a question on VII depths

Schroeder · 06-21-09, 08:43 AM

Quote:

Originally Posted by Letum

No, not iron coffins.
I strongly suspect I must have read something about U-175, but I can't think which book!

The U-boat archive describes what I read well:

http://www.uboatarchive.net/U-175INT.htm

It is odd that a sub with a broken pressure hull should be able to go that deep.

Letum · 06-21-09, 10:38 AM

Would it not be even stranger if it went to such depths undamaged?

Schroeder · 06-21-09, 12:36 PM

Sure, but I wonder that a breached pressure hull could withstand that enormous depth. I mean imagine how deep an undamaged sub should be able to go if a damaged one can reach ca. 275m.
Sounds a bit odd to me.

john doie · 08-19-09, 06:03 AM

Correct me please, 'cause I have been living under Hollywood special efects for a while, but a submarine doesn't behave as an aicraft. A fracture in the pressure hull is not instantly fatal. It's seriousness depends on depth, on metal strenght and placement. Water would be forced in at great pressure, but it is a fissure in the metal skin. With time, pressure and water, it will grow bigger, but if water is pumped out of the boat as fast as it gets in, and if the boat is brought to a safe depth, it will survive.

This will illustrate what I mean>

Schroeder · 08-19-09, 06:17 AM

Yes, but what happens if you apply pressure with a pencil on a piece of clothes for example? it can withstand the pressure for some time but if it grows too strong it will be pierced and then your pencil can open the hole easily. The same happens with a pressure hull. If it is intact it can take a lot of pressure but if there is a hole in it the area around the hole will become pretty weak and give way. (at least that's what I'm thinking but maybe someone here has better knowledge of that)

john doie · 08-19-09, 07:07 AM

Yes, it gives way, but not in a second. It takes time. It is related to the internal structure of the metal that makes the pressure hull. A fault in the metal can doom a submarine. Pressure does the rest. It also depends how much pressure is applied, and for how long. Too much pressure, like 300+m depth will work faster then 210m depth.

What I am trying to say is that pressure is forcing water in and pushes against the pressure hull. In order for the hull to fail, it needs to fail at resisting the push from pressure, not at failing to prevent water from comming in (with the mention that water comming in has to be equal or lower with water pumped out). So this bring us to the point where that crack causes a fail in the pressure hull. If it doesn't, all is ok ... for the moment.

Look at this. The beam first bends, then cracks, and lastly fails. It takes aditional pressure before a weakened structure fails. Same is on pressure hulls.

Melonfish · 08-19-09, 08:30 AM

i'm sure they touch on this in Das Boot too (the book) about the fact that they didn't open a valve so kept flooding the tanks and whatnot thinking they weren't leaving the surface?

as for crush depths i've never been deep enough to get smushed except once when i flooded heavily and ended up on the bottom trying to repair frantically.
3 blows of compressed air later and alot of pumping and we slowly started to rise again.

06-21-09, 10:38 AM	#2
Letum Navy Seal Join Date: Feb 2005 Location: York - UK Posts: 6,079 Downloads: 43 Uploads: 0	Would it not be even stranger if it went to such depths undamaged? __________________

06-21-09, 12:36 PM	#3
Schroeder Navy Seal Join Date: Apr 2008 Location: Banana Republic of Germany Posts: 6,170 Downloads: 62 Uploads: 0	Sure, but I wonder that a breached pressure hull could withstand that enormous depth. I mean imagine how deep an undamaged sub should be able to go if a damaged one can reach ca. 275m. Sounds a bit odd to me. __________________ Putting Germ back into Germany.

08-19-09, 06:17 AM	#5
Schroeder Navy Seal Join Date: Apr 2008 Location: Banana Republic of Germany Posts: 6,170 Downloads: 62 Uploads: 0	Yes, but what happens if you apply pressure with a pencil on a piece of clothes for example? it can withstand the pressure for some time but if it grows too strong it will be pierced and then your pencil can open the hole easily. The same happens with a pressure hull. If it is intact it can take a lot of pressure but if there is a hole in it the area around the hole will become pretty weak and give way. (at least that's what I'm thinking but maybe someone here has better knowledge of that) __________________ Putting Germ back into Germany.

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08-19-09, 06:03 AM	#4
john doie Nub Join Date: Mar 2008 Posts: 4 Downloads: 23 Uploads: 0	Correct me please, 'cause I have been living under Hollywood special efects for a while, but a submarine doesn't behave as an aicraft. A fracture in the pressure hull is not instantly fatal. It's seriousness depends on depth, on metal strenght and placement. Water would be forced in at great pressure, but it is a fissure in the metal skin. With time, pressure and water, it will grow bigger, but if water is pumped out of the boat as fast as it gets in, and if the boat is brought to a safe depth, it will survive. This will illustrate what I mean>

08-19-09, 07:07 AM	#6
john doie Nub Join Date: Mar 2008 Posts: 4 Downloads: 23 Uploads: 0	Yes, it gives way, but not in a second. It takes time. It is related to the internal structure of the metal that makes the pressure hull. A fault in the metal can doom a submarine. Pressure does the rest. It also depends how much pressure is applied, and for how long. Too much pressure, like 300+m depth will work faster then 210m depth. What I am trying to say is that pressure is forcing water in and pushes against the pressure hull. In order for the hull to fail, it needs to fail at resisting the push from pressure, not at failing to prevent water from comming in (with the mention that water comming in has to be equal or lower with water pumped out). So this bring us to the point where that crack causes a fail in the pressure hull. If it doesn't, all is ok ... for the moment. Look at this. The beam first bends, then cracks, and lastly fails. It takes aditional pressure before a weakened structure fails. Same is on pressure hulls.

08-19-09, 08:30 AM	#7
Melonfish XO Join Date: Nov 2006 Location: Warrington, UK Posts: 417 Downloads: 106 Uploads: 0	i'm sure they touch on this in Das Boot too (the book) about the fact that they didn't open a valve so kept flooding the tanks and whatnot thinking they weren't leaving the surface? as for crush depths i've never been deep enough to get smushed except once when i flooded heavily and ended up on the bottom trying to repair frantically. 3 blows of compressed air later and alot of pumping and we slowly started to rise again.