Tores mailbox VIIC and VIIC/41 operation and technical details

[tore]

Don.
Your first question yes.
Your second question. As indicated on the image the pipe to the expansion box ends in the residue water in the ballasttank. When you are blowing the saddle ballasttank by exhaust you always look for the bubbles indicating the tank is empty. However you cannot empty the tank completly , there is always some residue water in the ballasttank as the Kingston opening is higher up than the end of the expansionbox pipe and as the pipe to the expansion box ends in this residuewater you would not exhaustblow the expansionbox. In ballast configuration the compesating watersystem is sealed off from the tank and is not involved in the ballast configuration.
Tore

[Don Prince]

Hello Mr. Tore,

Since Maciek has posted what looks to be a Type IX C/40 fuel oil tank (left) and ballast tank (right)...  Should we reconsider the connection between the venting pipe and the compensating water pipe coming from the expansion tank? I would think the German U-Boat engineers would keep the same concept for both U-Boats...

One thing to note*


1. IX C  fuel oil bunkers "a" could not be converted to a ballast tank
         tanks FBT 2, FBT 3, FBT 4, R1, FBT 6, and FBT 7 could be fuel oil or water ballast


2. IX C/40 fuel bunkers "1a and 2a" could not be converted to a ballast tank
             tanks FBT 3, FBT 4, R1, FBT 6, and FBT 7 could be fuel oil or water ballast


3. IX C/40 ballast tank design that could be converted to a fuel oil tank has the compensating water line going to the bottom of the tank, and the venting pipe 100 cm above the Kingston and no expansion tank.

Regards,
Don_

[Don Prince]

Hello Mr. Tore,


Wow, I apologize for being such a difficult student...


1. When the saddle tank is in the ballast mode; we have the compensating water line going through the selector valve to the sea through the saddle tank.  Why do we need the line going through the saddle tank to the sea, the Kingstons are already open? It looks like we only need one water compensating line going into the saddle tank?


2. The expansion tank will capture fuel oil at the top during fueling.  As long as the fuel oil is not forced into into the lower pipe in the expansion tank, then that's not a problem. later the fuel oil in the expansion tank will be forced back into the saddle tank by compensating water when the fuel oil is transferred internally.


3. I think the expansion tank is exactly that... during a hot day the fuel oil will expand and apply pressure on the compensating water and the water in the lines may overflow at the header tank.  If the U-Boat dives to a depth where the sea water is much colder, then the fuel oil will condense and additional compensating water will enter the expansion tank from the header tank line. (Here in the US, they say to full up your auto tank in the morning - the gasoline is cooler, in the afternoon the gasoline is warmer and has expanded, so you get less for the dollar).


4. I have attached the drawing of the Type IX C/40 FBT selector valve, If it's the same valve in the Type VII C...  Can you describe how it works?

Maciek, thanks for the drawing...

Regards,
Don_

[tore]

Q. 1. I guess you forgot the base for our assumptions which are confirmed German sources. Maciek quoted previously a German source: Je Sicherheitsrohr. Ist der Drueckwasserschalter zu, stelt das Drueckwasserrohr von restwasser der Tauchzelle ueber Drueckwasserschalter nach aussenbords das sicherheitsrohr dar.
Translated: Re safety pipe. If the selectorvalve is shut would the compensating pipe (in the tank) be connected via the selectorvalve to outboard ( the sea?) acting as a safety (relief) pipe. Hence to prevent venting, the outlet pipe takes the shortest way to the sea thru the tank as you would not have the pipe outside, .
Q.2. When the tank in the fuelconfiguration is recieving fuel, the compensatingwater is forced back via the selectorvalve to the headertank. As you know the filling of the tank is monitored by the check cocks above the compensating pipe end in the tank, particularly towards the end of the fuelling, which is stopped when fuel reach the testcock prior to the fuel reach the compensating watersystem ( expansionbox).
Q.3. If the tank is in fuelconfiguration, the expansion box is in contact with the sea via the headertank and the differential pressure sea/ tank at bottom of the tank would be equal to the weigth of the liquid (seawater) column up to the header tank. regardless the depth. The pressure in the expansionbox and tank might vary depending on the liquidcolumns temperature, salinity etc. but a differential pressure shall always persist.
Q.4. This icon of a selectorvalve is unknown to me, and is not shown on any VIIC plan. I am not familiar with the IXCs, but if you have a selector valve in the position shown on the IXC plan having the outlet to the sea, (outboard), on top of a ballasttank, the selectorvalve would act as a vent. Somehow this selectorvalve must prevent venting, I cannot tell how. In the VIIC system we have assumed a venting prevention by putting the outlet to the sea at the bottom of the tank mentioned above, not confirmed though. It could be worth while to check this item how it works as it would have been a better solution having the outlet under the casingdeck, avoiding the pipe thru the tank.
Tore

