Translated by: Maciej Florek

     
 
 
 
K  r  i  e  g  s  t  a  g  e  b  u  c  h
  
     
 
" U-107  "
  
     
 
Machine Section
  
 
War patrol from 21.4. to 11.7.1942 (6th War Patrol)
  
     
  A.)  1.)  Diesel power plant failures - cooling water pumps, starboard exhaust gas valve, fuel oil loss, lubricating oil purifier failure.  
          2.)  Aft diving plane failed.  
          3.)  Distilling unit's vapor pump failed.  
          4.)  Trim pump out of service.  
          5.)  Main drain pump buzzing sounds, leaking.  
          6.)  Both negative buoyancy tanks leaking.  
          7.)  Conning tower hatch leaking.  
          8.)  Quick vent valve of main ballast tank 7 starboard leaks.  
          9.)  Battery:  Abnormally heavy water consumption, efficiency heavy degraded.  
        10.)  Junkers compressor failed.  
        11.)  Port head valve multiple leaks.  
        12.)  Minor failures.  
     
  To A 1:  a)  When inspecting the diesel engine cooling pumps on 9, 11 and 13 June, looseness of the retaining brackets of the port pump's inlet valve, and the starboard pump's inlet and output valves was eliminated. On 16 June, knocking noises appeared in the starboard pump.  After immediately stopping the engine an investigation was conducted, which showed the following:
          The retaining bracket was broken and the starboard external inlet valve's seat was badly damaged.  
  Probable cause:  
          Breaking of the valve seat rings. Pump had to be stopped. The repair took 3.5 hours. Otherwise, the new drives (hardened shafts) of both cooling water pumps have been working without any problems.  
                b) Spindle guide, grinding gear and stuffing box of the internal, starboard exhaust valve leaks quite heavily despite tightening.  When the starboard valve is closed during submerged cruise, after cooling down, the water leak in the exhaust manifold is even greater.  The turbo-blower casing and valves must be replaced.  Despite frequent lubrication, the starboard valve is very hard to operate.  Crash diving takes twice as long.   There is water in the cylinders of the starboard engine.  The increasing level of water in the starboard collecting tank over approximately 1% is compensated for by cruising at higher RPM.  On the basis of the indicator diagram and the exhaust's color, it seems that the piston rings must be replaced due to water leaks.  
                c) From 10 to 12 June the following fuel oil loss was determined:  
                Port 1 internal 5 m³ (cause not clear, not used previously, refueling performed normally)  
                Starboard 1 internal, 1.5 m³ (probably leaks during fuel transfer to collecting and gravity tanks)  
                Starboard 2 internal 1 m³ (unexplained)  
  Refueling according to the Flotilla Chief Orders.  Oil flew from the test lines.  Cooling water pump used.  No oil leaks.  
                d)  During last overhaul of the boat in the yard the lubricating oil purifier was exchanged with one taken from another boat.  There is a leak in the loose valve seat ring over the neck journal bearing, and as a result, the bearing, worm gear and the shaft were running in a mixture of the lubricating oil and water. After 24 hours of continuous operation, the purifier stopped with a buzzing noise.  The teeth of the worm gear were broken out for half of their length.  Repair was not possible by on board means.  
     
     
Click the flag to view the above page from the original German KTB
     
 
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                e)  Due to spring fatigue (opened at 0.9 kg/cm² and did not close) - despite immediately stopping the diesel engine - the starboard cooling water safety valve caused a large water intake in diesel engine room.  The spring tension was increased by inserting a 3 mm thick gasket. The repair took 1 hour.  The valve is tight.  
     
  To A 2:  On 3 May the aft diving planes jammed in the “hard up” position due to limit switch failure. The boat was trimmed on an even keel and the limit switch was removed. The switching axle of the switch was rusted and eroded in the stuffing box.  The diving planes spindle was moved to the neutral position by means of tackle and crowbar and a new limit switch was installed. The repair took 8 hours.  
          On 31 May during a submerged attack, the aft diving planes driving motor windings started to smoke. The driving motor was flooded with lubricating oil from the gear box, through the radial shaft seal of the full-floating axle. The commutator sparked strongly.  
          The motor was disassembled, thoroughly cleaned, the resistance of the armature and field windings measured, commutator removed and cleaned, and the brushes replaced.   After lowering the lubricating oil level in the gear box down to the half of the height of the inspection hole, no further failures occurred.   The repair took 30 hours.  The boat had to be submerged to mount the motor, for this purpose, removing of the manual driving shaft gear was necessary.  
     
