Duration of asdic searches?

[Fidd]

That doesn't quite make sense to me yet. If you've blown the main ballast tanks (hence-forwards MBT's) at 200m, then the air pressure inside is circa 20 atmosphere's, however, by the time you reach the surface you've still got 20 bar in the MBT's, but nil outside water pressure.

So unless you've vented that high-pressure air in the MBT's during the ascent, you've now an air-pressure being exerted on the inside of the MBT's of 19 bar, or 266lbs per square inch.

That's an awful lot! So either the MBT's were resistive to pressures of that order, or, there was a means to relieve climbing air-pressure within the MBT's as the U-boat ascended?

[Kermit the Frog]

Originally Posted by Fidd

That doesn't quite make sense to me yet. If you've blown the main ballast tanks (hence-forwards MBT's) at 200m, then the air pressure inside is circa 20 atmosphere's, however, by the time you reach the surface you've still got 20 bar in the MBT's, but nil outside water pressure.

So unless you've vented that high-pressure air in the MBT's during the ascent, you've now an air-pressure being exerted on the inside of the MBT's of 19 bar, or 266lbs per square inch.

That's an awful lot! So either the MBT's were resistive to pressures of that order, or, there was a means to relieve climbing air-pressure within the MBT's as the U-boat ascended?

Main Balast tank works different - it is pressure tight. other tanks are not. If pressure around tanks drops down - air inside expands and water from the tanks is "pushed out"

To be correct: Main Balast Tank (the Negative) is placed inside the pressure hull. The forward and aft balast tanks are placed outside of the hull. As far as i know they were constatntly opened from below. That is why you just need to open top vents to dive the submarine. To survive U-Boat need only MBT. All external balast tanks can be destroyed and u-boat is still abble to float.