Tores mailbox VIIC and VIIC/41 operation and technical details

[tore]

Frank.
I see there is another thread discussing the KNM Kya. Kya Ex U-926 was a VIIC and not a VIIC/41 class. But she had an Atlantic bow and was the first VIIC  serving in the Norwegian Navy as from January 1949. We had three VIICs operating in the Norwegian Navy, one was a VIIC/41, KNM Kaura ex. U995. All three VIICs were modified before entering into the norwegian navy. One of the most visible change  was changing the conningtower casing allthough many believe this was just the old 1939 tower, it was different as can be seen from my image below.
I served as the engineering officer (chief engineer) on both KNM Kaura ex. U-995 and KNM Kya ex. U-926. and knew ltn.cmdr. Bjørn Ellingsen very well.
Neither the U 995 nor the U 926 were fitted with the balkongeraet when in frontline serving in the norwegian navy, they were fitted later, anyhow after 1956.
Tore

[zhuravlik]

Mr. Tore,
Disregarding tower, wintergarden and hull thickness, wich are the main differences between VIIC and VIIC/41?
My intention is to build KNM Kya as the maximum evolution of a type VII i.e. with an idrodynamic sail and balkongerat.
Sort of european GUPPY program.


Best regards,
Frank

[tore]

Frank.
For a layman it is hard visually to see any outside differences between the two types VIIC and VIIC/41. The latter some tens of cms longer overall, mainly due to the atlantic bow which I guess is incorporated in the Revell Kit. The main difference is, as you say the stronger pressurehull and increased max. divingdepth. The stronger pressurehull increased the weight and as no change was made as to the mainengines some efforts was made to compensate this by removing and/or make lighter equipment whenever possible, but again no visible items. It might be that the max speed would be a fraction of a knot lower, but we did`t notice much difference. Some are of the opinion that the VIIC/41 had the new compass housing in front of the tower, generally not so, U 995 had the old rounded type although they have substituded this with the new type on the museums U-995, don`t use the museums U-995 as a reference as many details are unfortunately not correct.
The trouble to upload the images on this site is due to an upgrading they just had whereby all the images disappeared. They are busy with the problem, but I guess  it`s difficult to resolve. As a substitute they are going to make some sort off a gallery they told me.
 If you are in need of any images on my thread let me know and I get it for you.
Tore

[zhuravlik]

Mr. Tore, you are very kind.
So, the hull's mold lines are the same.
I would need every sail picture you have because i need to draw a plan for Kya's hydrodynamic sail.
You say that balcongerat was added after 1956. Was the boat still in frontline service?


Best regards, Frank.

[tore]

Frank.
The ex German VIICs finished in our navy as operational submarines 1960 and are since then was used for training and research. Unfortunately I don`t have any images of the new tower of Kya, but am aware of you needs and shall react if I get some. 
 As to the difference between the old standard VIIC bow and the Atlantic bow you may study the images below to check your buildingkit. Basicly the bow was raised a few cms and they put in a flare to the bow to improve the pitching behaviour in heavy sea. I guess there were several steps before the final solution.
Tore

[Don Prince]

Another view of the "Atlantic Bow" on U-995...


Regards,
Don_

[tore]

Frank.
I just checked the Revell 05100 kit which is a VIIC/41 so it shall fit your requirement very well. Only make sure the schnorchel has a ringfloat air inlet on top, not a hinge type as they put on the museums U-995.
Tore

[tore]

As next step in the developement of the Kya sail (or fin as we say it) I am posting an image of the testing of the tower on the class which relieved our K class (VIICs). The name of my old Kaura S 309 ex. 995 was transferred to the new submarine S 310 KNM Kaura developed in cooperation with the Germans and named the Kobben class ( Seal class). Below is the final solution, this class is later relieved by the Ula class, which now is planned to be relieved by another new class. Submarines warfare is expensive.
Tore

[tore]

