Quote:
Originally Posted by ABBAFAN
I meant as a way of slowing the ascent or even to prevent it from speeding up as more and more balast is expelled by the expanding air already in the tanks.
Perhaps similar to rising and descending in a gas balloon?
On the other hand, would decreasing water density compensate anyway by reducig the boat's bouyancy as she rises?
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Well in a hot air balloon lift is generated by the hot air in the balloon itself. As the air cools it descends thus making it necessary to heat the air trapped within the balloon to maintain altitude or to ascend. That's pretty well know.
A submarine operates on a completely different principle. When it submerges it takes on water in its ballast tanks to maintain a state of neutral buoyancy. Depth changes are accomplished by the use of the control planes. Once submerged the main ballast tanks aren't touched except to surface the boat. There's no need to blow water out or take water on except for when your displacement would change (consuming food stores, firing torpedoes, etc) and there is an auxiliary system for this purpose.
As for your second question about water density affecting buoyancy, I'll hold off on answering that for now.