Tores mailbox VIIC and VIIC/41 operation and technical details

[tore]

Ejector drainer VIIC.
I believe the ejector drainer is built upon a well known principle and used in naval engineering. The system was frequent used during WW2 as damage control pumping where steam ejector pumps could handle large quantity of water. In order to try to explain the reason for the position of the ejector drain ( and flood gate) I made the image below showing the horizontal crosssection of a VIIC about the level between the upper and lower torpedotubes. The pink colour indicates the MBT 5 and the blue the difficult and narrow void space between the casing and the pressurehull. When the submarine speeds ahead there shall be a suctioneffect in the "nozzle blister" draining the void difficult space. The ejectorblistesr seems to be located at the same draftlevel as the floodgates for the bow buoyancy tank. For a submarine not having a double hull I guess the VIIC has fewer flood gates than the conventional submarines of other navies  during WW2. I am posting an image of a RN WW2 S class (having 6 torpedotubes and not double hull) being only slightly smaller than VIIC,  showing the floodgates.


Tore

[Don Prince]

Hello Mr. Tore and Maciek,


Great job Mr. Tore!  I updated Skizzenbuch on page 85 with the "Blister" information and added 2 pages to the torpedo section.  Just a little info on charging the batteries in the G7e torpedo with photos provided by Maciek.  I uploaded the latest version of Skizzenbuch into Dropbox...


Regards,
Don_

[tore]

Uboatfan.
You shall find the relevant drawings on the pages of U-Historia. Tecnica, Visita Guida, Construccion. You`ll find the link in the last post from Maciek.
Tore

[tore]

Don.
I checked your to days Skizzenbuch page 85 and have following minor remarks. I don`t think you are meaning the Uboats were cursing on the surface . May be you should add that the drain ejectors are situated at about the same draftlevel as the bow buoyancy floodgates. As an example of floodgates on other navies WW2 subs floodgates in the area I posted a photo of me diving in the oldfashioned WW2 equipment near the bow of a RN T class WW2 sub. clearly illustrating the ample floodgates in the area.
Tore 

[uboatfan]

Hello,

Tore explained exactly what i mean. Great job. Thank you. Al the jears i thougt about this blisters an their real funktion. Now the riddle is solved...

I always read about a Skizzenbuch.
Where can i find this?

Regards,

Uboatfan

[tore]

The Skizzenbuch is in currently made by Don Prince who seeks advises on this tread. I don`t think the book is completed as yet and I don`t know what Dons final intentions are, but in the last year it has increased in volume and is right now a book of 432 pages on the VIIC. Don is one of the VIIC enthusiasts who collects all sorts of info on the matter as you can see on this thread. I am merely a consultant being a very old submariner and ex. EO of KNM Kaura ex U 995 and KNM Kya ex U 926 in the 50 ties.
Tore

[Don Prince]

Hello Mr. Tore,


Very interesting...  So you served on U-995 VIIC/41 and U-926 VIIC; I believe U-926 was scrapped in 1962.  Did you serve an any of the later subs like the Ula Class jointly developed by Norway and Germany (U-Boot Klasse 210 - Diesel-electric)?  Others?

PS: Yes I can see where the blisters align with the flood gates.  If the U-Boat is submerged, then the entire bow free flood area would be flooded.  The blisters would allow a small amount of water to flow through the bow free flood area, but that wouldn't affect the drive performance. Would it?


When running on the surface, water from the flood gate will flow up over the rounded bow pressure hull approaching the level of the lower set of limber holes in the U-Boat outer side casing.  I thought the function of the blisters was to evacuate the water.  If water was allowed to pool in this area, then it would result in a slight increase in bow weight.  At that distance from the center of gravity it only takes a little weight to lower the bow, and with a lower bow the U-Boat will require more power to maintain a set speed.


Of Course, I could be off on a tangent again... Please advise!

Note* The photo you posted of U-995 demonstrating the alignment of the flood gate and the blisters, the U-Boat looks to be running very high in the water.  The flood gate and the upper torpedo tubes look to be out of the water (the waterline is way above the surface).  Is this an unusual running condition?Regards,
Don_

[tore]

Don.
I am an old submarinefart who never served on any of the submarines built after WW2. The Ula class building programme was under the supervising of my CO on KNM Kaura (ex U 995) as well as KNM Kya ( ex U 926 )and we both served together these submarines when they were  operated as frontline subs.
I believe you are basically right in your assumption . However the blister ejector effect is depending upon the forward speed, in addition you have the buoyancy tank and later the Atlantic bow with the flare effect, all contributing to lift the bow pitching in bad weather.
We have almost exclusively been discussing the draining of the void spaces, but an other important detail is to flood the void spaces in a way that no air is trapped in the difficult areas.The blistergates would improve the flooding of the difficult void spaces as well preventing a treacherous track of airbubbles.

