Tores mailbox VIIC and VIIC/41 operation and technical details

[karel]

Hi Tore, Don, Maciek.  I am new member to this forum and hope if you don't mind for me asking a lot of silly question about the operations of VII.


A little introduction about me. My name is Karel and i am in the same situation like Mark, i am also developing a submarine game. Only i am not trying to recreate physics and 1:1 since my experience will be a bit different. It is a game that is played trough virtual reality headset (Oculus Rift and HTC Vive) and will have a multiplayer element. What i am trying to achieve is to recreate the feeling of being inside the submarine. For the past 2.5 years me and my team have been recreating the Interior of VII u-boat. Since the game is built ground up for virtual reality, we had to turn a lot of attention to all these small details. Of course we cannot recreate 100% of the interior details with the top visual quality because no computer would be able to play them. (VR game needs to run 90 frames per second) 


As for the gameplay. Since the game can be played alone, or with a friend we wont put player trough heavy process of an actual submarine control. Its too complicated and would need more people. Since players are in virtual reality and have hand controllers they have to physically turn all those Valves and vents. So instead we are going for the easier and fun route where 1 player can manage the control of the U-boat if he needs to. But.. this opposes another problem, since we want the u-boat interior to feel authentic we still want to model at least 60-80% of all the control elements and. Easy fix for them would just to have these as props, an eye candy that cannot be interacted with. Again problem is that in virtual reality if you already have some interaction build for certain valves, then user automatically will assume that everything is intractable. So we decided that every valve has to have some sort of meaning, so when player turns a valve that regulates oxygen levels in different compartments then he/she is able to do so. We can easily add some sound feedback, like a hissing sound that travels trough the oxygen pipes. This will give no affect to gameplay itself but still adds agency to the player making him/her feel that every action has a meaning (even if this meaning has no gameplay value)


Other aspect would be purely educational. They could walk around the boat and learn the meaning of every operation that was done inside the u-boat.  What i would like to avoid is making a gross errors like confusing flood valves with oil valves and etc.


https://www.youtube.com/watch?v=hYMoLe5ZSaQ - here is the video of the game.  It is still a very much a work in progress. Also do not mind, no operation there is historically correct. I needed a prototype asap and many of these things were made up for speed purposes. Now that our u-boat is in the finishing stages it is time to start researching about the controls.


So this is the reason why i joined this forum. I found you brilliant people and was hoping to ask many many questions about what some or other instrument inside the u-boat does. Then i could use this information to create a "semi-realistic" virtual tour of the u-boat that has all the objects intractable.
I am aware about the book that Don is making and it would save me months of research work but sadly it is not available yet.
So i am hoping that you gentlemen do not mind if i stick around and ask many questions.


----Questions


My first question about all those lost image materials that come before page 200. Are all these lost, i cannot see them? When i download the attachment they seem to be broken. Seems that the site was offline and after coming back all this information is lost?


My second question is about attacking other boats. As i understand that neutral buoyancy was almost impossible to achieve. Does that mean all attacks trough the periscope must be done when boat is moving because then hydroplane operators can fine tune the depth?


Third question is about the ballast. When i am filling all MBT1,2* MBT2, MTB3, 2* MTB4 and MBT5 100% and not touching the negative buoyancy tank.  How deep does the boat go until it starts to approach its neutral buoyancy?


Thank you. And i apologize for the wall of text

[tore]

Karel, welcome to the forum and my mailbox, I admire you intentions and shall try to help where I can. I am afraid the lost images up to page 200 is lost due to a crash of the system but the knowledge is  here and I have quite a few of the images in my file so just shoot you questions and we`ll see what I can do.
Second question. Neutral buoyancy is not necessary for attack in fact sometimes not even desireable. If your submarine is weightless it requires a small force to move it and your are unstable. As in open sea you generally have swell and waves moving the submarine you want to counteract these movements by dynamically controlling ( by hydroplanes and speed) the submarine. Attacking at periscope depth is the most common attack and you are relying on your hydroplane operators and the trim. The trim (regulating tanks are filled according to experience, calculation and weather) and the hydroplane operators using their hydroplanes watching the Papenberger, a depth gauge having a scale where you can read the position of the attack periscope in relation to the sea surface. See attached image. I guess the only time you are using a accurate neutral buoyancy is when hiding either for escape or observation. You search for an interface between to different densities of water ( sonar mirror), put you submarine under the layer, adjusted to neutral buoyancy trim, shut down all machinery (dead silent) and adjust minor differences in displacement by lowering and raising the periscopes. This can be done silent if you top up your hydraulic accumulators and use the stored hydraulic energy to lower and raise the periscopes.
Tore

