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Catfish · 08-09-16, 09:07 AM

^ I'd come with your time machine, but minus the depth charges please

"Untertriebszellen" would be something like negative buoyancy cells, maybe to break the surface energy (but i doubt this plays a major role), but in any case to minimise the diving time.

Afaik a usual VII type boat had two of those, located near (left and right of the ballast tank 3, or main ballast tank) the control room, at the center of gravity of the boat. They were operated together, though Werner in his "Iron coffins" speaks about flooding the "fore part" only(?), to increase the diving angle faster in case of a dive. This may be wrong though, Werner's book is more of a novel than a real report, and has been criticized for a lot of wrong technical descriptions. The man "Werner" seems to have never existed, though the man using this pseudonym knew "a bit" about U-boats.

As soon as the U.-cells are flooded, the boat is running with closed upper venting valves, to be able to blow them asap after diving. In case they cannot be blown immediately after the sail submerging, the boat is in danger to "fall through" and get too deep, out of control.

From the "Tauchvorschrift für Unterseeboote":

Untertriebszellen

131. Bei Booten mit Untertriebszellen wird wie folgt verfahren: Die Untertriebszellen werden, wenn das Boot alarmtauchklar ist, über Wasser gefüllt gefahren, so daß dem Boot ein der Größe der Zellen entsprechender Untertrieb gegeben ist. Nach der Ausführung des Befehls „Fluten“ und merklicher Falltendenz werden die Untertriebszellen auf den Befehl des L.I. „Ausdrücken“ ausgedrückt.

(131. If the boat has negative buoyancy cells, the procedures are as follows: The U.-cells are being flooded when the boat is running surfaced, and in "ready to submerge" state (edit: alarmtauchklar=all men at diving positions, boat prepared for emergency dive - so .. usual condition in enemy waters), so that there is an appropriate negative buoyancy. After execution of the order "Fluten" (edit: flood the tanks!) and a perceptible tendency of falling, the cells are being blown out by order of the LI (Leitender Ingenieur).

Der beste Zeitpunkt des Ausdrückens für mittlere Boote ist eine Tiefe von etwa 8 bis 10 m, für große Boote eine Tiefe von 10 bis 12 m. Erfahrungsgemäß beruht die Wirkung der Untertriebszellen in erster Linie im schnelleren Durchbrechen durch die Wasseroberfläche beim Tauchen. Da die schnelle Erreichung großer Tiefen fast ausschließlich von der Lastigkeit und der Fahrtstufe abhängig ist (etwa 25 bis 30°, 2 x G.F.), ist es falsch, die Untertriebszellen auf größerer Tiefe auszudrücken, da der äußerst geringe Vorteil in keinem Verhältnis zu der Gefahr steht, in die das Boot in einem solchen Falle geraten kann. Insbesondere steigen der Luftverbrauch und die Ausdrückdauer ganz erheblich.

(The best time for the blowing ballast of boats of middle size is a depth of 8-10 meters, for big boats a depth of 10-12 meters.
From experience the essential effect of the U.-cells is one of breaking through the water surface during a dive. Because the reaching of greater depths is almost entirely dependent of angle and speed (ca. 25 to 30°, 2x all ahead) it is wrong to blow them out at greater depth, because the advantage would not be in due proportion to the danger, the boat will be in. Especially wastage of air and the time of the blowing ballast increase badly.)

132. L.I.: „Ausdrücken“.

Daraufhin wird das Ventil „Ausdrücken Untertriebszellen“ aufgerissen und mit höchstmöglichem Druck (20 bis 30 at) ausgedrückt. [...]

(132. LI: "Blow ballast".
With this order the "Blow U.-cell" valve will be torn open, and be blown out by the utmost pressure (20-30 at). [...]

The general procedure was to have the U.-cells being fully blown at 19 meters of depth.

From the plan you posted you can see the the one big main air induction tube coming from the conning tower and ending at the centered valve in the engine room above our heads, which had to be closed when diving. The two smaller wheels near it at the sides were for the closing/opening of the two exhausts, which had to be thoroughly maintaind for closing properly. Diesel exhausts and carbon used to build up on the valve surfaces, so they had to be sanded and polished regularly. I guess we spoke about that too, but..

