Tores mailbox VIIC and VIIC/41 operation and technical details

[Don Prince]

Hello Mr. Tore,


I believe I got everything corrected in Skizzenbuch in the Junkers section.  It sure is hard to distinguish the green text, but I think I got it right...  I uploaded the latest version of Skizzenbuch to dropbox for your review.  Thanks again for the corrections, and that's not a problem for me to make corrections because I want to get it right.


Kind regards,
Don_

[tore]

Don.
I had a look through the Junker part of the Skizzenbuch 13 and may be we are going into too many details as it is always something which has to be adjusted or corrected. On page 90 first paragraph of the description the correct text should be... The dieselpistons are directly connected to the first and fourth stage compressorpiston at the scavenging ports side.....
Page 91 starting procedure.... Approximately (appr)..somehow you got bold letters on several places.
             3 rd lowest line ... first-  should be f. inst.
Page 93 drawing of the bouncing chamber. The arrangement of the first stage compressor cylinder scavenging air outlet ports. On the crossection drawing you see on one side the port, on the other side is a chamber wrongly coloured green. This is in fact a channel belt covering the ports going around the cylinder and should be coloured the same way as the scavenging air box.
In addition the image of the first 1/3 of the first stage compressor stroke shows wrongly a green stripe ( scavenging air) right thru the piston assembly
If you use the two images below as a substitute for the two in your book you should be OK.
Tore

[Don Prince]

Hello Mr. Tore,


what is "f. inst" abbreviation stand for?


Regards,
Don_

[tore]

Don
For instant.
Tore

[Don Prince]

Hello Mr. Tore,


I changed over the two images and I believe I have made all the suggested changes,,.  I uploaded the latest version of Skizzenbuch into dropbox.


Regards,
Don_

[tore]

Don.
I checked the last changes in your Skizzenbuch and it seems OK.
Tore

[Don Prince]

Hello Mr. Tore and Maciek,


My write-up on the torpedo section states the torpedo tubes were vented into the pressure hull when the torpedo launch piston was pushed back by the sea water during a submerged launch.  However, a colleague of mine indicates the blisters on the front side of the hull were vents for the torpedo tubes. 


My question:  Did the early type VII U-Boats vent the torpedo tubes externally?  If so, did this not defeat the purpose of the piston to eliminate air from escaping and expose the U-Boat's location after a torpedo launch?


See Photo...


Regards,
Don_

[tore]

Don.
As you know I am not a torpedoman and Maciek is much better in giving you an explanation of the system. All our VII Cs had these "blisters".  I post some images showing KNM Kaura ex. U 995 in drydock in 1954 being a VIIC/41 ( 1943) Appart from the conningtower pretty much as the original shape. Further in her 1962 shape and lifted by a crane in Kiel approximately 1970 as delivered from Norway. Finally as museum boat at Laboe 1972. You clearly see the "blisters) on the two first images whereas they are removed on the museum boat.
In 1953 we tested a surface torpedolaunch ( with a dummy torpedo) just outside the submarine pen in Trondheim I took a picture of the event as posted.
Tore

[uboatfan]

Hello togehter,

some years ago they was another discussion about these marks on the hull: http://models.rokket.biz/index.php?topic=221.0

From my point of view these marks are not related to the torpedo system.

These "bumps" have a very simple work to do: They helps to get out the huge amount of water inside the free flooded structure.
This water at this position was a big problem out at sea. Water at this position results to a hard working boat.
This problem occurs first at Type I. Later also on Type VII A. They try to fix it by many different changes of the first flooding holes. At some pictures of U35 you can see that they have also opend additional flood holes just at the position of the "bums" of later Types. This helps to get out the water. But also the water could fast get in.
At development of type VII B they ad these "bumps". This are just open flood holes. But at speed foreward the water could easy get out but nothing or only slow get in.
If someone owns a smal boat he maybe used a very similar thing to get out the water. In german it calls "Selbstlenzer".

Regards,

Uboatfan

[SnakeDoc]

Hi Don,

My write-up on the torpedo section states the torpedo tubes were vented into the pressure hull when the torpedo launch piston was pushed back by the sea water during a submerged launch.  However, a colleague of mine indicates the blisters on the front side of the hull were vents for the torpedo tubes. 


My question:  Did the early type VII U-Boats vent the torpedo tubes externally?  If so, did this not defeat the purpose of the piston to eliminate air from escaping and expose the U-Boat's location after a torpedo launch?