The photo showing the uboat bow buoyancy floodgates and the blisters  is in an extreme shallow draft condition I should think the boat is possibly without batteries, normally the buoyancy tank floodgates and the blister is just below the waterline.
Tore

[Don Prince]

Hello Mr. Tore,


I have uploaded the latest version of Skizzenbuch to dropbox.  This version contains the corrected info per Maciek with regards to the Switchboards and updated info to the two Switchboad panels; Rotary and Toggle blade.  I found this issue when reviewing the panel drawings from the U-boot Museum schematic documentation (i.e., the accelerating contactor).  I also removed the extensive word capitalization in the text on my part; that was to make it easy for me to identify what was being covered on a page.


If you see any problems, then please advise.  Maciek will be back next week and he can verify the switchboard identification info to see if I finally got it right!  I was really struggling with the concept... 


This has been a long educational process for me and I really appreciate your and Maciek's help along the way.  After I get your and Maciek's approval, then I will commit the Skizzenbuch.pdf to a printed copy for my Leather covered post binder.  That was my original goal when I started my Skizzenbuch project; to have a book that explains how a Type VIIC U-Boat actually worked.


I have 3 different publishing companies who have downloaded the final version and it may actually become a real book.  However, I am not optimistic about this prospect because I would be an unknown author, but there is nothing like Skizzenbuck offered to the public or a U-Boat enthusiast.  So. we'll see...


One additional benefit is that I have two great friends who are experts on U-Boats!  Perhaps, I may consider another Skizzenbuch based on the Type IX U-Boat.  However, I need a break for awhile before I consider another project.   


Kind regards,
Don_ 

[tore]

Don.
Having a brief check on your final Skizzenbuch I discovered a small mistake on the crossection drawing of the Junker compressor, the 1. stage compressor inlet chamber is not marked properly, only the scavenging air inlet. As this might be confusing for the reader who wants to go into details I recommend to correct this. The compressor atmospheric air inlet is via a common airfilter as indicated, however it is branched off in two inlet , one for the diesel part and one for the first stage compressor part. I have updated the drawings on page 90 and 95 accordingly as per my images below.
Tore

[Don Prince]

Hello Mr. Tore,


Thank you for the updated info...



On Page 95, I cut the old drawing and pasted the new Junkers exhaust.jpg in; not a problem...


On Page 90 I copied the changes over from Junkers exhaust b.jpg onto the existing drawing because I liked showing the cylinders and the bouncing chambers in two different positions.  If I just added the Junkers exhaust b.jpg to Skizzenbuch as another page, then I would have to add a 2nd page to sync up the rest of the book because the schematic Plates need to be on a odd page number; re-do the page numbers and the index... I would like to avoid that if at all possible.


Please let me know if what I have done meets with your approval?


Kind regards,
Don_

[tore]

Don.
Your copies are OK. Note the crossection drawing is of a Japanese  Junker made under license by Kohama and used for Japanese submarines during WW2, however they are basically the same.   One thing strikes me though, the opposed pistons on the Junker compressor have deep recesses located near the piston crowns which can be confusing on the drawing with regards to the scavenging chamber.  These recesses are simply access recesses to the fixingnuts for the pistoncrowns and have as such nothing to do with the scavenging chamber, see my sketch below.
Tore

[Don Prince]

Hello Mr. Tore,


The is interesting, as to how the piston crown was attached to the Compressor 1st and 2nd stage.  I don't believe I want to go that deep into the Junkers compressor in Skizzenbuch.  However, for my own knowledge this access looks like a means to disconnect the piston crown from the compressor's first two stages.  The piston crown burning and carbon deposits were a maintenance issue.  Just how far did the mechanic have to go in tearing down the Junkers compressor to remove and clean or replace the piston crowns?


Regards,
Don_

[Don Prince]

Hello Mr. Tore,


One more question about the Junkers Compressor...  Did it have a piston sleeve to protect from wearing out the compressor casting?



That brings up an off-topic interesting question...  Junkers licensed Kohama to build the U-Boat compressor; were companies bound by International Law to respect the copyright laws even though the countries were at war?  Could the U.S. Department of Defense tell General Electric to build the compressor for American submarines; besides the Russians had stolen the Atom Bomb secrets from the U.S.?


Regards,
Don_

[tore]

Don.
I believe Kohama was a Japanese professor involved in the technique and that the licence was sold by Junkers to Kobe steel as an ordinary business agreement before the war.
Tore