Tores mailbox VIIC and VIIC/41 operation and technical details

[Don Prince]

Hello Mr. Tore,

In order to eliminate any possibility of confusing the reader of Skizzenbuch, I took your suggestion and updated pages 38 through 46.  I uploaded the latest version of Skizzenbuch to dropbox.

Please advise if I got anything backwards, or used the wrong context...

Regards,
Don_

[tore]

Don.
You update seems OK. to me, just a small misprint i qouting my remarks on page 38..... " as soon as the U-boat is submerged at normal trim, speed and the hydroplanes control the decent effectively.... I wrote descent but I hope the control goes decent as well .
Tore

[Don Prince]

Hello Mr. Tore,

Just for my own info....

I have a question about the regulating tanks set-up as a shallow dive tank.  When you want to decrease the contents of the tank, in this case you use air pressure to discharge some water into the sea, or MBT 3. Do you bypass the Main bilge pump with the two valve chests, or do you use the pump?

Regards,
Don_

[Don Prince]

Hello Mr. Tore,

I corrected the spelling of "descent" on page 38, and added some context to page 47.  I uploaded the latest version of Skizzenbuch to Dropbox...

Regards,
Don_

[tore]

Don.
You  normally don`t discharge the water by air through the main bilgepump pump.  In this case I guess I would discharge to the main valvechest and to the sea valve ,
However if the relevant tank is the reg and fueloil tank no 1 recently used as fueltank I would discharge into MBT 3. Just to give an indication of the many aspects and alternatives you have, I guess there is no single right answer for all conditions. You can compare a VIIC with an instrument well designed and the men that plays her as musicians. There are many ways to get the best out of her, depending upon the skill of the players, a manual cannot cope with all the variables and as such tell you what to do. The standard of the boat is set by the knowledge, skill and experience of the crew.
Tore

[tore]

Transferring liquids in a confined space is in some cases difficult to understand.
May be the trim system used for compensating for weight shifting fore and aft gives an explanation.
The image of the system is shown below. One trimtank is situated forward and one aft, an approximate distance between the tanks of some 41,6 meters gives a proper correctional momentum by shifting a relatively small amount of water in the system. The water can be transferred either by the trimpump or airpressure. When the system is operated by the trimpump, water is pumped through the trimline. The volume of the shifting air and water in the confined system is constant (you don`t add air or water to the  system) and according to plate 6 you don`t have local venting, everything is centralized in the controlroom. However as the volume of  water is shifted, the air volum ("venting") has to be shifted as well. This can be done by the airpipe between the tanks by putting the blow/ venting cock in the pumping position, straight through the cock as indicated on my image below, allowing the air to move between the tanks. Thus by pumping water from one tank to the other the ventingair can be shifted to the opposite tank via the airpipe. 
   When  trimming by airpressure the valves to and from the trimpump are shut, the water distributing ( Schalter) valve is put in a middle position and you have a direct water connection  between the two tanks, shortcutting the trimpump. When selecting the tank for air pressurizing (blowing) you put the air / venting cock in the airpipe in the required position and as you pressurize one tank by the air blow valve,  you vent the other. As you admit air to the system the tanks have to be vented into the boat, which means increasing the inside pressure of the pressure hull.
We usually used the trimpump avoiding increasing the ambient air pressure in the boat.
 The above is just an example to illustrate the physics of moving liquids and air in a confined space like a submarine.


Tore

[Don Prince]

Hello Mr. Tore,

I added some info to the compensation section and uploaded the latest version of Skizzenbuch to dropbox.

Regards,
Don_

[tore]

Don.
I think you put the description of the two ways of trimming just on the right place.
 When you see the VIIC system like the trim arrangement photo in the controlroom, having all the rough essentials in one place for trimming, it strikes me we did not badder to have a special place for the trimoperator who should handle the system. In to days submarines I guess the same system is installed, however the operator is probably sitting in a proper designed chair, looking at a screen, pushing coloured buttons for the same functions (and even more) as we turned the valves and cocks standing, stretching and twisting around using our ears, noses and eyes to monitor the operation. It calls for some reflections, today you put in  extra technical elements between the human operator and the piece of equipment we are controlling, are we loosing our the ability to use our senses by introducing  extra elements which might have a potential of failures? The VIICs are one of the last advanced mechanical, directly controlled submarines which made it unique though cumbersome to operate and maintain, thus having the disadvantage of requiring a large crew. To days submarines of the same size would probably have a crew of less than half of the VIICs and still a larger striking power.
Tore

[tore]

Don.
Referring to page 78 having showing an image of the fueloil watercompensating system plate 10 you have a description of same underneath starting with "when the U- Boat submerges.... I believe your explanation is a bit unclear and would suggest a text some thing like this : When the U-boat submerges the header tank systempressure is kept constant, equal to a liquid column height from the compensating pipes sea inlet in the external fueltanks and the top of the header tank waterlevel, regardless the divingdepth of the U-Boat. The internal fuel tanks are shut to the external compensating system by the hull valves "a" on plate 10. 
Tore

[SnakeDoc]

Hi Tore,

while cruising submerged (using electric motors), did you shut the internal fuel tanks to the external compensating system? I mean, if it was common practise to isolate them from the external pressure?

