensating
None
none
MBT 4
50.80
+13.26
.252
Single Valve and air piston P&S
none
NFO 7a
37.08
+20.06
Compensating
None
none
MBT 5
37.24
+29.59
3.88
.175
Single Valve and air piston P&S
none
Bow Buoyancy
12.11
+31.38
1.64
.110
Single Valve and air piston
none
Regulating
25.12
- .94 )
.03 to
(.002
hand
hand
    bunker              )
either
       (    
Regulating
19.24
+1.60)
or
(.002
hand
hand
    tank
         )
both
       (
 
     
          Each half of each MBT has a separate vent valve. Operating gear for port and starboard halves is in parallel, but it is possible to segregate either side if desired.  When vent valves are power operated from the L.P. air system, the gear for MBT 1 and 2 is controlled by one air valve, that for MBT 3 and 4 by a second air valve, that for MBT 5 by a third, while a fourth controls the bow buoyancy vent.  
          The stern buoyancy tank vent is operated by hand from within the after compartment.  
          High pressure blow lines are fitted to the main ballast and the two buoyancy tanks.  
          Low pressure (Exhaust gas) blow lines are fitted to the main ballast tanks.  
          For trim control, trim tanks, WRT tanks and poppet tanks (torpedo untertriebzelle) are provided.  
          Forward trim tanks have a total capacity of 7.10 cu. meters and a forward moment of 24.79 meters.  After trim tanks have a capacity of 7.20 cu. meters and an after moment of 28.71 meters.  
     
 
- 7 -
 
     
     

 

     
     
 
  REPORT 2G-21
S29
     
          The WRT tanks have a total capacity of 27.30 cu. meters and a forward moment of 19.42 meters.  
          The poppet tanks come in three pairs.  Capacity of each tank and forward moment is as follows:  
 
No. 1 and 2, each .54 cu. meters, 24.89 meters
       3 and 4    " .50  "       " 25.53     "
       5 and 6    " .51  "       " 26.32     "
 
          The water content of a flooded torpedo tube is not known.  The content of each poppet tank approximates the difference between the weight of the torpedo and the weight of the water displaced by the torpedo.  
          In addition to the foregoing tanks, the vessel is equipped with internal collecting and gravity service tanks, fresh water tanks, battery water tanks, sanitary and lub oil tanks, each of which is discussed under its appropriate system.  
          The total fuel oil which can be carried with all suitable tanks filled is 295920 liters.  
          The total lubricating oil which can be carried is 16430 liters.  
          The total battery water is 1555 liters.  
          Drinking water is 6030 liters.  
          Wash water is 582 liters, excluding the WRT tanks, which can also be used to carry wash water.  With WRT tanks, the total becomes 14220 liters.  
          Sanitary tank capacity is 1680 liters.  
          No safety or negative tank is provided.  The space occupied by the negative tank was used as a fuel tank to augment the normal maximum fuel oil capacity.  Capacity of the tank is 14700 liters.  
          According to the Preliminary General Information Book (Vorlaufige U-Bootskinde für U Boote Typ XXI), MBT 1 to 4 inclusive are located low on the sides of the vessel to provide protection from machine guns when the vessel is surfaced, the buoyancy tanks serve as a substitute for the somewhat reduced main ballast tanks and reduce pitching; MBT is arranged to permit venting inboard.  
     
 
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  REPORT 2G-21
S29
     
          Also from the same source, flooding the regulating tanks serves to eliminate buoyancy remaining after ballast tanks are flooded, and the tanks permit compensation for different densities of sea water.  
          Damage control information is also obtained from the General Information Book.  Therein can be found mush the same information as that described in the X-B report.  Points covered are:  
          a)  Weight and trim changes resulting from damaged tanks and compartments when the vessel is surfaced.  
          b)  Inability to compensate for any flooded compartment when submerged except the conning tower or the after compartment.  
          c)  Volume of air in banks is sufficient to blow all main ballast tanks at 70 meters depth.  
          d)  Buoyancy and moment obtainable by blowing fuel oil tanks by way of the compensating water lines (a slow process).  
          e)  A list of bulkhead closures.  
          f)  Characteristic curves for surface and deep drain pumps.   
          g)  A list of the contents of the damage control kit, in which 2 pounds of oakum is added to the items listed in the X-B report.  
          h)  A list of timbers and planks stowed in each compartment.  
          i)  How to flood each compartment in order to escape therefrom.  
          j)  A list of emergency lights (hand lanterns and flashlights).  
     
