Tores mailbox VIIC and VIIC/41 operation and technical details

[Don Prince]

Hello Mr. Tore,


When docking and during maintenance - if the fuel oil transfer pump was used to drain the fuel storage tanks, and no diesel engines are running so this source of water cooling compensating water is not available. How would they get the fuel oil from the storage tanks. The transfer pump is trying to draw fuel oil from the top of the tanks, I don't see what pushes the oil up??? unless they use the Auxiliary water cooling pump to force water through the diesel engines and then on to the header tank....

this issue was discussed on page 75 of Skizzenbuch.

Regards,
Don_

[tore]

Don.
In the unlike event of a major docking/repair with full fuelbunker tanks, the easiest way to empty the  fueltanks would be to use the aux, coolingwater pump to pressureize the compensating system as indicated on the image below, prior to entering the drydock. If this is not done while afloat, you might use a hose suctionconnection on the aux coolingwaterpump to a watersupply (yellow). The last oportunity would be to use the aux. luboil pump hose connection via the manholes.
Tore

[Don Prince]

Hello Mr. Tore,


U-93 through U-97 had 2 e-compressors
U-98 and above had 1 e-compressor and 1-Junkers compressor


Did U-92 and below only have 1 e-compressor?


Regards,
Don_

[tore]

Don.
As you know the VIIC was a further developement of the VIIB, the last VIIB submarine was commissioned in 1941 I guess.  You had an overlapping periode when the VIIC was introduced in 1940. I assume the first VIICs had two E compressors as the VIIBs and when the Junker freepiston compressors were introduced, they had quite some trouble related to the exhaust backpressure resulting in various exhaust outlet alternatives. In the transition periode the  VIIC boats U 93 through U 97 were equipped with two e-compressors. The highest pennant no. of the VIIB class was U-102, but it is no relation with the German pennant no. and commission year.
Tore

[Don Prince]

Hello Mr. tore,


In 1943 the Germans moved the hand wheel for venting the bow buoyancy tank from the forward torpedo room to the forward control room pressure hull above the hatch on the starboard side.


This was a significant and intentional change... I assume that the Germans wanted to vent the bow buoyancy tank to decrease the diving time; especially on a U-boat with the wider Atlantic bow. They would not need to vent the bow buoyancy tank on a standard dive, but in an Alarm Dive it may be advantageous...


In order to keep the horizontal balance, then I assume they would vent the aft buoyancy tank as well. The bow buoyancy tank would not need to be blown when surfacing because of the bow angle and height and with the open slots at the bottom of the tank; it would naturally drain. The only issue would be blowing the aft/stern buoyancy tank in this scenario, and that should be a normal function for the aft torpedo room crewman who have to assure the aft buoyancy tank is blown before starting the Junkers air compressor...


Comments?

Where is the stern buoyancy tank blowing valve located it the aft torpedo room?

Regards,
Don_

[tore]

Don.
I guess the developement of the buoyancy tanks is a bit more complex and has to be seen in conjunction with the VIICs developement from the VIIBs. When the VIIC was designed they lengthened the pressurehull to be able to accommodate more equipment. At the same time they were able to introduce the Untertriebcelles (Q Tanks) in the saddletanks. At the time these changes were made a submarine was still a surfacevessel able to dive, rather than a true submarine, and as the radar was still not an instrument regulary in use surface cruising was done to and from the battlefield and an improved surface condition was neccesary. As a concequence of the improved surface behaviour, the buoyancy tanks were a problem as they increased the "surface resistance" when diving, which lead to filling the Q tanks while cruising on the surface to overcome the surface resistance in the event of crashdiving. In case of bad wheather, this would make life hard for the people on the bridge and empty buoyancy tank as well as a later introduced Atlantic bow  would improve the matter. It is important to emphasize that the buoyancy tanks are not ballast tanks but merely tanks for surface improvements and do not take part in the diving/ surfacing procedure thus the are to be considered as free flood areas when diving.
I agree with your conclusion on the blowing of the buoyancytanks as well as the aft buoyancytank blowing when operating the Junker compressor. As you know an interlock was installed in the Junker exhaustsystem preventing to open the exhaustvalve unless the vent for the aft buoyancy tank was shut.
Tore

[Don Prince]

Hello Mr. Tore,


I don't believe there is any need to blow the stern buoyancy tank if they vented the Atlantic Bow buoyancy tank because the buoyancy tank's effect on the longitudinal balance becomes insignificant with depth.


Bow Buoyancy Tank Vol (m3) - Versus Depth (m)       Stern/aft Buoyancy Tank Vol (m3) – Versus Depth (m)
                 8                                  sea level                                       4.28                               sea level
                 1.34                             50                                                 0.72                               50
                 0.73                             100                                               0.39                               100
 
At 100 meters depth, the volume of the air in the aft buoyancy tank is 0.39 m3 and this calculation has not considered the volume change due to cooler water temperature with depth (reduces the volume again)!


What do you think?


Regards,
Don_

[tore]

Don.
As I said before the buoyancy tanks are not ballasttanks and do not participate in the diving and surfacing procedure, when  diving and surfacing the vents are open and the tanks are to be considered as freeflood areas. Surfaced they are elements in reducing the pitching of the submarine by shutting the vents.
Tore

[Don Prince]

Hello Mr. Tore,


Do you or Maciek know which valve in the aft torpedo room is used for blowing the aft buoyancy tank?


Also, what is this hand-wheel for in the attached photo in the red circle?


Regards,
Don_

[Don Prince]

Hello Mr. Tore,


On page 420 in Skizzenbuch you are talking about a uhistoria.com image...  Where is this image?


"The linkage consists of a bell crank lever which snaps the cones in a locked in position. On the u-historia.com photo you see the worm rod and the piston rod fixed to a yoke having two guide rods. At the ends of the guide rods are some peculiar "nuts." These are spring loaded end stoppers; when the linkage snaps into position they push the actuating lever a fraction back to release the engagement at the shaft slide to prevent a possible hot running."


Regards,
Don_

[tore]

Don.
The U historia images are found on the U historia homepage, look to Visita Guida then Sistema Embrague which is the mainengine clutch. Since I wrote my comments on the clutches I got hold of Falos photos which are at least as good if not better. A small correction could be nessecary with regards to the hand operation of the clutch. I introduced a key and a sliding slot, as Falos images are better I discovered a locking bolt which might be used to fix the travelleing nut to the yoke assembly in case of handwheel operation.
Tore

[tore]

Don
Blowing of buoyancy tanks. I cannot find the LP air valve to the stern buoyancy tank. The buoyancytanks were not connected to the tankblowing system, but had a branch off from the ordinary LP system, like weedblowing and mainengine clutches, if you have images showing the LP pipes from the aft engine room it might be possible to trace the valve for the stern buoyancy tank. The handwheel in the red circle I cannot identify, may be Maciek has a clue.
Tore

[VIC20]

Tore, what means LP?

[SnakeDoc]

Tore, what means LP?

I will answer this question: LP means low pressure air.


--
Regards
Maciek

[VIC20]

Thanks.