  To A 3:  On 12 June a buzzing noise occurred in the vacuum pump.  
  Due to slight bearing looseness, the working and control pistons of the pump blocked each other, which led to breaking of the gear teeth of the drive gear and drive shaft at the point of passing through the casing.  After removing both pistons, the pump casing openings were closed with flanges and the evaporator started working as over-pressure distilling unit.  
                                     Overpressure:         0.1 kg/cm²  
                                     Capacity:               100 liters/day  
                                     Salinity:                  6 - 8 mg/liter  
     
  To A 4:  After a short time of operation, knocking noises occurred in the trim pump, similar to those during the previous war patrol, which led to the misaligning of the drive motor and pump shafts (Goal of the repair: aligning the shafts).  Up to 13 June rubber sleeves of the coupling, destroyed by working, had to be replaced 4 times.   On 13 June the bearings of the worm shaft were warmed up to high temperature and knocking occurred.  After lifting and suspending the driving motor, the worm shaft with bearings and worm gear could be dismounted.  Sea water had leaked into the crankcase through a cracked cooling coil.  The worm gear as well as the ball bearings were heavily rusted and corroded.   The bronze worm gear was heavily worn on its edges.  Bronze mud was in the crankcase.  
  The cooling coil was closed with flanges and the ball bearings set up for lubrication with grease. After assembly, the pump was run for a short time without any serious increase in the temperature of the bearings or any loud noise.  It must be considered why the oil can not be exchanged without pump disassembly, if grease lubrication is safe for the ball bearings and the drain screw of the crankcase is so inconveniently located.  The repair took 70 hours.  
     
  To A 5:  On 23 April when starting the main drain pump, especially when submerged and when pumping from pressurized regulating tank, a knocking noise occurred in the separating chamber caused by the ball of the check valve.  The check valve and venting cock must not have been air tight. Multiple grindings of the leaking vent cock and check valve did not remove the problem.  When attaining greater depth, the vent lines has to be wedged with wooden plugs to prevent large water leaks (pump remains under external water pressure, because the main drain pump suction hull valve and intake of the main drain pump are leaking).  
     
     
     
     
 
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  To A 6:  Since 15 May, both negative buoyancy tanks leak.  They flood when external sea water pressure increases; when pressure decreases, they leak or vent outboard.  By pressurizing the tanks or venting them inside the boat, corresponding to the depth, the tanks are made makeshift tight.  
     
  To A 7:  The leaking conning tower hatch admits water until periscope depth is achieved, can not be sealed by setting the hatch dogs in their stop position.  The hatch gapes over ¼ of the perimeter length.  The hatch and the frame must be adjusted precisely in the yard or the frame must be milled.  
     
  To A 8:  On 12 May, while blowing, heavy leaking of quick vent valve chamber 6/7 in the upper deck was discovered.  Part of the rubber seal of the valve disc of the starboard tank 7 was cracked at the external hinge and jammed between the seats.  The valve disc was disassembled and the rubber seal was replaced.  The repair took 2.5 hours.  
     
  To A 9:  The last battery capacity test performed in Lorient showed an efficiency of 75%.  During this patrol, especially after failure of the distilling unit, due to abnormally heavy distilled water consumption by individual cells, serious troubles occurred.  
  Probably some cells have internal short-circuits, caused by lead mud, which – as well as sulfation – have significant impact on the output voltage.  These cells have to be renewed or desludged.  
  On 8 July, the battery was charged for 3.45 hours at 600 Ah, until generating oxygen and hydrogen. According to the machine log, there should be at least 10274 Ah available.  After withdrawal of 4944 Ah for driving motors, 2070 Ah for the boat's equipment and 165 Ah for losses, after 12 hours submerged cruise, there should be 3155 Ah remaining available.  
  At 23.10 hours, the main switch board voltmeter showed 109 V, which corresponded to about 1500 Ah while cruising at slow speed.   After reaching periscope depth at half speed with both motors at 23.13 hours, voltage decreased to 94 V immediately.  The diving planes driving motors stopped working at such a low voltage supply, and the diving planes remained in the following position: forward – hard up, aft – down 10°.  The broadcast and announcement system also failed.  The boat was not under control and had to be surfaced immediately.  
  Available Capacity:  7119 : 10274= 69%  
  Ratio to target capacity:   7119 : 12150 = 58% (50 hour-current)  
     
