CONFIDENTIAL REPORT 2G-21
S42
     
 
FORMER GERMAN SUBMARINE TYPE XXI
 
 
 
 
MAIN REDUCTION GEARS
 
     
 
SUMMARY
 
     
          Two sets of helical type reduction gears for use with the main motors and the diesel engines respectively, and one set of V-belt drives for use with the creeping motors are installed on the XXI.  Previous types have had direct drive propulsion units with no gears or belts.  Disregarding space considerations, the arrangement of the reduction gears appears unnecessarily complicated.  
          Although considerable maintenance and adjustment is required on the V-belt pulley drives, they provide the desired quiet transmission of power from the creeping motor to the main propelling shaft.  
     
     
     
     
     
 
April, 1946
 
 
 
 
PORTSMOUTH NAVAL SHIPYARD, PORTSMOUTH, N. H.
 
     
     
     
 
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  REPORT 2G-21
S42
     
 
MAIN REDUCTION GEARS
 
     
  1.  INTRODUCTION  
          Considerable detailed information on German reduction gear design and manufacturing practices is contained in NavTechMisEu Technical report 357-45.  In this report only a general coverage of the subject will be made to analyze the design features of the reduction gears on the Type XXI.  
     
  2.  GENERAL DESCRIPTION  
          The diesel engine and main motor reduction gears are shown on Plates I and II respectively.  Specific data on these gears is listed below:  
 
 
Diesel Reduction Gear
Main Motor Reduction Gear
Wt. Main Gear (plus shaft)
2050 lbs.
3580 lbs.
Wt. Pinion (plus shaft)
1470 lbs.
595 lbs.
Gear Pitch DIameter
21.4 ins.
53.6 ins.
Pinion Pitch Diameter
21.4 ins.
10.6 ins.
No. Gear Teeth
128
198
Gear Ratio
1.62/1
5.079/1
Tooth Angle
30°
30°
Diametral Pitch
4.23
4.23
Tooth Width
15.7 ins.
16.5 ins.
Length Pinion
40.3 ins.
46.5 ins.
Length Gear
48.5 ins.
45.7 ins.
Gear Eff.
*96.5%
**97.5%
Heat Dissipation
2920 BTU/min.
2520 BTU/min.
Working load on pinion
22000 lbs.
17500 lbs.
Working stress
51000 psi
54300 psi
*    Includes Main Coupling    
**  Includes Vulcan Coupling    
 
     
          Oil pressure at 1.5 "atu" (approx. 21 psi) is used for lubrication.  This is furnished for both gears by a standby gear oil pump prior to running, and by an attached pump on the main motor pinion shaft when the gears are in  
     
 
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  REPORT 2G-21
S42
     
  operation.  
          The thrust of the main gears is taken by thrust shoes that bear on the forward and after surfaces of the gears.  The pinion thrust is taken by thrust collars on the pinion shafts.  A separate thrust collar to restrict movement of the Vulcan coupling is attached to the inner pinion shaft of the diesel reduction gear.  
          The V-belt drive is shown on plate III.  Twelve individual leather V-belts are used.  The tension of these belts can be readily adjusted.  Considerable care is required in order to maintain equal tension on all belts under varying loads, and after prolonged periods of running.  Insufficient belt tension and improper condition of the pulley surfaces can result in slippage of the belts, at time producing excessive noise.  The V-belts normally remain idle (creeping motor clutch disengaged) when using propulsion from the main motor or the diesel engine.  Specific data on the design of this drive is listed below:  
 
Wt. of coupling and pulley
2000 lbs.
Wt. of small pulley
260 lbs.
Outer diameter of pulley
41.8 ins.
Width of pulley
20.0 ins.
Size of belts
1.26" x .79"
Highest shaft RPM
110
Reduction
1 : 2.68
 
     
  3.  CONCLUSIONS  
          The main reduction gears are standard in nature and offer nothing unique in their design.  Herringbone gears are considered more satisfactory than the helical gears used on this type.  Also, it would appear that both speed reductions could have been obtained in one gear with no loss in flexibility or propelling characteristics.  
          The V-belt drive employed for the creeping motor is a satisfactory means for transmitting a low amount of power with a minimum of noise.  However, considerable maintenance is required to retain maximum quiet power transmission.  
     
     
 
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