Tores mailbox VIIC and VIIC/41 operation and technical details

[tore]

Katuna.
Yes you found the the main dieselair inletvalve and the rectangular duct to each of the engines. I don`t think the downfolded topplate for the mainengine bedplate plays a role in the dieselair ducts, they are mainly a strenghtening element in the engine foundation. Apart from delivering air to the engines the ducts are draining the seawater freely to the bilges. As to the diesel air shaft going from the main inletvalve in the towercasing to the main hullvalve at the engineroom it add a fairly large enclosed airvolume to displacement when submerged. We once had an unpleasant issue after a refit during some testdives in a deep fjord. Somehow the dieselair mainvalve in the tower didn`t shut properly and the diesel air shaft gradually got filled with seawater. We just dropped down like an elevator and at some 50 meter we blew all the ballast tanks and everybody were staring at the depthgauge  which just kept moving until it slowed down and finally the needle pointed at some 125meter before the submarine stopped and very slowly started to ascend. Then she accelerated towards the surface as the air in the ballasttanks expanded and the  ex U 995 broke the surface like a spectacular rocket, a highly irregular (and dangerous) surfacing. She had some damages in MBT 3 and we had not had a deep testdive since then, which caused some excitement.
Tore

[Katuna]

Wow! That is the kind of experience that makes for a great story after the fact but not at the time. Just like out of a Hollywood movie. Not a pleasant experience at the time I'm sure. Thank you for sharing that with us.


Do those ducts just curve downward between the frames and then abruptly end at a certain point? I see now in some of the drawings and some photos of U-995 how the duct goes across the top and turns downwards but you cannot tell how or where it ends.

[Don Prince]

Hello Mr. Tore,


I remember where U-926 had some MBT3 damage issues and that was the reason she was left for the Norwegians because she was deemed unfit for sea duty. Could that have been the cause of the MBT3 damage to U-926 where the diesel air main external valve under the tower failed to shut? Otherwise, I believe they could have sabotaged U-926 by blowing MBT3 and running at depth with the dive planes down until the Kingstons were shut, and then rising. That would damage MBT3 and make U-926 unfit for the enemy to use after the war ended...

I know, I have a devious mind...

Regards,
Don_

[tore]

Don.
You are correct in you memory about U-926 avoiding operation searchlight. I guess the investigation revealed that possibly the germans had blown MBT with shut Kingstons. At the end of the war it was difficult to get skilled submarine crew and opening and shutting of the Kingstons was not a daily event as you had to use special cranks. It could have happen by accident during moving the submarine. If I remember correctly the testpressure of MBT 3 was only 30 m H2O. I have also heard that she probably had open Kingstons during an allied air attack on the submarine pen in Bergen. Anyhow she did a firstclass service as a NATO submarine in the 50ties.

Tore

[tore]

Katuna.
I guess the tapered steelplate lips for the engine bedplate ends towards the frames where they are fixed by welding.
Tore

[tore]

To all your guys following my thread, I shall leave for my farm in remote wilderness with bad internet connections hence my activity shall be reduced for a couple of days. Back on monday.
Tore

[Don Prince]

Hello Mr. Tore,


Be very careful with the drive to the farm... NO repeats of last year!


I have remarked the drawing... Does it look OK.


Regards,
Don_

[tore]

Don.
My son in law is driving hopefully we arrive safely and no repeat of last year. I shall revert with further comments over the week end. Is Simon around or is he still chasing the snow?, I guess he did a lot of research before making the drawing. Back on monday.
Tore

[Don Prince]

Hello Mr. Tore and Katuna,


It's Winter season down under in New Zealand, so I guess Simon is busy at work studying avalanches and working on his advanced degree!


Good discussion... This subject was not covered before in such great detail. It looks like the air induction box is extended on both sides with sheet metal plating and screwed to frames 25 and 26 (My best guess). That way in rough seas where water enters the diesel air intake stack below the bridge, it will be dumped into the Bilge to the drain structures previously discussed.


I believe the Diesel engine running aspirated or supercharged will draw the air from the air induction plenum. Does this sound about right?


Drawings attached,


Regards,
Don_   

[Don Prince]

Hello Mr. Tore,


Looking at one of Simon's drawings makes the drainage and engine block support look entirely different. The lighter structure seems to attach to the frames and the engine block to form the support for the Diesel engine room.  Also, I believe the dark area between the frames to the right is indicating the frames where the air induction plenum is located above. What do you think?


Regards,
Don_

[tore]

Don.


I guess it would make it easier not to combine the bedplate structure and the diesel airshaft, they really don`t relate to each other as the diesel  air shaft ends far away from the diesel engine air intakes. The combustion air of the diesel is either normal aspirated or supercharged. When the engine is in normal aspirated air mode, air is drawn in via a rotary inletvalve into an airmanifold alongside the engine, from this manifold are separate ducts to the inletvalves on each cylinderhead. When the engines are running supercharged you clutch in the Roots blower, at the same time you rotates shut the aspirated air manifold inlet valves, as the roots blower discharge is directly connected to the aspirated air inlet manifold, the manifold is now becoming supercharged airmanifold.  As all the air inlets are far away from the outlet of the dieselair shaft the drain of the shaft do not interfere.
Tore

[tore]

Don

The topplate for the mainengine bedplate is a very thick steelplate on which the main engine bedplate is bolted and adjusted by shims. The plate is drawn on the image below and outside the landing area of the engine bedplate, bent down and welded to the pressurehullstructure (frames) for a very rigid connection to the pressurehull. The ligth blue-greenish coloured area are open surfaces and the light grey area the topplate extended down to the pressurehull frames.
Tore

[Don Prince]

Hello Mr. Tore and all,


I updated Skizzenbuch pages 239 (images), 240 (text and images), 350 (image) and 351 (images). I placed the latest version of Skizzenbuch in Dropbox...


Regards,
Don_

[Katuna]

Tore - I noticed these baskets in the Engine Room and another in the Control Room. Were these original to the boat or added post-war?

[tore]

Katuna.
These were indeed "baskets" for storage which we used for spares and tools. I guess during the WW2 they were used for, provisions as well it was seldom needed  for foodstorage in my time.
Tore