In the KTB from the 2nd war patrol of U663 there are described some damages:

Schaden: 25 cm langer Riβ in TZ 3 durch Sull Mannloch, Riβstelle nach innen gedruckt. TB 1 und 2 innen ständig unter Druck. Wassereinbruch 8 t in 3 Std. im Dieselraum aus Entwässerungsschalter.

My translation:

Damages: The coaming of the manhole of the main ballast tank 3 torn. The edges are bent inside. Internal fuel oil tanks 1 and 2 remain under (external?) pressure. Water intake 8 tons per 3 hours in diesel engine room through the bilge/drain system.

From the description I suppose, that internal fuel oil tanks are somehow no more pressure resistant. And thus my initial question...

And by the way - what do you think about this torn of the coaming? As far as I know, the only manholes of the main ballast tank 3 are located in the control room, so I wonder, how they could damaged (and if the coaming is needed at all inside the boat)?

--
Thanks, regards
Maciek

[tore]

Maciek.
As a rule we shut all the boardvalves not needed when diving and for sure the compensating water to the inboard fueltanks.
With regard to the manhole and damage on MBT 3 I wander what caused the damage, was it by blowing the tank? or was it depthcharging or deepdiving. As adviced previously U 926 got a damage on MBT 3 by blowing.
MBT 3 has separate Kingstons and blowing and venting valves for starboard and port side. On several drawings the tank is drawn and  marked as MBT 3 port and stb. Between the port and starboard side of the tank there is a center bulkhead, I believe not pressureproof, you can see this on several drawings and on U-historia images the bulkhead is used for supporting the bearings for the  operating rods for the Kingstons on both sides. In this bulkhead you have a manhole see my image below, I should not expect a coaming on this cover. I guess you can easily damage this bulkhead if the differential pressure between the two sides become to large, but I am at a loss to explain how they could observe the damage . This is just a far fetched idea and bad assumption from my side." TB 1 und 2 staendig unter druck" does not give much meaning to me. The tanks have reliefvalves both for pressure and under pressure, moreover you could shut the hullvalve and relieve the pressure in to the wastetank or other inside tanks.

[Don Prince]

Hello Mr. Tore and Maciek,

It looks like all the damages to MBT 3 were the results of a depth charge attack from a destroyer on the 13th and 14th of December 42 during their 1st war patrol.  Overall, U-663 was just too close to the pounding of depth charges for 2 days.  MBT 1 and MBT 5 have comb type grilling over the vents on the top side.  I could see them getting pushed inward from depth charge explosion pressure...

U-663 History
1st patrol 5.11.42 left Bergen returned Brest - Damaged 31.12.42 (repairs took about 2 months)
                4.3.43 left Brest returned 6.3.43
2nd patrol 10.3.43 left Brest returned Brest 4.4.43 - no damage reports
3rd patrol 5.5.43 left Brest - 7.5.43 attacked by aircraft Sunderland (RAAF) declared lost 8.5.43 - no survivors.

The very short life span of U-663.

Regards,
Don_

[Don Prince]

Hello Mr. Tore,

I changed page 78 as suggested and uploaded the latest version of Skizzenbuch to dropbox...

Regards,
Don_

[tore]

Maciek.
The report of U 663 says "Wassereinbruch 8 t in 3 Std im dieselraum aus entwaesserungs schalter." I guess in case of depthcharging, without shutting the board valve exposing the internal compensating system for excessive pressure fluctuation like a depthcharging, the two cocks marked on the drawing might burst and you get a substantial  waterflow into the engine room via the broken entwaesserungs schalter. It t. However you could avoid exposing the internal fueltanks for same pressure fluctuations even with open hull valve by shutting the valves "c" to the tank 1 and 2. It looks indeed like they did not shut the hullvalve, neither did they shut the c valves when the increased internal pressure occurred which could be a fatal mistake.
Tore

[SnakeDoc]

Hi Gentlemen,

Tore, thank you for your answer.

With regard to the manhole and damage on MBT 3 I wander what caused the damage, was it by blowing the tank? or was it depthcharging or deepdiving.

The damages were caused by depth charging. While pursuing SC-123 convoy, she was spotted by HMS Vanessa (D29) and forced to dive. During the first (of four) attack, destroyer dropped eight well-aimed depth-charges.

TB 1 und 2 staendig unter druck" does not give much meaning to me. The tanks have reliefvalves both for pressure and under pressure, moreover you could shut the hullvalve and relieve the pressure in to the wastetank or other inside tanks.

I suspected, that somehow the tanks themselves or the compensating installation was not tight and exposed to the external sea pressure.

The report of U 663 says "Wassereinbruch 8 t in 3 Std im dieselraum aus entwaesserungs schalter." I guess in case of depthcharging, without shutting the board valve exposing the internal compensating system for excessive pressure fluctuation like a depthcharging, the two cocks marked on the drawing might burst and you get a substantial  waterflow into the engine room via the broken entwaesserungs schalter. It t. However you could avoid exposing the internal fueltanks for same pressure fluctuations even with open hull valve by shutting the valves "c" to the tank 1 and 2. It looks indeed like they did not shut the hullvalve, neither did they shut the c valves when the increased internal pressure occurred which could be a fatal mistake.

It makes sense to me.

--
Thanks, regards
Maciek