Tores mailbox VIIC and VIIC/41 operation and technical details

[Katuna]

Thanks for posting those Don. I think I have the German version somewhere in all my info but not the English. It's great to see (and have) a complete book.

[Don Prince]

Hello Mr. Tore,

I was thinking about the external canisters that held the spare torpedoes below the deck... The G7a torpedo weighed about 3,369 lbs and the G7e weighed about 3,534 lbs; a torpedo canister would displace about 4,032 lbs of water. So, I figure with the weight of the canister and the air space at the end-points of the torpedo in the canister; there was about neutral buoyancy on the loaded tubes below the deck. The G7a (T1) torpedo had a negative buoyancy of about 605 lbs and the G7e (T2 and T3) was about 597 lbs negative buoyancy.

However, my first thought would be when the torpedoes were moved inside the pressure hull, then the torpedoes weight is still on the U-Boat, only now inside the pressure hull. When the torpedo is fired, then the water from the torpedo tube is drained into a torpedo trim tank. Therefore, there is no weight change on the U-Boat. You now have the water in the torpedo trim tank countering the emptied torpedo canister below the deck weight loss.

Did they seal the canisters after removing the torpedoes?

Then the weight has not changed on the U-Boat; the torpedo was just moved inside the pressure hull. When the torpedo is fired, then water from the torpedo tube is pumped into the torpedo trim tank to maintain the balance and the U-Boat's trim line.

However, I would think if they closed the canisters, then there would be two (2) sealed canisters containing an air bubble creating a diving issue.

I believe this would be a lesser issue with the Type VII U-Boats with just two (2) external torpedo canisters, but on a Type IX U-Boat with ten (10) torpedo canisters where this could create a serious diving problem...

What do you think...

Regards,
Don_

[tore]

Don.
Weight changing is a never ending story of a submarine operation, this refer not only to torpedoes, but consumables like all the items which involving the needs of 46 persons during weeks. There are many ways the weights influences the behaviour  of the vessel, like the trim moments ( alongship distances from the centers of gravity) and heights ( stability, metacentric heights.). In case of liquids, free surface effect might create problems. Hence 100% water compensated fueltanks were used. Thus a number of elements are involved. Generally you are able to control a submarine dynamically ( by speed and hydroplanes or/and by filling and draining trim tanks. In order to simplify the matter you have general rules like compensating for free surface effect by having containers either completely full or empty, using experience by compensating weight movements inside the pressurehull, like shifting crew from nightmode to battlestations (divingstations). On the U-995 you had to pump 400 ltr water from aft trimtank to fore. We did away from the torpedo containers in the casing, but should assume they would be flooded unless the weather would be bad and hence it could be a stabilityproblem surfacing ( critical just breaking the surface ). If you were entering hostile waters you would fill the Q tanks ( untertriebdzelles) to be able to dive quickly. As so many others things in life, experience rules and the COs judgment was the base of the procedure. In fact you could not make strict rules unless you involved the whole picture of the mission of the submarine, as one step would interfere the others.
Tore

[Don Prince]

Hello Mr. Tore,


If the External Torpedo tanks (Aluminum) were open, then they would flood when diving and emptied when on the surface and not creating a problem in bad weather...


Thanks again, Regards,
Don_

[Don Prince]

Hello Mr. Tore,

I was online with a model builder and he had what looked like rain gutters on his U-Boat (U-995) and the diesel exhaust looks to be wrong as well. I have attached a few photos... What do you think?

He also has a diesel exhaust like the last photo...

Regards,
Don_

[Don Prince]

Hello Mr. Tore,

Do you have any photos that show the blister on the port side casing for the schnorchel air intake, and the exhaust piping above the deck in the starboard side. Marcus, the model builder seems to believe the all was under the deck on U-995 (Laura S-309)?

Regards,
Don_

[tore]

Don.
It is not easy to preserve a full open air monument like U-995 for many years unless you take corrosion precautions deviating from the original. One of the big problems are corrosions between the casing and pressurehull, hence the drain holes and the gutters on the museums U-995. I dont think the drainholes are made through the pressurehull The drains have been modified many times through the years as can be seen on my image below. Another issue is the corrosion of the pressure hull derived from galvanic corrosion while the U-995 was "stored" afloat without sacrificing elements. leaving serious caverns in the pressurehull. I really don`t see the point in copying these corrosions on a VIIC model as in such condition the VIIC would not be seaworthy. Another tendency is to exaggerate the tiny rivets in the casingplating, which sometimes gives the model a look of a tank from WW2.


Tore

[tore]

Hello Mr. Tore,

Do you have any photos that show the blister on the port side casing for the schnorchel air intake, and the exhaust piping above the deck in the starboard side. Marcus, the model builder seems to believe the all was under the deck on U-995 (Laura S-309)?

Regards,
Don_

Don.

In may 1945 U 995 was installing her schnorchel at the submarine base in Trondheim, here is an image showing the final stage of the installation with the airelbow in the casing is protruding out from the casingside, this is the only part of the snorchelair inlet pipe out of the casing, the remainder is inside. Remark the float on the top of the mast has a ringfloat whereaes the present museums U-995 has a hingefloat.

Tore

[tore]

Hello Mr. Tore,

Do you have any photos that show the blister on the port side casing for the schnorchel air intake, and the exhaust piping above the deck in the starboard side. Marcus, the model builder seems to believe the all was under the deck on U-995 (Laura S-309)?

Regards,
Don_

Don.

In may 1945 U 995 was installing her schnorchel at the submarine base in Trondheim, here is an image showing the final stage of the installation with the airelbow in the casing is protruding out from the casingside, thisis the only part of the snorkelair inlet pipe out side the casing, the remainder was inside. Remark the float on the top of the mast has a ringfloat whereaes the present museums U-995 has a hingefloat.

Tore

[Don Prince]

Do you remember if the exhaust piping was above the deck?

[tore]

Don.
Here is the schnorchelsystem, the yellowpart of the exhaust is protruding up on the casingdeck to allow place for the exhaustblowing panel, the valves are, as you know, operated inside the pressurehull in the controlroom.
Tore

[tore]

Don. An image of KNM Kaura ex U-995 1953 where the Schnorchel exhaustbend is clearly seen on the casingdeck.
Tore

[Don Prince]

Hello Mr. Tore,

I found a very early photo on the subcommittee.com website of U-995 and I'm now not sure about the 'Drip Line". The original photo of U-703 looks like perhaps like a "Drip Line" existed? However, the early photo of U-995 leaves me unsure... Perhaps they closed the "Drip Line" during the restoration, and then they decided to re-add the drainage later after they seen a water buildup... What do you think?

Regards,
Don_

[Don Prince]

Hello Mr. Tore,

After blowing up the image, it looks like when they rebuilt U-995 that they plugged up the "Drip Lines" with small rectangular patches (welded over the drain slots)...  Then when they ran into water backup issues, they cut rectangular holes in the casing and added the gutters. What do you think?

Regards,
Don_

[tore]

Don.
 I wouldn`t trust the present execution of the museums U 995 as there are many modification related to the safety of the visitors. F inst. the foreship floodgates are welded shut due to people starting to climb the casingside. The image you are posting seems to be of the welded type casings, the original is riveted. I cannot remember the details 100%  but am reasonable sure there were no "gutters". The aft fairings of the saddletanks on some VIICs were equipped with floodgates as shown on my image.
Tore