Tores mailbox VIIC and VIIC/41 operation and technical details

[tore]

Maciek.
Right you are Maciek, I forgot that one.
Tore

[VIC20]

great, thanks Tore and Maciek

[VIC20]

Tore, at Trim A (no oil in MBTs)…


how much water was usually the trim cells when surfaced and when submerging?
Currently in my simulation it looks like there should be at least water in the aft trim cell to trim the boat when submerged.



…and how much water was in the regulating cells for the torpedoes at the beginning? (if no torpedo was used) does it carry water for the flooding of the tubes? or where the tubes already flooded?

[Don Prince]

Thanks Mr, Tore and Maciek...


Hi Maciek,


Since they were using electric space heaters to keep warm in cold weather, does that mean at least one e-motor was running as a generator to keep the batteries topped?


Regards,
Don_

[tore]

Don.
Charging batteries was normally not depending upon the electric consumption, the condition of the batteries was the ruling factor. Twice a day the battery cells were checked for voltage, acid specific weight and temperatures. Normally we started charging when the values dropped below a limit. If however if circumstances were such that  fully charged batteries would be required, this was overruling the ideal charging.
A constant top charging would increase the risk for "gassing" eg. producing explosive hydrogengasses as well as batteries becoming "tardy". In order to keep the batteries in top shape we "drained" the batteries to the bottom once a month by running the E-motors alongside and starting charging immediately when the batteries were drained.
Tore

[tore]

Mark.
Trimming tanks.
I don`t remember we had any specific rules how much and sorry I can`t remember the forward and aft draugth. The procedure was to take a rough calculation then  balancing dive to check the calculation and sometimes it could be wrong. Then by the regulating tanks ( we never used same as f.oil bunkertanks) find an optimal trim and by adjusting the trimtanks say half full or less. The exact amount of regulatingwater would vary almost all the time depending upon consumptions as fuel, provision, freshwater etc. As the moment arm for the pitch was very long you needed only to move small amount of water to compensate for the trim f.i, as I have mentioned before, when diving station was ordered the movement of people from the 3 watch system to divingstation would require 400 liters to be pumped (yes we pumped) from aft to forward.
I leave your torpedo questions to Maciek he is more conversant with this topic than me.
Tore

[Don Prince]

Hello Mr. Tore,


I have a question about a blower vent...  I have drawn a rendition of the vent that might work.  However, the way they have drawn it on Plate 19, it looks like one blower will feed the other one and very little air would go out the vents???


Am I all wrong headed again?


Regards,
Don_

[tore]

Don.
I believe you have misunderstood the selectorsymbol. As you know on the VIICs , not equipped with schnorchel, you have two ventilation airducts one for intake the other exhaust, both operated from the controlroom and having airducts outside the pressurehull to the engineroom where they enter the pressurehull via a hullvalve with drain. I have made a sketch below showing the system green is intake and yellow exhaust. The ventilation situation you are referring to is both ventilatorfans operating in parallel which mean they have common inlet suction ( green) and exhaust (yellow). The fan selectorvalve select the suction from a number of alternatives and consist of two valves a circular selector slidevalve and a hull inletvalve.Likewise the exhaust selector slidevalve has a number of alternative positions as well as a hull exhaustvalve in one unit. If you study the sketches and photo I guess you shall have a better understanding. Remember there are many other valves in the ventilatingsystem which should be operated to get the alternative required not just the slide selectorvalve.
tore

[SnakeDoc]

Hi Gentlemen,

…and how much water was in the regulating cells for the torpedoes at the beginning? (if no torpedo was used) does it carry water for the flooding of the tubes? or where the tubes already flooded?