  To A 10:  Total operating time:  
                  Since last overhaul:  
                a) After disassembly of the internal exhaust gas valve, it was found that the seat of the valve was burnt or ground out over half of its perimeter.  Repair was not possible by on board means.  The external valve is tight.  
 

              b) On 13 May, the air compressor did not start.  The fuel pump plunger had been jammed during fuel priming.  Due to wear of the regulating spindle, it had canted when moving.  As a result a lateral force acted on the teeth of the pump plunger, which led to jamming of the plunger.  The regulating spindle was fixed by means of the guide screw and jamming was thereby prevented.  The shut-off gear on the safety valve was thus blocked.  The repair took 12 hours.

  
                c) On 25 April, the compressor had to be stopped, because of damage that occurred in stages 3 and 4.  After disassembly of the intake nozzles of the stage 4, iron shavings were found between the valve disc and valve seat, which caused pressure discharge from the stage 4 to stage 3. The origin of the iron shavings was not possible to determine.  Stages 3 and 4 were completely operable.  After a 20 minute test run, the same damage as described above occurred.  After multiple starts of the compressor, the stages 2, 3 and 4 did not receive starting air.  The compressor could not be started.  As a cause, it was determined that the ball of the check valve of the starting air line leading to stage 2 was jammed and prevented flow of the starting air.  The examination of the check valve showed, that the valve seat and fitting spring were damaged.  The failure in stages 3 and 4 is explained as follows: after failure of the fitting spring and the seat of the check valve of the starting air line for stages 2, 3 and 4, the valve's ball was swirled by the flowing compressed air (line illegible)  
     
     
     
 
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  compressed air through the compressor and caused the valve damage.  The repair took 15 hours.  
  The newly installed cooling water pump and automatic starting gear were running without any problems.  
     
  To A 11:  On 3 and 28 June, during crash dives, for an unknown reason, the port head valve was jammed about half way to “closed” position.  The valve must be disassembled in the shipyard.  
     
  To A 12:  a)  Due to contamination in the high pressure compressed air installation caused by iron shavings (see damage 10 c), the valve seats of the main blowing valve and regulating and negative buoyancy tanks blowing valves had to be overhauled multiple times.  
                b)  On 22 April in stage 3 of the electric compressor pressure increased abnormally.  In stage 2 pressure increased at a smaller rate, jammed inlet and delivery valves in stage 3 were replaced.  The repair took 1.5 hours.  
                c)  The loose clamping screws and scorched contacts of the relay in the diesel engine room engine order telegraph receiver caused momentary rattle in the starboard engine order telegraph in the electric motor room.   The repair took 4 hours.  
                d)  The hull valves of the blowing lines leading to tanks 7 starboard, 6 port and 4 starboard were improperly sealed with non-oil-tight material (hemp) and were leaking.  They were sealed with asbestos-graphite and since then they are tight.  
                e)  Despite especially frequent and thorough draining, 6 cartridge type, pressure reducing valves of type D 2500 (Dräger) were damaged by water hammer effect.  Evidently their construction is too sensitive for pressurized water.  
                f)  Despite appropriate rollers, the port shaft revolution transmitter failed because the drive chain slipped off even at normal bow down angles.  Damage is typical.  
                g)  Aerial bomb damage  
                     On 15 May, one aerial bomb, starboard abeam.  Damaged fuses and fuse sockets, as well as lamps.  Log indicator and depth meter in the conning tower are out of operation.  
  B.)         a)  Nothing of note.   
                b)  1:  Consumption of lubricating oil at a level of 3% shows, that newly installed piston and oil rings are correctly aligned. The heavy smoke of the starboard engine at end of the patrol was caused by flooding the cylinders with sea water two times.  Some of the failures described in paragraph A I should not have occurred after overhaul in the shipyard, which went on for 5 weeks.  
                     2:  Breakdown A 4  shows, that a second auxiliary drain and trim pump (piston type pump) would considerably increase the safety of the boat.  All previous patrols show, that in case of damage of the trim pump, draining of the bilges in the end compartments by the centrifugal pump is unreliable.  
                     3:  Breakdown 12 e  shows, that especially when the boat operates in the tropics, it seems advisable that sensitive low pressure regulators should not be connected to the lowest outlets of the high pressure air distributor to avoid carrying away accumulated water.  
                     4: Refueling of 43 m³ fuel oil from “U-459” was conducted quickly and without problems.  
     