[tore]

Karel, I realize I forgot your third question. When the main ballasttanks are not used for fuel, they are only used for diving the submarine and do not participate in the trimming. Prior to the diving, the regulating tanks are adjusted to the calculated desired trim submerged at the requested depth. When diving requesting a quick dive you use the Qs ( Untertriebzelles) to overcome the "surfaceresistance" for the first part of the dive. The Qs are blown as soon as you are submerged, generally at some 8-10 meters and the submarine is at the right trim at the required depth if the regulating tanks are adjusted correctly, if needed the regulatingtanks can be corrected when submerged by the main ballastpump. If you want to take the submarine further down, the pressurehull is compressed and the displacement is reduced and you loose buoyancy, this has to be compensated by pumping out water from the regulatingtanks 1 and 2 port and stb. corresponding to the loss of buoyancy. For a VIIC this would be about 100 liters seawater per 10 meters. As you probably know, a pair of the regulatingtanks 1 can be used for fuel, which reduces the flexibility of the regulating tanks when in fuel configuration. The same happens when MBT 2 and 4 port and starboard are in fuelconfiguration, which means the ballasttanks are partly filled with diesel fuel having a specific weight less than seawater. You have to compensate this by using regulatingtanks 2 port and starboard which cannot be used for fuel. All told, the regulating tanks plays an important part in the trimming of the submarine and not the MBTks as long as they are not in fuelconfiguration.
Tore

[karel]

Thank you Tore. Based upon your feedback i think that i have made pretty good diving system for my game. Its not 100% realistic, but still has some complexity and is not "push one button to dive" system.

About the tanks itself. I read somewhere (possibly in this thread) that all the diving tanks had to be empty or full. There was no in-between solutions like only flooding 50% of a certain tank. Why was it that way? Did the boat become unstable?

Another theoretical question about neutral buoyancy. It may be confusing but i try to explain. I apologize if i do it badly

Lets say commander achieves near neutral buoyancy with the slight force that moves the boat up. Is the upward momentum a continuous force and the boat will eventually reach near the surface? Theoretically i think that the upwards movement should continue to happen until the boat reaches shallower depth where pressure is smaller, and the weight from ballast tanks will become an issue again and makes the boat sink again.
Is this right?

Thank you.  Btw. I love your name. Tore in my native language means the word "great"

[tore]

Karel.
The reason for having the tanks either empty or full is to avoid what we call the surface effect. When you have only partly filled liquid in a container which is moving you get a rapid shifting of the center of gravity of that tank as you create a local wave in the container and a submarine is susceptible to these movements. To avoid that, you keep the tanks for liquid either full or empty. As a consequence of this effect all the fueltanks are always full eg. seawater compensated, meaning you let the seawater fill the empty space left when you are consuming the fuel. The fuel " float" on the top of the compensating water as seawater has a higher specific gravity. In those cases where you cannot avoid partly filled tanks, like regulating tanks, you "chop up" these movements by fitting ripple/splash bulkheads in the tank allowing the liquid to move but only in smaller quantities. Further you try to place these tanks as close to the submarines gravity/buoyancy center as possible reducing the impact moments. There is no in between solutions, but as you gradually fill the fuel tanks and the ballasttanks in fuel configuration with seawater, the weights and moments changes thus you have to calculate and adjust that by the regulating tanks and some times even trimtanks.
If the submarine is having a slight positive buoyancy at a certain depth, it don`t only ascend, but shall have a slight acceleration upwards as the hull is expanding increasing the displacement. If any residue air is left in the ballasttanks this air shall expand as well and force the ballast water out of the Kingstons increasing this acceleration. Eventually the submarine shall break the surface sometimes higher than equilibrium due to inertia forces before she rest on a surface draft corresponding to the weight /displacement balance. This could be an uncontrolled  stability position as the MC (Metracentric centre) is changed. As you know this procedure take place when surfacing, you raise the submarine dynamically to periscope depth, then by HP air blow your MBTs only partly to save HP air resulting in being only semi surfaced and unstable before you start blowing, by the diesel exhaust, the main ballast tanks at a certain sequence until you are fully surfaced.
As to my name your native tongue is not far off. The name is from the Viking god Tor, who is the God of thunder and lightning. I guess he was pretty big.
Tore