Well, from my studies of this topic (as no descriptions or manuals are available) I think, that torpedo compensating tanks (Torpedozelle) initially contained amount of water sufficient to flood tubes with torpedoes within them (that is about 370 litres per tube, that means that Torpedozelle 1 - aft - contained 370 litres of total 2350 litres volume and Torpedozelle 2 and 3 contained 740 litres of total 5750 litres each).
I think, that tubes were flooded from compensating tanks because in such case, the weight of boat did not change, and the trim changed only slightly.
When the torpedo was launched, the tube was fully flooded with overboard water (through the muzzle door). After closing the muzzle door, the tube was drained to the torpedo compensating tank (1680 litres of water).

Torpedozellen were also used as the aid to trim the boat, when some of the torpedoes were disposed.

And small interesting fact - aft torpedo compensating tank and one of forward compensating tanks could be used as storage tanks for wash water - they were fitted with piping to the wash water installation.
In middle period of war, forward tank was also used as fuel oil storage tank - to extend the operational range of the boat.
The U458 KTB says, that when the boat stayed in Saint Nazaire between first and second patrol (that means between 27 August - 1 October 1942), one forward torpedo compensating tank was modified to storage fuel. The additional 5,75 m³ of fuel extended patrol by two days (at 10 knots, both diesels 275 RPM).

--
Regards
Maciek

[tore]

Mark
Re Maciek post on torpedoinstallation.
It is astonishing to see how the germans used all opportunities to extend the patrols only by a few days. I made a calculation on having both fuel oil bunker and regulating tanks 1  filled with fuel, both tanks together would extend the running of the two diesels at max continuous load by some 20 hours. Otherwise thanks to Maciek I learned something new about the alternative use of the torpedo installation. I have mentioned previously our contribution to alternative use, ejecting garbage through the torpedo tubes on very long submerged schnorchling patrols. This happened to much dismay from the torpedopeople.
Tore

[VIC20]

Thanks again… btw Tore it would be interesting to see an example how you calculated things aboard. I guess you had rules of thumb to speed things up?

[tore]

Mark.
Contrary to the Germans, our EO. task was not involving trim calculations, that was No.1`s job, so I don`t remember exactly. We used as you say rule of the thumb in addition to tables and graphs I would believe, not much calculation. A testdive was the most important thing, that would reveal any mistakes and could be corrected by experience. But in order to prevent too much excitement you should be somewhat close to the correct figures. I must confess however we sometimes had excitement.
Tore

[VIC20]

Thanks Tore, I still have some question about the flooding & drainage installation:
- The water inlet, I guess it worked with the natural water pressure and you don't need the pump at all to flood the regulating tanks right?
- Is the diameter of the (water) pipes of the flooding & drainage installation identical to the ones used to blow out the tanks with compressed air?

[Don Prince]

Hello Mr. Tore,


On Plate 18 - There are 3 Air Conditioning Units on the intake / suction lines...  Were those just evaporation units? They simply ran water across a filter and interior air was then drawn through the filter.  The water evaporation and chilled the air and it was then distributed throughout the U-Boat....  Although, that would increase the humidity, so I'm not sure about the evap unit???


I seen the evap units used in many locations in the High Desert State of Arizona where my brother lives.  It is very dry and arid, so evap units work.  However, if the humidity gets above 35 percent, then evap units don't work so well...

A/C back in the 40's and 50's were quite large and required Freon gas....


Also, My DVD/CD of U-995 does not seem to have good photos of the hand-wheel with the Slide Selector lever above it.  Do you have some good photos?  There are 2 units, one for the Port blower and one for the Starboard blower correct?


Regards.
Don_

[SnakeDoc]

Don,

On Plate 18 - There are 3 Air Conditioning Units on the intake / suction lines...  Were those just evaporation units? They simply ran water across a filter and interior air was then drawn through the filter.  The water evaporation and chilled the air and it was then distributed throughout the U-Boat....  Although, that would increase the humidity, so I'm not sure about the evap unit???

The translation is quite misleading - these three units are the carbon dioxide absorbents. The units in the control room and forward torpedo room are visible on these photos:




--
Regards
Maciek