     
     
 
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                     5:  With plugged drain connections in the diesel engine room, there is no possibility of draining the bilges with the trim pump by means of a flexible hose.  A moderate amount of necessary threaded fittings would increase the safety in case of a water leak.  
                     6:  The plexiglas water level gauge of the regulating tanks and the plexiglas tube for the Papenberg instrument, which were installed during last overhaul in the yard, did not break when the aerial bomb exploded quite near.  
     
 
 
Port Motor
Starboard Motor
               
 
Days
Hours
Min.
Days
Hours
Min.
 
Total operating time since commissioning:
220
18
33
221
15
30
 
Total operating time during the last patrol:
37
7
37
37
22
15
 
Revolutions since commissioning:
83
148
596
84
922
374
 
Revolutions during the last patrol:
13
398
180
14
144
920
 
  Reached diving depth:  A +60 meters.  
     
  B.)  Consumption:  
     
  Fuel measured run, see enclosure.  
     
  Commissioning of the boat 8.10.1940  
     
  Presented:                                                                   The Chief Engineer  
  signed in draft  G e l h a u s                                         signed in draft  B ö e r  
     
     
  Kaptlt. and Kommandant                                            Kaptlt. (Ing.)  
     
     
     
     
     
   
     
     
     
     
     
     
 
 
  Flotilla Remarks:  
     
  To A 1 a)  This damage was probably caused by broken seat rings, which in turn was caused by loose retaining brackets of the seats of the inlet valve.  
  1 b)  Cause of the water intake: rupture in the cooling flange of the turbo-blower, between the turbine and blower (2nd case in last half of year).  The repair was done by welding, the flange must be renewed.  
  1 c)  The loss remains unexplained; while refueling the internal fuel oil tank, its capacity was measured and it was stated, that it was completely filled.  
  1 d)  The shield of the neck journal bearing was not sealed properly.  
  1 e)  The cooling water safety valve which quite frequently causes a water leak in the diesel room bilge must be tested at regular intervals (about weekly).  Only in that way, can one prevent surprises.  
     
  To A 2 a)  An inspection of the switch remains indicates that sea water entered the limit switch, either through an improperly installed cover, or through a defective stuffing box.  
  2 b)  Defective radial shaft seal; isolated case.  
     
  To A 3)  In the case of mechanical damage to the vapor pump, attempts at repair are hopeless; in such a case, there is the possibility of running the distilling unit as an over-pressure unit, which should be considered on all boats.  
     
  To A 4)  The driving motor was not aligned with the pump, which led to the destruction of the flexible coupling.   The pump ran roughly and noisily.  Alignment is difficult to perform because there are no fitting bolts provided for the motor. The breaking of the condenser coil was probably connected with the vibration caused by rough running. When overhauling the pump in the yard, the ball ring of the ball bearing was discovered damaged; it remains unexplained, if it was damaged during assembly of the pump on board or earlier and sped up the destruction of the worm gear. - New worm gear.  
     
  To A 5)  After repair of the check valve and venting cock the pump operates without problems.  
     
  To A 6)  The corroding of the vent line of the tanks, just under the vent valves reappeared again!  It appears more frequently than expected, there is a need to install line with thicker walls.  
     
  To A 7)  To the longstanding request to make conning tower hatch bearing stronger and more stable, it is noted, that after installing double spring, hatch failures will be rare. - This boat will be first one on which the double spring will be installed.  
     
  To A 8)  Isolated case.
     
  To A 9)  The battery of the boat must be considered exhausted.  By forming up, especially in the forward battery, all cells, even those which by means of previous output voltage measurement were indicated as damaged, were charged to the same voltage.  Capacity, however, was low and its value (at 20 hour current) was: forward battery 64%, aft battery 61%.  By performing multiple charging and discharging cycles, it was determined, that an output voltage of 146 V could not be exceeded.  Up to that voltage, the temperatures were within moderate limits (30-35C), with additional charging at a voltage of 146 volts, the temperature rose in a short time until reaching a final value of 45C.  During the current war patrol – to avoid achieving this high temperature and resulting high water consumption - generally, charging up to generating oxygen and hydrogen was not performed.  The battery then had to be deeply discharged, to reform it again.  After this patrol, replacement of the battery (in connection with thorough overhaul) is scheduled.  
     
  To A 10 c)  An investigation to determine the cause is being conducted.