[SnakeDoc]

Hi Gentlemen,

I have also attached the drawing with the external fuel tanks and ballast/fuel tanks at the type IXC/40 U-Boat. In my opinion, especially interesting is the drawing of the fuel tank (Treibolbunker), whose piping is similar to the installation given by Tore. On the other side, the arrangement of the ballast/fuel tank (Tauchbunker) is simpler than the corresponding, hypothetical piping of the ballast/fuel tank at type VIIC U-Boat.

To the drawing, I will add the related description from the Type IXC Design Study:

A compensating water system is used with all fuel carrying tanks with the exception of the auxiliary tanks. Pressure on the compensating system is through the medium of a head box in the superstructure. The compensating lines to the individual fuel ballast tanks run directly to the bottom of the tank while the line for the outboard normal fuel tanks (my note: that is Treibölbunker a) leads into the small salt water niche (1.5% of fuel tank's volume) in the bottom of the tank; a line then leads from the top of the niche to the bottom of the fuel tank. [...]. Test piping with an overboard discharge leads from the bottom of all the normal fuel tanks, and from a point approximately 4 inches above the top of the flood opening on the fuel ballast tanks (my note: that is Tauchbunker). These test lines are normally used as salt water discharge lines when fueling - not only to indicate when the tank is filled with oil - but mainly to prevent possible contamination of the compensating water lines with fuel oil. All piping runs external to the pressure hull.

--
Regards
Maciek

[SnakeDoc]

Q. 1. I guess you forgot the base for our assumptions which are confirmed German sources. Maciek qouted previously a German source: Je Sicherheitsrohr. Ist der Drueckwasserschalter zu, stelt das Drueckwasserrohr von restwasser der Tauchzelle ueber Drueckwasserschalter nach aussenbords das sicherheitsrohr dar.
Translated: Re safety pipe. If the selectorvalve is shut would the compensating pipe (in the tank) be connected via the selectorvalve to outboard ( the sea?) acting as a safety (relief) pipe. Hence to prevent venting, the outlet pipe takes the shortest way to the sea thru the tank as you would not have the pipe outside, .

These assumption are also confirmed by British report on HMS Graph (ex-U 570), quoted previously by Tore:

The compensating water pipes are led from the expansion tank (head tank in fact, my note) in the conning tower casing through double-seated valves to the small expansion tanks fitted at the bottoms of the fuel tanks. The double seated valves must be either in connection with the expansion tank (head tank in fact, my note) or with the sea. The expansion tank is always in open connection with the sea and thus the fuel tanks are always equalised and the only compensating water pressure which can be applied is that due to the head of water in the expansion tank (head tank in fact, my note). This arrangement is necessary where direct blows are fitted and avoids the possibility of straining the tanks due to high pressures.

and

The water passes down to the tank through a double-seated valve which admits water to the tank either from the expansion tank (head tank in fact, my note) or from the sea.

However British made some confusion, using the "expansion tank" term for the head tank in the conning tower as well as for expansion tank at the bottom of the fuel oil/ballast tank. I have made some annotations to point which tank is which.


Don, I would also think that German engineers would keep the same concept for both types of U-Boats, however there are clues that they wouldn't.


--
Regards
Maciek

[Don Prince]

Hello Mr. Tore and Maciek,


I would like this iteration of the expansion tank system to be the final change to Skizzenbuch on this subject.


1. I went back to Mr. Tore's latest drawing.
2. I re-drawn the selector valve in the Fuel Oil Mode and the Ballast Mode.
3. I got the expansion tank pipe below the Kingston's highest point (the pipe is always in the water).
4. In the Fuel Oil Mode the expansion tank is in connected to the header tank through the selector valve, and while submerges it is in contact to the sea at the header tank.
5. In the water Ballast Mode, I corrected the selector valve and Identified the Safety Pipe.


