Quote:
Originally Posted by sober
I only use the negative tank and dive planes for depth control
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In reality they had so called trimming and adjusting tanks ("Regelzellen" in German) which were used to compensate for weight changes due to food and fuel-consumption, torpedoes etc. Thatīs why they had to "balance and Level" the boat every day. The negative tank (German: Untertriebszelle) was just there to speed up diving. It was blown (=emptied) fairly quickly after diving.
Physically interesting fact: When they went Deep, they FILLED the negative tank a little bit to KEEP the U-Boat ballanced. The reason for this: the deeper a Sub dives, the more it is "squeezed" so it loses volume. Less volume means less water replacement. This will Change the raise-sink tendency. So they had to make the boat heavier in great depths to compensate for that.
Another effect, which has similar physics: in very calm weather they could "hang" the U-Boat at periscope Depth without engines (=fully stopped). Certainly, a ZERO balance is not possible, but the periscope shaft itself changed the U-Boatīs replacement when it went a bit deeper or raised a bit, so this tiny little bit was enough to "keep" the Sub stable at periscope Depth if it was really well balanced by the L.I.
Quote from the novel "Das Boot" (losely translated): "You see, thereīs a lot of physics and chemistry going to sea with a U-Boat!"