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Old 12-09-2006, 07:51 AM
astro is offline
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Question about Submarine Torpedo Tubes and Firing Systems


I was reading this article and didn't understand this part.

Quote:
With the nuclear SMs the deep discharge problem was beyond the capabilities of high pressure air systems and a method of discharging the torpedo using the output of a high-pressure seawater pump was perfected by the Americans. This could be used at any depth that the boat was capable of. And that's how it's done today.
What is the "deep discharge" problem?
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Old 12-09-2006, 08:27 AM
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Pressure of the seawater is higher than achievable with the air compressors, so the air remains compressed on discharge instead of expanding and ejecting the torpedo?
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Old 12-09-2006, 08:39 AM
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WAG-An air ejection system would need to provide about 900 psi just to balance outside water pressure. In addition whatever differential pressure is required for ejection in order to fire a torpedo at 2000 ft. depth must be added to that.

An on-board water pump only has to supply the differential pressure..
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Old 12-09-2006, 08:40 AM
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Torpedoes are (mostly) fired by shooting the out with compressed air. If you are deep, it takes several acre-feet of compressed air to fire even one. You had best come up higher before you shoot, or you will use a lot of your breathing air.

Using water to shoot the fish out of the tube solves that. This is called 'swimout.' It seems to be harder to do than it looks, but has the added advantage of greater silence. Or so I am told.
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Old 12-09-2006, 08:41 AM
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Ooops. The 900 psi is for firing at a depth of 2000 ft.
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Old 12-09-2006, 08:55 AM
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Quote:
Originally Posted by Paul in Saudi
... you will use a lot of your breathing air.
According to the cite, the firing air was stored on board in air bottles. I seem to recall that this used to be a problem with diesel-electric sub. They fired from periscope depths because the periscope was needed for aiming. In order to avoid release of a large bubble of air which would give away the sub's location on firing they "swallowed" most of it back into the boat. So after a period of heavy firing they needed to surface in order to depressurize the sub.

The cite also implies that firing a torpedo is quite an operation. Submarines are quite sensitive to trim and all of the letting in seawater and then ejecting both it and the torpedo seems to involve a fairly complex operation in order to maintain the boat's trim and avoid a sudden deep dive or inadvertent surfacing. I can see how this wouldn't be all that serious on a 5000 ton nuclear, but for the diesel-electrics it could be.
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Old 12-09-2006, 11:20 AM
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Quote:
Originally Posted by David Simmons
The cite also implies that firing a torpedo is quite an operation. Submarines are quite sensitive to trim and all of the letting in seawater and then ejecting both it and the torpedo seems to involve a fairly complex operation in order to maintain the boat's trim and avoid a sudden deep dive or inadvertent surfacing. I can see how this wouldn't be all that serious on a 5000 ton nuclear, but for the diesel-electrics it could be.
I took a tour of a Los Angeles-class submarine with some folks I work with, and one of the most important jobs in the control room is keeping the submarine at the right tilt (usually no tilt). The chief who was showing us the controls mentioned that at a shift change, he would notice the boat beginning to tilt as the sailors in their racks woke up and headed towards the other end of the submarine to relieve the sailor at their station. Torpedoes are much heavier than sailors, so getting rid of one up front would definitely cause the boat to lean backward a little.
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Old 12-09-2006, 09:27 PM
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Former Los Angeles-class (688-I) submarine officer here...

Modern U.S. torpedoes are launched by a high-pressure compressed air system (3,000 psi) acting on a ram that pressurizes a tank of seawater that surrounds the aft end of the torpedo tube. This tank is unimaginatively called the water-round-torpedo (WRT) tank, and is connected to the tube by a set of louvers, which are opened when the weapon is launched.

And as Jurph noted, it is a concern of the ship control party to maintain the trim of the boat when launching a nearly two-ton weapon from so far up forward. This is somewhat offset however, by the flooding of the tube after the weapon leaves the tube. (This water is subsequently drained into a tank.)
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Old 12-10-2006, 11:19 AM
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Quote:
Originally Posted by robby
... a high-pressure compressed air system (3,000 psi)
Corresponding to a depth of about 6500 ft.
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Old 12-10-2006, 11:57 AM
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Quote:
Originally Posted by David Simmons
Corresponding to a depth of about 6500 ft.
So it'd be able to launch torpedos at any depth it can safely dive to.
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Old 12-10-2006, 12:05 PM
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Quote:
Originally Posted by Crescend
So it'd be able to launch torpedos at any depth it can safely dive to.
Well, there needs to be some some differential between the pressure behind the ram and the ambient sea water pressure. The actual maximum launch depth would be some unknown amount less than the cited number.

But yes, they can launch from any pretty deep depth.

And I have no special knowledge but I think I'll drop this since it's probably a sort of sensitive area.
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Old 12-10-2006, 02:54 PM
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Quote:
Originally Posted by David Simmons
Well, there needs to be some some differential between the pressure behind the ram and the ambient sea water pressure. The actual maximum launch depth would be some unknown amount less than the cited number.

But yes, they can launch from any pretty deep depth.

And I have no special knowledge but I think I'll drop this since it's probably a sort of sensitive area.
Mostly it is a bit kindergarten, flood the tube and give it a puff of air to get it on its way.

Logical.

But what is interesting is the 3D guidance system, few targets have hulls that are 6000ft deep. It has to be some sort of passive magnetic homing device, probably triggered at a depth or distance well outside the domain of momma.

The concept of a sub torpedoing itself is both comical and .. well disturbing.
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Old 12-10-2006, 03:11 PM
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Quote:
Originally Posted by FRDE
The concept of a sub torpedoing itself is both comical and .. well disturbing.
It has happened
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Old 12-10-2006, 04:01 PM
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Quote:
Originally Posted by Rick
It has happened
As far as I know, this is the only incident for which we have reliable documentation. Some other submarine sinkings have been attributed to "self-torpedoing". Divers off the Eastern US coast discovered a German submarine that had been sunk by explosion. No action report claimed it, and historians surmise that it accidentally sank itself.

BTW, this scenario also happens in the movie version of Hunt for Red October. I don't remember if it's the same way in the book.
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