One of my most read topics which disappeared during the last upgrading of the site was the effect on ballasttanks pressure related to the diving/surfacing angle of a VIIC. The standard correct divingangle should be about 7 degrees. An easy check on the correct divingangle would be as the top of the bridge wind deflector is at the watersurface the top of stern (in the RN called dutchess ass) should be at the surfacelevel as well. The relativly high pressuredifference between MBT 1 and 5 can easely be seen on my image below. At a moderate diving angle of 7 degrees there is a pressure difference between the floodgates of 0.7 kg/cm2. At a divingangle of 25 degrees you get a pressure differerence of 2 kg/cm2. Why is this important? Appart from the difference in stresses on the pressurehull, the requirement of blowing the ballasttanks changes, in case of an emergency blowing the MBT 5 would need 2 kg/cm2 higher airpressure (thus more air) to blow the same amount of water as on MBT1. If not adjusted the boat would get even a worse trim which might be dangerous.
When surfacing the ideal surface angle would be about 2 degrees by that the floodgates of MBT1 and 5 would be at the same level, 3.5 meters. This means when you start blowing the MBTs by exhaustgas  the counterpressure in boths tanks are the same, the saddletanks counterpressures however are the lowest so you start blowing these tanks ,then you switch over to the MBT 1 and 5 until you get the deepest MBT3 at an acceptable counterpressure.
When blowing the ballasttanks the air/gas takes the easiest way eg. the lowest counterpressure thus you have to compensate for the pressuredifference otherwise you bagger up your trim. This is why you have all the individual adjustingvalves in the controlroom for each ballasttank, both for exhaust and air blowing.
Tore

[Don Prince]

Here is another one of Mr. Tore's drawings...
Regards,
Don_

[tore]

The sketch shown in Dons post indicates another problem with a submarine as well. Apart from the obvious disadvantages of trapped air in tanks which might leave treatcherous bubbletracks you have the dangerous and undesired effect called the free surface effect. As long as a tank ( or compartment) is either full or empty there is no such effect, however when partly full of liquid there is an unstable situation as the center of gravity moves back and forth as the pitch, heave, roll, surge, sway or yaw varies. The effect might create a larger problem for a submarine than a surface vessel. To avoid this, the submarine is designed to limit free surfaces as much as possible, hence you have watercompensated fueltanks and try to keep the ballasttanks either full or empty. The residue venting of MBT 2 helps to fill the tank completely and thus to get rid of the free surface effect as well.


Tore

[Don Prince]

Hello Mr. Tore and All,


I uploaded "Skizzenbuch 11 x 17 - M + Index.pdf" to dropbox.  I added the Index to the back of the book and places the Index Page 461 in the Contents listing.  This website section looks to be fairly quiet for awhile.  I guess some time this fall I will be working with the publisher on the Type VII book.  Once finished, I may start another book on the Type IX C.  I currently have the drawings for the electrical schematics, and I have ordered the mechanical schematics from the Bundesarchiv via the Silke Archive Service in Germany... I believe we can make this website come alive again! 


Regards,
Don_

[tore]

Don.
I read you last version of the Skizzenbuch and like your pages having roman figures describing diving and surfacing procedures, which is correctly understood. One detail though, when diving and surfacing using the tanks, you normally are manning the diving stations. This means a lot of people are moving around particulary from the crew quarters in the fwd. torpedo room to the aft control room, engineroom and aft torpedoroom. This has influence on the trim and you have to compensate this by using the fwd and aft trimtanks. So prior to giving the orders divingstation, you pump water from aft trimtank to fwd. trimtank, our experience was you needed approximately 400 liters, to compensate for the moving of people. Hence the trimtanks take a part in the diving and surfacing procedure as well. Likewise when the battlestation (which are almost the same as divingstation) orders are given. When the situation is cancelled you operate the trim tanks in the opposite way. In fact when being submerged you reacted on the first order: "pump 400 liters from aft to fwd." realizing it will soon be followed by diving station.   
Tore

[tore]

Looking through old papers in my files I came over this cut I made from the french newspaper Le Figaro March 16. 1972. I remember it well, I was on  a business trip in France and with my hotelbreakfast I got the le Figaro morningpaper, to my astonishment I saw my old submarine KNM Kaura ex-U995 hanging in the air on the frontpage. I cut it out and saved it. For those of you mastering french you can read the story bearing in mind in spite of 27 years had passed since the end of WW2 there was still some feeling of the event of placing the submarine on the concrete foundation at Laboe.
Tore

[Don Prince]

Hello Mr. Tore,


During a dive you have people moving to their dive stations and you seem to indicate that 400 liters of water is pumped from the aft to the fwd trim tank to compensate for the change in the U-Boat's trim.  I believe I understand these trim adjustments.  all personnel will remain at their assigned locations while submerged.


However, during an emergency dive addition crew personnel may move to the fwd torpedo room to give the U-Boat an additional bow down trim to accelerate the diving process. 


1. Who gives the orders for that movement, or is it an understood procedure during an emergency dive?
2. Would they ever pump more water from the aft trim tank to the fwd trim tank for additional bow down trim?
3. Who would give such an order?
4. Who would act upon those orders?


Regards,
Don_