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Ok, so the 1 ton in the text is a suggestion for suitable positive buoyancy, not the amount of water that should be pumped because of hull contraction when diving from, say, persicope depth to 200 meters?
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Yes
. Regarding how much volume reduction the hull will suffer at X depth, this is something I haven't yet found figures of. Perhaps we could ask in the other thread that Reallydedpoet hinted at. In any case, it's hard to imagine that it can be very much. Existing yes, very noticeable, I don't think so.
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Dynamically means to maintain positive buoyancy and to steer with the rudders against this buoyancy to get a stationary balance. This also works the other way round. So, whether the boat sinks or rises when out of batteries and CA only depends on the current status of buoyancy.
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Exactly. As we know, boats were trimmed positive as a general rule, and kept at desired depth via dive planes (Which will only work >2 knots). However, when they dove deeper, leaks started appearing, hull compressed, etc, and the end result was that sometimes even negative buoyancy appeared. The 1 ton figure indicated by BDU tells us that, unless damage from depth charges and heavy leaks appear, 1 ton aditional weight via leaks would take quite a long time to build up, so it was deemed as a safe figure to ensure quick operational status to resurface and resume the engagement, instead of having to resort to the much longer and energy (Battery) consuming procedure of raising the boat via dive planes only and against the negative buoyancy.
BTW, actually and to complicate things even a bit more, the perfect buoyancy model should take into account that the higher the difference between neutral and current buoyancy for a given depth & weight (Read: water that had leaked in) the higher the forward speed you need for the dive planes to actually lift (Or sink) the uboat. There were no doubt times when using the noisy pumps to throw out the leaking water would be less bad than having to use flank speed to allow the planes to actually generate enough lift to raise the uboat with the aditional weight of the leaked water -thus exhausting the battery much quicker than with the pumps