[Don Prince]

Hello Mr. Tore and All,


My wife, Maureen sent me this link from her cell phone...  The final resting place of U-576 a type VIIC that was lost in 1942 off the North Carolina coast.

http://www.dailymail.co.uk/news/article-3774630/The-ghosts-U576-German-U-Boat-30-miles-coast-North-Carolina-72-years-sank-Nazi-campaign-terror-44-soldiers-entombed-inside.html


Regards,
Don_

[tore]

Don. Reading the newsarticle I noticed they state the wreck was located August 24. 2016. I guess it has previously been published she was located 22. October 2014. One of her ballasttanks was damaged, hampering her diving and surfacing capabilities prior to her last attack. I guess the damaged tank could probably  have been one of the saddletanks.
Tore

[karel]

Tore.

Thank you for explanation. I added this behaviour to my diving system. I have read the word "Kingston" here a lot but since pictures are gone it is hard to put it into context. Is this some kind of valve? Do you have a picture of it?

Also trying to figure out submarine speed. Wikipedia says that under water the max speed was 7.6 knots. Was that speed always constant or did it decrease when submarine went deeper? Could it actually run at 7.6 knots when at 155-200 meters?

[tore]

Karel. Kingstons are named after a British engineer living in the latter part of 1700 who invented the valvetype. It is merely a bottom valve allowing sea water to enter into any ships hull. For a submarine this means specifically the bottom seavalves of the ballasttanks allowing seawater to enter the tanks when diving. Kingston are usually always open when the submarine is at sea and shut when alongside in the harbour for safety. They are cumbersome to operate by removeable cranks which are placed on the square of the valvestems, usually in the controlroom. Theoretically you could sink a submarine if laying alongside by opening the ballasttank vents if the kingstons were open. Sometimes you would shut the Kingstons when depthcharged preventing the shock waves to enter the ballastanks. Below is my model of KNM Kaura ex U-995 showing the Kingstons in this case square flapvalves in the bottom of the saddletanks and MBT 3.

[tore]

Karel. Speed of the VIICs submerged . Speed submerged (or may be the water resistance) is not changing noticeably within the submarines operation depth range, and depends thus primarily on the power available at the propellershafts. The VIICs and many of the WW2 submarines had a low submerged speed as the e motors did not have the powers to exceed the speed mentioned by you. The German submarine tactic "Wolfpack"  would be to gather several Uboats where they assume a convoy would pass, carry out the attack requiring slow speed. After  the convoy passed, reload the torpedoes, when ready, proceed on surface at high speed 17-18 knots overhauling the slow convoy  (7-12 knots) by powerful diesels, dive ahead of the assumed course of the convoy and repeat the attack. Modern submarines of today are differently designed and adopted to different tactics which requires higher speed submerged.
The E-motors were not a constant power motors and the speed and direction of rotation varied, in fact as the diesels of the VIICs after 1942 had the reversing removed, the E-motors were the only motors used for maneuvering able to revers and having variable speeds. Finally the e-motors were used as generators as well, driven by the diesels charging batteries solely or combined when diesel cruising on the surface.
Tore

[SG]

Great piece of intel, beautiful uw footage shots and original b/w pics, Don. Thank your wife on my behalf!
 

[karel]

Really good information 


So i think that my diving system is pretty good at the moment. Played in virtual reality today and the new diving system added a new dimension to the gameplay. Instead of going to x depth and calling it a day, i know have to keep the boat in balance and in trim. If i constantly do not watch and adjust my bearings i risk to sink the boat or surface. Lets just say that evading a depth charge became much more complicated. Hopefully i can get multiplayer working correctly so people could divide up the tasks in the sub. Running alone in sub, adjusting instruments, keeping track of the enemy and evading, even though it is all super simplified it can be a daunting task to handle alone.


Tore. Are you able to tell me how fast did those tanks filled up with water? I guess different tanks had different speeds since their size were not the same.  I am mostly interested in tank3, tanks 4 and 2, tank1, tank5, and negative tank. These tanks are represented in my game.
I also have a trim tanks represented in the game that shifts gravity from one end to another if needed. As for gameplay reasons i had to add another "special unrealistic cheat compensating tank" that just holds the boat at neutral buoyancy at periscope depth. Otherwise it would be impossible to play this game as a single player experience since you would need to constantly jump between the hydroplane controls and periscope.

