Tores mailbox VIIC and VIIC/41 operation and technical details

[tore]

Don.
 In the jungle of pressure definitions it is easy to get confused. The way we used the pressuregauges was generally the figures at 0 was atmospheric pressures anything below was vacuum above was pressure. So when blowing the ballasttanks by exhaust at 0.5 at. it meant 0.5 at above the atmospheric pressure. If you were using like 0,5 at absolute you would have been venting the tanks. What sometimes could be a problem was that the overpressure in the boat could be excessive and the manometersan  would show  a higher pressure  as the 0 point could be at 0.1 or 0.2 at. When exhaustblowing this would not occur. The gauge you show could very well be the exhaustback pressure gauge.
Tore

[Don Prince]

Hello Mr. Tore,


As far as exhaust pressure blowing goes, I believe I will stick with the pressure that is seen on the pressure gauge (0.5 atu = 0.5 bar)...

I was thinking (very dangerous sometime), but I never seen any indication as to the location of the hydraulic oil supply tank (over 350 Gallons).  It looks like a suitable space for that large tank would be under the helmsman and plainsmen seat???  am I close?


Regards,
Don_

[Don Prince]

Hello Mr. Tore,


One other question...  the "Fahrtmeßanlage" speed measuring system has a dial that indicates 0 - 20 Knots.  Was it sophisticated enough to take into account for the influence of the ocean current (+ or - knots)?


Regards,
Don_

[Don Prince]

Hello Mr. Tore and Maciek,


I updated Skizzenbuch with added pages 204, 205 on the oxygen system with info from Maciek, and the latest version was uploaded to dropbox (modified date Oct-21-2014)...


Regards,
Don

[SnakeDoc]

I was thinking (very dangerous sometime), but I never seen any indication as to the location of the hydraulic oil supply tank (over 350 Gallons).  It looks like a suitable space for that large tank would be under the helmsman and plainsmen seat???  am I close?

Under the plainsmen and helmsman seat is something like tool cabinet. The hydraulic oil supply tank is located behind the compressed air manifolds. I have attached drawing with its location marked. I have also attached photo with good view of the one hydraulic pump with driving motor. There are also visible pipe leading from the pump to the accumulators and pipe leading from the collecting tank (with large valve).

One other question...  the "Fahrtmeßanlage" speed measuring system has a dial that indicates 0 - 20 Knots.  Was it sophisticated enough to take into account for the influence of the ocean current (+ or - knots)?

No, the log operating on the principle of the Pitot tube measures speed relative to the surrounding water only.

--
Regards
Maciek

[SnakeDoc]

Tore, thank you for your answer.

When you operated a British submarine you got the impression of a very modern vessel whereas the VIIC was a sturdy oldfashioned full of mechanical rods and gear vessel. Yet the VIIC gave a good feeling as you had direct mechanical contact with the elements you operated.

I wonder about diving planes. They are quite crucial elements - if they are damaged (i.e. disconnected from the driving gear) or jammed (especially in "dive" position), they can easily  cause the depth excursion incident. That's why, they are equipped with some backup system - as well driving gear (manual drive) as the mechanical position indicators (apart from electric ones). I wonder, why the German designers decided to use remote mechanical drive from the control room. It would be much safer to provide emergency steering stations locally - in the forward and aft torpedo room respectively (as in the case of the main rudder). I can imagine - that due to depth charges explosions - there are some damages to the relatively long driving shaft lines possible.

As the some kind of interesting fact I can say, that larger U-Boats (type IX and XIV) were equipped with some kind of coupling gear - the both hand-wheels on the plainsmen station could be coupled together to control aft or forward diving planes from both stations - I believe, it could be used, when aft or forward diving planes were operated so hard (due to damages), that one man could not stand it. In such situation, there was additional (third) electric console provided, which was operated by another crew member, who controlled the remaining (undamaged) diving plains pair.

--
Regards
Maciek

[tore]

Don.
The log system is explained very good by Maciek, I can only add the Pitot system is based on a static and dynamic pressure, the dynamic nozzles (two) are place on port and stb bow and the static nozzles are I believe at the forward end of MBT 3.
Tore

[tore]

Don.
I have made a sketch showing the various hydraulic supply components place in the control room. Note the hydraulic tank capacity is 345 liters not gallons.
Tore

[SnakeDoc]

Hi Gents,

The log system is explained very good by Maciek, I can only add the Pitot system is based on a static and dynamic pressure, the dynamic nozzles (two) are place on port and stb bow and the static nozzles are I believe at the forward end of MBT 3.

I have attached photos of the dynamic nozzles on the bow.

Note the hydraulic tank capacity is 345 liters not gallons.

I estimate its size on approximately 110 cm length, 75 cm width and 40 cm height.