I also think, that these blisters are not related with the torpedo tubes (or venting the tubes).
On the u-historia.com site (unfortunately it is not working now) some time ago they published description, that this blisters were responsible for releasing the pressure inside the tube (caused by forward movement of the boat), when the muzzle doors were opened. This higher pressure had to influence for the depth-keeping apparatus of the torpedoes.

This blisters seems to be located near the breech doors of the tubes. However, when I was visiting U995 museum, I was looking for any connections passing the pressure hull in this area. I have found nothing.

So I guess that description is quite accurate:

These "bumps" have a very simple work to do: They helps to get out the huge amount of water inside the free flooded structure.
This water at this position was a big problem out at sea. Water at this position results to a hard working boat.
This problem occurs first at Type I. Later also on Type VII A. They try to fix it by many different changes of the first flooding holes. At some pictures of U35 you can see that they have also opend additional flood holes just at the position of the "bums" of later Types. This helps to get out the water. But also the water could fast get in.
At development of type VII B they ad these "bumps". This are just open flood holes. But at speed foreward the water could easy get out but nothing or only slow get in.
If someone owns a smal boat he maybe used a very similar thing to get out the water. In german it calls "Selbstlenzer".

--
Thanks, regards
Maciek

[tore]

I am fully in agreement with Maciek and uboatfan, I can not find any system sketches showing pressurehull passages related to the "blisters" for the torpedo systems. I believe there are some void spaces in the joint between the casing and pressurehull difficult to drain/vent. The "blisters" would possibly be ejectors drainers creating a suction as the boat moves forward and improve the flooding while diving. I never pounded upon these " blisters" but have seen many  people discussing same as a torpedo venting device. Allthough not very involved in the the torpedo system,I remember while launching the torpedoes submerged we always felt it on the ears due to inboard venting.  On the image below I have tried to show the system by superimposing  a couple of sketches.
Tore

[SnakeDoc]

Hi Gentlemen,

On the u-historia.com site (unfortunately it is not working now) some time ago they published description, that this blisters were responsible for releasing the pressure inside the tube (caused by forward movement of the boat), when the muzzle doors were opened. This higher pressure had to influence for the depth-keeping apparatus of the torpedoes.

The u-historia.com website is online, the problems with the connections are on my side.
Anyway, the description I was talking about can be found here:
http://u-historia.com/uhistoria/tecnico/visitaguiada/tlt/tlt.htm
in the paragraph labelled as "Comunication exterior".

However, as I said before, I do not agree with it. One drawing presents the hull valve located in the forward torpedo room, at port side, near the breech doors of the torpedo tubes. It is valve used to flood the compensating tanks and to equalize the pressure in the torpedo tubes before opening the muzzle doors. It was discussed on this forum in this topic:
http://models.rokket.biz/index.php?topic=877.msg12687#msg12687
The image below, at left presents the equalizing valves, which are described here:
http://www.ubootwaffe.pl/en/u-boats/equipment/torpedo-tubes-of-german-u-boats
(paragraph "2. Torpedo tube flooding and drainage installation")

I can not say nothing about the valve on the right drawing.

--
Regards
Maciek

[uboatfan]

Hello together,

The picture at U-historia about the valve is completly wrong! If that valve is only located on port side why all boats have these blisters, bumps or markings on both side?
The real hull opening for this valve is visible just near to that. I have made a modification to a similar picture to show what i mean.
Second question is wy did only type VII subs have these blisters, bumps or markings?
If they are related to the torpedo system in any way: Show me equivalent openings at aft torpedo tubes or at any other german sub! You will never find something...

So (after thinking a long time about this issue) the only logical solution is that these things are a special solution only for Type VII subs.

And finaly you will find at many other geman subs very similar solutions for the same problem.
By the way: Some type IX subs have very similar bumps at front and rear!

A question to Tore:
You have made an very interesting superimposing! Could you post the complete picture of that sub? Or tell me where to find.
On this picture it looks like that these blisters are not there. I see complete open flood holes instead!
Is this sub a early Type VII B?

Regards,

Uboatfan

[VIC20]

At development of type VII B they ad these "bumps". This are just open flood holes. But at speed foreward the water could easy get out but nothing or only slow get in.
If someone owns a smal boat he maybe used a very similar thing to get out the water. In german it calls "Selbstlenzer".

I think the Selbstlenzer was invented after WWII by Paul Elvstrøm (born 1928) 

[uboatfan]

Hi VIC20,

that is absolute correct. The Selbstlenzer was invated after WWII.
The basic funktion is similar.
The Selbstlenzer mostly had a additional valve and was foldable to get a smooth hull for more speed.

Regards,

Uboatfan