All the best,
CF

08-09-16, 09:07 AM	#92
Catfish Dipped Squirrel Operative Join Date: Sep 2001 Location: ..where the ocean meets the sky Posts: 16,897 Downloads: 38 Uploads: 0	^ I'd come with your time machine, but minus the depth charges please "Untertriebszellen" would be something like negative buoyancy cells, maybe to break the surface energy (but i doubt this plays a major role), but in any case to minimise the diving time. Afaik a usual VII type boat had two of those, located near (left and right of the ballast tank 3, or main ballast tank) the control room, at the center of gravity of the boat. They were operated together, though Werner in his "Iron coffins" speaks about flooding the "fore part" only(?), to increase the diving angle faster in case of a dive. This may be wrong though, Werner's book is more of a novel than a real report, and has been criticized for a lot of wrong technical descriptions. The man "Werner" seems to have never existed, though the man using this pseudonym knew "a bit" about U-boats. As soon as the U.-cells are flooded, the boat is running with closed upper venting valves, to be able to blow them asap after diving. In case they cannot be blown immediately after the sail submerging, the boat is in danger to "fall through" and get too deep, out of control. From the "Tauchvorschrift für Unterseeboote": Untertriebszellen 131. Bei Booten mit Untertriebszellen wird wie folgt verfahren: Die Untertriebszellen werden, wenn das Boot alarmtauchklar ist, über Wasser gefüllt gefahren, so daß dem Boot ein der Größe der Zellen entsprechender Untertrieb gegeben ist. Nach der Ausführung des Befehls „Fluten“ und merklicher Falltendenz werden die Untertriebszellen auf den Befehl des L.I. „Ausdrücken“ ausgedrückt. (131. If the boat has negative buoyancy cells, the procedures are as follows: The U.-cells are being flooded when the boat is running surfaced, and in "ready to submerge" state (edit: alarmtauchklar=all men at diving positions, boat prepared for emergency dive - so .. usual condition in enemy waters), so that there is an appropriate negative buoyancy. After execution of the order "Fluten" (edit: flood the tanks!) and a perceptible tendency of falling, the cells are being blown out by order of the LI (Leitender Ingenieur). Der beste Zeitpunkt des Ausdrückens für mittlere Boote ist eine Tiefe von etwa 8 bis 10 m, für große Boote eine Tiefe von 10 bis 12 m. Erfahrungsgemäß beruht die Wirkung der Untertriebszellen in erster Linie im schnelleren Durchbrechen durch die Wasseroberfläche beim Tauchen. Da die schnelle Erreichung großer Tiefen fast ausschließlich von der Lastigkeit und der Fahrtstufe abhängig ist (etwa 25 bis 30°, 2 x G.F.), ist es falsch, die Untertriebszellen auf größerer Tiefe auszudrücken, da der äußerst geringe Vorteil in keinem Verhältnis zu der Gefahr steht, in die das Boot in einem solchen Falle geraten kann. Insbesondere steigen der Luftverbrauch und die Ausdrückdauer ganz erheblich. (The best time for the blowing ballast of boats of middle size is a depth of 8-10 meters, for big boats a depth of 10-12 meters. From experience the essential effect of the U.-cells is one of breaking through the water surface during a dive. Because the reaching of greater depths is almost entirely dependent of angle and speed (ca. 25 to 30°, 2x all ahead) it is wrong to blow them out at greater depth, because the advantage would not be in due proportion to the danger, the boat will be in. Especially wastage of air and the time of the blowing ballast increase badly.) 132. L.I.: „Ausdrücken“. Daraufhin wird das Ventil „Ausdrücken Untertriebszellen“ aufgerissen und mit höchstmöglichem Druck (20 bis 30 at) ausgedrückt. [...] (132. LI: "Blow ballast". With this order the "Blow U.-cell" valve will be torn open, and be blown out by the utmost pressure (20-30 at). [...] The general procedure was to have the U.-cells being fully blown at 19 meters of depth. From the plan you posted you can see the the one big main air induction tube coming from the conning tower and ending at the centered valve in the engine room above our heads, which had to be closed when diving. The two smaller wheels near it at the sides were for the closing/opening of the two exhausts, which had to be thoroughly maintaind for closing properly. Diesel exhausts and carbon used to build up on the valve surfaces, so they had to be sanded and polished regularly. I guess we spoke about that too, but.. All the best, CF __________________ >^..^<*)))>{ All generalizations are wrong.