--
Regards
Maciek

[tore]

Maciek.
I believe the mechanical emergency operation of the hydroplanes was very sturdy and placed inside the pressurehull could take a lot of beating from depthcharging. However the system required a lot of maintenance (greasing) to stay relyable. A local 3 positions for operations of rudder and hydroplanes would be a challenge for the immediate communication and would require further instruments for immediate response to keep the vessels  positions (angle) which is a combination of operation of fwd. and aft hydroplanes. I guess I would have preferred to maintain the system of a VIIC above three local emergency operations.
Tore

[Don Prince]

Hello Mr. Tore and Maciek,


Thank you for the information about the location of the hydraulic system tank and the speed measuring system...  I updated Skizzenbuch and added the Hydraulic system tank location in the hydraulics section, and the speed measuring system with the rudders and hydroplanes.  The latest version of Skizzenbuch was uploaded to dropbox...


Kind regards,
Don_

[tore]

Don.
I have checked your latest additions to your Skizzenbuch and it looks OK to me. A minor comment which has nothing to do with the understanding of the system. I just accidentally stumbled over your remark in connection with the valve assembly on page 225 :" ... the valves were called a christmas tree because of the multicoloured handwheels." I have previously on this thread warned against making conclusions based on the present state of the museums U 995. The vigorous use of multi coloured items has nothing do with the original.  Today all the red paintings makes the impression that poor old U-995 got the measles.
We did not use the christmas tree expression 60- 70 years ago in Europe, I guess it came from US oil exploration and was used in the beginning as a slang for the cluster of valves on the top  of the drilling hole containing the blow out preventer. The expression reflects rather to the shape of the valve cluster having many branches and not colours as the assembly was not coloured.
Tore

[SnakeDoc]

Hi Tore,

I believe the mechanical emergency operation of the hydroplanes was very sturdy and placed inside the pressurehull could take a lot of beating from depthcharging. However the system required a lot of maintenance (greasing) to stay relyable. A local 3 positions for operations of rudder and hydroplanes would be a challenge for the immediate communication and would require further instruments for immediate response to keep the vessels  positions (angle) which is a combination of operation of fwd. and aft hydroplanes. I guess I would have preferred to maintain the system of a VIIC above three local emergency operations.

Thank you for your answer. Of course, emergency steering stations located locally in aft and forward torpedo rooms would be quite challenging.

Anyway, US Gato and Balao diving planes systems were operated hydraulically. The description can be found here:
http://www.maritime.org/doc/fleetsub/hydr/chap5.htm#5A
As I understand, there is no other way of controlling them than hydraulic. In case of failure of the hydraulic pumps, the only emergency recovery mode is the hand pump. It seems, that in case of damaging the hydraulic piping, the whole system is broken.

On the other hand, the hydraulically driven diving planes on type XXI U-Boats were fitted with emergency hand drive (but only aft pair).
I suppose, that it is because the aft plains have more effect on the control of the submarine than forward planes.

Here is another example - the British Oberon class submarine:
http://maritime.org/doc/oberon/hydraulics/index.htm#pg26

These subs have also hydraulically operated diving planes, and it seems, that after pair has the following emergency gear - in case of damage of the hydraulic system, to the actuating piston controlling the planes can be connected high pressure air, which controls the angle of planes (or sets them to the "surface" position).

--
Regards
Maciek

[tore]

Maciek.
Interesting  information on the British "O" class which at my time was very hush,hush, allthough we had a naval architect reading a paper on the development of the class. Further it gives a documentation of the extensive use of hydraulics of the British submarines compaired to the Germans. Visually an obvious difference between the British ( and US) and the German submarines during WW2 was the forward hydroplanes. The British and US submarines had the hydroplanes well above the surfaced waterline and the Germans well below. There were many pros and cons to both systems. The German having an immediate quick active effect on the diving, the British needed to be folded out and was not active before the bow was submerged. The British was easier to manoeuvre in harbour but had an extra element (folding). The German could have a problem with dropping the anchor and the anchor cable, I have personally experienced the anchor cable being stuck between the hydroplane and guard ( deflector), but the hydroplanes could act as a stabilizing instrument cruising surfaced in rough sea. To a certain extent a similar system is used as stabilizers on large passenger vessels today. I post a photo never published before showing me jumping into the sea in shallow water divingsuit close to the forward folded hydroplane of a British T class submarine.
Tore

[Don Prince]

Hello Mr. Tore,


I have a question about page 164 the second paragraph... It states the compression for blowing the ballast tanks is 1.5 atm (I believe that would be 0.5 atm plus 1.0 atmosphere external pressure  that equals 1.5 atm absolute).


Since you don't specify absolute pressure, would it be wrong to substitute 0.5 atm or atu as read on the pressure gauge in the paragraph just to be consistant?


Regards,
Don_