  Draft and Trim  
          Vessel dimensions from Navtechmiseu report No. 312-45 and General Information Book are as follows:  
 
L.O.A.
251' - 10"
Maximum beam
21' - 8"
Depth from bottom of keel to superstructure deck
25' - 4"
Maximum diameter of pressure hull
17' - 5"
Mean draft
20' - 4"
     (The calculated drag at this mean draft is 43")  
 
     
  Inclining Experiment  
          One has been made on U-2513 in this class.  Values obtained were as follows:  
     
 
- 9 -
 
     
     

 

     
     
 
  REPORT 2G-21
S29
     
  Stabilizing  
          Two fins are built out horizontally from the hull at the after end of the vessel, enclosing the propeller shafts and continuing outboard to a point out from the centerline of the vessel.  Their purpose is to provide adequate stability at high submerged speeds.  On U-3008 and U-2513 they do not extend out as far as the ones shown on German plans or other illustrative matter.  
     
  Rolling and Pitching  
          The vessel is designed primarily for submerged service, and sea keeping qualities as a surface vessel are not as good as those of earlier classes.  Her long deep shape, the pronounced tumble-home topside and the low surface GM lead to pronounced rolling.  She is also reported to be wet.  
     
  Workmanship  
          Workmanship was inferior to that on earlier vessels.  Tolerances on section butts which it was commonplace to hold at the American yard which most nearly approximated the German assembly method were found impossible to attain, and the hulls of the two vessels both have places where one section has been drawn in to meet the next section.  Further, the character of the tank structure brings about many places where access is restricted, and welding at such places, and elsewhere out of sight, is definitely not good.  Undercutting and incomplete welding have both been observed.  
          Here, too, as on previous classes, the work of one group has been in part vitiated by the work of another group.  This phase is discussed under the heading of the systems affected.  
     
  Strength of Hull  
          The hull was designed for a submergence depth of 135 meters (442 ft.) with a safety factor of 2.5 on collapse.  Actual pressure tests on a large scale model resulted in collapse of the lower portion of the figure 8 hull at a pressure equivalent of 900 ft., as reported by the Germans.  
          Further, while the WRT and trim tanks are considered as external pressure tanks, and while the former is exposed to sea pressure when flooding, the bulkhead at the after end of  
     
 
- 10 -
 
     
     

 

     
     
 
  REPORT 2G-21
S29
     
  the WRT tank, separating it from the forward battery, appears to be designed for no more than 73 psi pressure, while the bulkhead separating the WRT tanks from the forward trim tanks is only satisfactory for 107 psi.  
     
  Tightness Tests  
          Tests were, as usual, extensive and elaborate, but there is great discrepancy between test information from different sources.  It would appear that tests given in the specifications could not be, or at any rate were not, met by design in certain cases, and that tests were later modified.  A sample will demonstrate:  
 
Test pressures given for the WRT tanks are as follows:
Hull specifications 284 psi
General Info Book 356 psi
Diving Systems Instruction Book 356 psi changed to 486 psi external, changed to 106 psi
 
          This picture of indeterminability extends through all the available text and plan material.  In view of this fact, it is very difficult to evaluate the expected relationships between test and working pressures.  The confusion evident in the changes made hinders analysis.  It is believed, however, that the general tendency was to test to about 50% over the working pressure, except where a limit was placed by the type of unit employed.  
     
  Hogging and Sagging  
          No specific information is available bearing on this point.  
     
  Riveting and Bolting  
          Comments remain the same as those on the 9C report.  
     
  Comment  
          The vessel is a radical departure from previous practice, and shows it.  It is to be noted that here, for the  
     
 
- 11 -
 
     
     

 

     
     
 
  REPORT 2G-21
S29
     
  first time, a power-operated bow buoyancy tank vent valve appears.  The vent operating gear, however, is a return to the type used on the type 9 vessels, and the air-on-oil operation which appeared on the type X-B valve gear is here confined to engine clutches although it is shown in the sketch book as being applied to the diesel air induction outboard hull valves.  
          Here, also, the fuel ballast tank no longer exists.  
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
 
- 12 -
 
     
     

 


 

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