If I understand the function of the safety pipe in the Ballast mode; during a HP blow the ballast water is forced out though the open Kingstons, and into the expansion tank as well, and you don't want that thin metal tank damaged!  So the connection at the selector valve to the safety pipe which drains to the sea provides the means for pressure relief. Excessive pressure from the HP Blow forced water into the expansion tank through the compensating water outlet pipe (backwards water flow)...


Gentlemen, If anything is not correct; text or the drawing, then please let me know!


Regards,
Don_

[karel]

Hello friends.  Just wanted to leave a screenshot here of the game that we are building. Again, big thank you for all of you here for helping me to build this thing.

[tore]

Karel.
Amazing atmosphere. The handwheels of the exhaustblowing panel is a bit on the large side. When you are blowing the tanks by exhaustgas the tophatch is normally open and people are on the bridge. During daytime you`ll get a welcome faint glimse of daylight coming down to the hatch opening.
Tore

[karel]

Thank you Tore.


Yes, we had to exaggerate a little bit because of today's state of technology. Having bigger handwheels makes it more comfortable for a person to grab this object with motion controllers and also helps keeping physics a bit more stable. Game engine physics tend to go nuts with these kinds of interactions. Just to give better context. The game is going to be played on this virtial reality device https://www.youtube.com/watch?v=qYfNzhLXYGc&t=135s


As for daylight. This was another sacrifice we had to make. Virtiual reality game must run minimum at 90 frames per second in order to avoid jitter in the headset. This means that to keep the visual quality that we want, we have to cheat here and there. This includes all lighting which will be baked into the environment. This sadly means no realtime light, when i open the hatch i am not going to get sunlight. These are just sacrifices that we must take in order to make it able to run on current gaming PC. But years from now, down the road we can change all that when gaming PC will become more and more powerful.

[tore]

Karel.
Interesting problems. Anyhow operating an Uboat in the artic would never offer a sunlight down the hatch, only dim daylight, but nevertheless highly appreciated after being days submerged.
Tore

[tore]

Don.
I am afraid we have not yet achieved a complete confirmed arrangement of the saddle tank fuel arrangement. Maciek has provided a few interesting informations although I agree to his comments you cannot copy details from a IXC to a VIIC, I am tempted to discuss the details of the crosssection of the fuel/ballast arrangement on the imaged shown by Maciek. On the image below I have tried to show details which might be applicable for a VIIC.
The "oil drain" from the inverted U-tube might not go up to a drainvalve below the casing deck,  we have no german confirmation of such arrangement, I guess the arrangement with a small swan-neck shown on the IXC cross sectiondrawing is possibly an appropriate alternative, simple and reliable. The possible oilcontamination is lead by a small swan neck pipe from the  overflowpipe from the expansion box ascending and eventually  merge with the fuel in the tanktop. A fuelling check is done with the standard fuel checking.
The expansion box arrangement, light blue on the sketch, could very well be used on the VIIC saddletanks as it matches the written descriptions.
The selector valve arrangement is a puzzle as the icons on the systemplans are not identical, the IXC plans have obviously another selectorvalve design allowing the valve to act as relief valve without venting the tank thus avoiding the long pipe down the sea. Our latter pipe with sea outlet has yet to be confirmed for the VIICs.
Hopefully somebody might come up with some info/images allowing us to have a confirmed arrangement for your Skizzenbuch, until the our assumption remain unconfirmed assumptions. Sorry about that.
Tore

[Don Prince]

Hello Mr. Tore,


I have been confused about the pipe going to the sea from the selector valve...  After Maciek came up with the type IX tank configuration, I created a drawing and then deleted it because of our further discussions. However, I went back to my MS trash basket and restored the image. 


This is the drawing... Do you think this could be the basis for a different approach?


Regards,
Don_

[SnakeDoc]

Hi Karel,

Hello friends.  Just wanted to leave a screenshot here of the game that we are building. Again, big thank you for all of you here for helping me to build this thing.

Great work. However, if you want to model type VIIC U-Boat (not a museum boat in Laboe), you should pay attention to some modern modifications, for example the control room periscope. The current periscope in the U 995 control room is a post-war type ASR C/13 attack periscope, taken from U-Hai or U-Hecht.
And not only ocular box is replaced, whole tube, together with periscope head is from the attack periscope.
See the attached drawing.


The original ocular box can be visible on this photo (provided by Tore):
http://models.rokket.biz/index.php?topic=921.msg19664#msg19664




More details in this article.


--
Regards
Maciek

[Don Prince]

Hello Mr. Tore,


What do you think about this version of the saddle tank compensation system?


Regards,
Don_