[tore]

Karel. You cannot fill the ballast tanks independently as you shall upset the trim both atwartship and alongship. What matters in real life is how fast you can dive in emergency. The ballasttanks 2, 4 port and starboard as well as MBT 3 have all Kingstons dimensioned  for the capacity of the tank and a quick filling, MBT 1 and 5 have no Kingstons but free flood gates with ample dimensions, adopted to the quickest diving time. All the MBTks particularly MBT 2 and 4, and MBT 3 have quick vents by pull down handles, MBT 1 and 5 by hand wheels, all situated in the controlroom.
 An optimal quick dive can be obtained by following a special procedure. When approaching hostile waters you fill the Qs and increasing the draft, but primarily to assist to overcome the "surface resistance", the regulating tanks adjusted to the COs request for a buoyancy at a particular depth. At the order for an emergency dive you open the vents for MBT5, MBT3,MBT2 and 4 port and stb, for MBTs 2 you open the residue air vent waiting to vent MBT1 to assist the bow down angle. When the boat start to dive bow down you normally open the vent for MBT1, the boat is controlled dynamically ( by speed and hydroplanes)at angle of 8 degrees to prevent the stern to be  too high above the surface, a rough control by the periscope would be the towers wind deflector is at the sea surface simultaneously with the aft end of the boat. At 8-10 meters you blow the Qs and the boat has a required buoyancy at f.inst. periscope depth. By following this optimal procedure you can obtain a diving time of 30 seconds which is pretty good and considerably quicker than f.inst. a IXC.
Tore

[karel]

Really appreciate your input Tore.

Few questions about regulating tanks. When you need to correct your regulation when submerged, you can do it so at the main ballast pump. Can you give me a brief explanation how this was done? I am looking at the screenshot and see bunch of red valves lying on the floor. Did these Valves all work in a combination? Lets say i need to pump more water to aft and thus only rotating certain Valves.
Also doing trim when you are surfaced. Did you use same valves or was the trimming on surface done differently?

Thanks,
Karel

[tore]

Karel.
The regulating tanks are used all the time and the operation of same is in the controlrom. The regulating tanks can be operated in many ways by:
1. The main ballast/bilge pump being a two stage sentrifugal pump. The 2. stage used to discharge to sea at greater depths. 
2. The trim/aux. bilge pump being a pistonpump.
3. By hp air.
Further regulating tanks 1 can be used as fueltanks as well.
This require a somewhat complicated pipe and valve systems to handle all the alternative and fairly confusing to a layman so I guess I should start with alternative 1. being the most common.
 On my image below you see the pipesystem for the main ballast pump, capacity 1300/1465 liters / min. against 15 meters. and the 4 regulating tanks in seawater configuration, green regulating tanks 2 and yellow regulating tanks 1. Corresponding pipelines coloured as the tanks. On the photos you see the valve chests with valves. If you want to pump out regulating tank 2 port and starboard with say 100-200 liters, you probably would like to use the smaller aux. bilge/ trimpump having a capacity of 300/360 liters pr min. You open the valves for the yellow pipeline, and discharge to sea, via the boardvalve b , in this case you may read the amount discharged on the watergauges  for reg.tanks 2 port and stb marked off per 100 liters, indicated on the image below. In case you are afraid of leaving an oilslick on the surface you don`t discharge to sea, but into MBT 3 s boardvalve (dotted pipeline) on the drawing.
If you want to fill more seawater into the tanks, you don`t use the pumps but merely open the sea valve "a" and follow the volume on the water meter in the pipeline till you have the correct amount into the tanks. The regulating tanks are vented into the controlroom as can be seen on the system drawing.
The above system is used both on the surface as well as submerged.The valve are indeed used in combination, but not mechanically interconnected.The forward aft- trim is a separate system and although you use the same pumps, you have forward and aft trim tanks, the pipelinesystem is different but interconnected. Both systems can be operated by compressed air as well.
It might require some studying of the of the different systems to have a full understanding. I fully understand the difficulty to have a 100% correct understanding, but these systems are very important in a correct operation of a submarine so just ask your questions.
Tore