Duration of asdic searches?

[Fidd]

Ok, I completely buy that as an explanation which squares anecdotal evidence (accounts) with some sound physics.

Out of curiosity, does anyone know the time intervals at different depths, for the main ballast tanks to be blown or flooded?

The reason I ask is that again working from anecdotal accounts, a loss of vertical control was not that unusual, with u-boats being "blown to the surface". This suggests that in attempting to recover from great depths, the main ballast tanks were blown at least partially, but that reflooding them either not be achieved quickly enough to prevent broaching to the surface, or, that once a rapid upwards movement began, it could not be arrested despite the main ballasts being reflooded at depth.

I suspect the latter, which might indicate that the inertia of our boats is a little off, as in the ordinary way we can always (air permitting) blow the mains at depth and arrest that ascent before broaching...

It might also mean that our planes are rather too "fast-acting" in altering the pitch of the boat?

[Kermit the Frog]

Originally Posted by Fidd

The reason I ask is that again working from anecdotal accounts, a loss of vertical control was not that unusual, with u-boats being "blown to the surface". This suggests that in attempting to recover from great depths, the main ballast tanks were blown at least partially, but that reflooding them either not be achieved quickly enough to prevent broaching to the surface, or, that once a rapid upwards movement began, it could not be arrested despite the main ballasts being reflooded at depth.

True

Whole mechanism workes like these: Let's say that you pumped out 5 tons of water from forward and 5t from aft tanks at 180m depth. Your boat is slowly rising. The more you go up the smaller pressure of water around you. At 90m depth there's 10 t of water less in your tanks - air inside the tanks expands. at 45m there's allready 20 t of water pumped out. The shalower you are the faster you're surfacing. It works in game, except one thing.

the "negative tanks" is placed inside the pressure hull. The other 4 are not. They're not pressure - resist. That means, if you blown your balast at 200m depth you have to keep inside and outside pressure at the same level. If they're full of air it must stay like these till surface. Otherwise if you open valves at let's say 100m the water surrounding will crusch them. It worked like these in real U-Boat. I am not sure about the game

[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.