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I don't quite understand how an outer hull is kept from crushing since they seem to be quite thin. I'm under the impression that the gap between the outer hull and pressure hull is not pressurized at all? And it's not watertight?
 

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Interesting question. Not knowledgeable about subs, but googling around a bit, it appears the inner hull is the pressure hull, the outer is for streamlining, the gap between inner and outer holds/displaces ballast. The outer hull can be thin as it is not (much) pressurized.

No way you could get me in a sub for 6 months at a time. Much respect for the folks who serve and do.
 

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Discussion Starter · #3 ·
I come from a Navy family. Submarine men. I almost joined myself but I have a couple medical conditions that kept me out.

I should try and talk to my uncle. I rarely see him. He served on a submarine in the late 70s patrolling off the Eastern coast of Russia.
 

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Tee--

We don't go down for six months unless you're on a boomer. Fast attacks are out for six to eight weeks at a time.

AoW--

I cannot answer your question. Look up Jane's--basically the who's who of ships and war vehicles. He might detail it for you.
 

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Not sure either but, if you are correct and the gap between the two hulls is not water tight, then wouldn't the pressure in the gap simply equalize to the outside pressure?

There's a sub vet on another forum I belong to... I'll have to inquire.
 

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Not sure either but, if you are correct and the gap between the two hulls is not water tight, then wouldn't the pressure in the gap simply equalize to the outside pressure?

There's a sub vet on another forum I belong to... I'll have to inquire.
I think you'd be right if it were uncontrolled and not watertight. It sounds like they control the volume of water entering and leaving the gap (and thus the volume of air entering and leaving the gap) to help the sub sink or rise (more water = sinkage, more air = rise). With the ability to control the water in the space, it wouldn't equalize to the outside pressure.

Imagine holding a plastic bag full of air deep under water in a pool. (also imagine that the plastic bag doesn't deform when you dive deep in the pool). Then you open the bag just a bit, so half the air flows out and it's half full of water. Then you close the bag. The pressure in the bag isn't the same as the surrounding pressure. At least that's what it sounds like, but I have no actual knowledge on the subject.
 

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I posed this question to the other forum along with what I had suggested. The person who responded wasn't the sub vet I aimed it at but this was the response I got. If I get a different one later I'll post that as well...

Downtown at the Inner Harbor is the WW2 submarine USS Torsk. And that's exactly how that boat works - the gap between the pressure hull and the outer hull free-floods. The water pressure is the same on both sides of that thin skin.
We have a sub at the Carnegie Science Center here in Pittsburgh that's open for tours. I went on one a number of years ago but I don't recall if they addressed that particular question or not.

At any rate, I'm not sure if it's something they control or not. The air/water volute to control rise and fall is a function of the ballast. I know that most subs have more than one, but I'm not sure that the gap is a part of that system or not.
 

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Wiki covers it pretty well in section 3:

http://en.wikipedia.org/wiki/Submarine

Here is my understanding, kept simple. Think of the outer hull as a series of tanks against the pressure hull. They have valves at the top and bottom. On the surface the tanks are full of air and both set of valves are closed. To submerge all valves are open and the tanks fill with water. While submerged they are open to the sea so the pressure is the same as the outside. To surface they close the top valve and use compressed air to blow the water out.

Things changed some after the nuclear age. I think subs can go deep enough where the pressure is to great for air to blow the tanks, and our subs only have a tank in the nose and tail, the rest is just the pressure hull.

Don’t know how much you want to trust an accountant on this.
 

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Ok, so the sub vet on the other forum weighed in with this...

There's no pressure difference across the outer hull.

The area between the inner (pressure) hull and the outer hull is mostly the ballast tanks.
To submerge, you open vent valves on the top to let the air out and seawater floods in from the bottom.
When you want to stay surfaced, you close the vents and pump low pressure air into the ballast tanks, which pushes the seawater out the bottom.
For an emergency surface, you blow high pressure air into the ballast tanks to displace the water very quickly and hopefully regain positive buoyancy.
Hope that answered your question.
 

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I guess it would suck bad if for any reason the thin outer hull were to be compromised near the top; blub, blub, blub... Of course the designers must have planed for that and segment sections? Just like the bulkheads on the Titanic right?! (too soon? ;D)
 

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I guess it would suck bad if for any reason the thin outer hull were to be compromised near the top; blub, blub, blub... Of course the designers must have planed for that and segment sections? Just like the bulkheads on the Titanic right?! (too soon? ;D)
Yes to both. The thin outer hull is why aircraft could sink subs with machine guns so well in WWII. Somewhere online there should be a diagram showing the number of tanks.
 

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I guess it would suck bad if for any reason the thin outer hull were to be compromised near the top; blub, blub, blub... Of course the designers must have planed for that and segment sections? Just like the bulkheads on the Titanic right?! (too soon? ;D)
Well, funny you should ask because I asked him a similar question. About whether or not you can raise the sub if the hull is damaged. He responded with this...

Yes. You can "drive" the boat to the surface even if the ballast tanks are damaged (provided you don't have other damage that is making you too heavy, like flooding inside the pressure hull, or if you don't have any propulsion).

For example, this boat hit an underwater mountain while running at high speed... and made it home.
They did an emergency blow, which put enough air into the damaged (and undamaged) ballast tanks to help them get to the surface, then they ran home on the surface while constantly pumping air into the ballast tanks using both the exhaust from the diesel engine and the low pressure blower.



PS There are also some other water tanks inside the pressure hull that are filled with varying amounts of seawater to fine-tune the buoyancy and to adjust the "trim" of the boat. The "trim" is keeping the forward and aft buoyancy balanced so the ship tends to stay level if the planes are neutral.

One of the pranks experienced submariners play on new officers (with the Captain's knowledge) is called a "trim party."
During one of those the 2/3 of the crew that is not on watch get up and simultaneously all run to the bow, once the Officer of the Deck gets the boat trimmed by pumping a bunch of water aft, we all then run to the very stern. Lather, rinse, repeat, and repeat, and repeat...
Pretty cool stuff.
 

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Don't touch it or you'll get seamen all over you.
 

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I can ask my brother (former subrider) if you still want an answer for a guy who rode fast attack subs. All I remember him talking about is pinhole leaks and a guy dying because he was decapitated by one.

The 637, 688, and 688i class subs (fast attacks) are all single hulled. I was on the William H. Bates, Indianapolis, and the Santa Fe.
 

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I was a semen once but then I won!!
 
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