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  #1  
Old 07-20-2011, 11:53 AM
Cabin_Fever Cabin_Fever is offline
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Nuclear Submarines - Thermal Signature?

I didn't want to hijack this thread so I thought I would present this question on its own.

The topic was submarines getting stuck in ice, and a few posters mentioned using the waste heat from the reactor to melt the ice if they became stuck.

Now, from my laymans knowledge, I realize that subs are all about stealth.
Specialized propellers to reduce cavitation, the shape and configuration of the bow and other hull parts, etc.

So my question is about the reactor.
They generate heat. Apparently lots of heat.
How do they manage this heat and not advertise themselves to anyone with their heat signature?
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  #2  
Old 07-20-2011, 12:19 PM
Whack-a-Mole Whack-a-Mole is offline
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The link in the following quote contains a bunch of science if you are interested. I'll just quote the upshot:

Quote:
If the submarine were traveling on or near the surface, the surface radiation from
the water heated by the submarine might leave a thermal wake which might be
detectable. However, detecting thermal radiation directly from the submarine at a
depth greater than a few meters would be very difficult if not impossible and
submarines usually travel at much greater depths.

SOURCE: http://www.madsci.org/posts/archives...0201.Ph.r.html
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  #3  
Old 07-20-2011, 12:42 PM
Cabin_Fever Cabin_Fever is offline
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An interesting read.
So if I glean correctly, they do dump their waste heat into the surrounding water. It's just that it is virtually undetectable at depth.

Quote:
"After the invention of powerful blue - green lasers during the 1960s there has
been a great deal of research in using LIDAR (laser radar) to detect submarines
at depth; however, information about how well this works is not pubically (sic) available."
I guess we (the general public) won't really know what advanced detection systems are in use today.

Last edited by Cabin_Fever; 07-20-2011 at 12:43 PM.. Reason: spelling
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  #4  
Old 07-20-2011, 12:56 PM
Great Antibob Great Antibob is offline
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Quote:
Originally Posted by Cabin_Fever View Post
An interesting read.
So if I glean correctly, they do dump their waste heat into the surrounding water. It's just that it is virtually undetectable at depth.
Pretty much. On the surface, you'd be trying to detect the heat that leaks to the air - not the water. The heat energy is not nearly as attenuated (weakened) in air as in water.

Even a couple meters down, you'd still be trying to detect it from what it sends straight up towards the air, rather than into the water.

Think about setting a very hot pan on a block of wood. Sure, the wood under the pan might char and burn, but how much is the rest of that block heated? It's sort of the same principle.

Or even those infrared scanners they have at science museums. If you happen to wear glasses, they block your body's heat signature. Water just happens to be pretty effective at the same thing.
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  #5  
Old 07-20-2011, 01:18 PM
Cabin_Fever Cabin_Fever is offline
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Okay. I don't doubt the accuracy of these statements.
I just can't fathom (hehe, pun not intended) how dumping 100 degree C water into cooler surroundings can't be detected.
What am I missing here?
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  #6  
Old 07-20-2011, 01:29 PM
running coach running coach is offline
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Quote:
Originally Posted by Cabin_Fever View Post
Okay. I don't doubt the accuracy of these statements.
I just can't fathom (hehe, pun not intended) how dumping 100 degree C water into cooler surroundings can't be detected.
What am I missing here?
The sheer volume of surrounding water.
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  #7  
Old 07-20-2011, 01:39 PM
Machine Elf Machine Elf is online now
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Quote:
Originally Posted by Cabin_Fever View Post
Okay. I don't doubt the accuracy of these statements.
I just can't fathom (hehe, pun not intended) how dumping 100 degree C water into cooler surroundings can't be detected.
What am I missing here?
Whack-a-Mole's cite provides the technical detail without explaining, in explicit terms, the fact that water absorbs infrared radiation very well,* so your IR camera won't be able to see that warm water unless the camera is airborne and the warm water is practically on the surface, meaning there's little or no cold water between the camera and the warm water that it's trying to detect. It's analogous to a diver trying to visually identify an object in muddy water, in that the muddy water is absorbing the wavelengths of light that he's trying to detect, and the object can't be detected unless it's inches from his face.

The only other option for detecting the heat signature is by measuring the temperature of the water through which you are cruising, and hoping that you happen to drive right through the target sub's thermal trail, at which point you can start following it like a bloodhound. Odds of encountering a thermal wake in this manner out in the open ocean are vanishingly small.

Note also that the madsci article assumes that the sub is discharging water that is at 100 degrees Celsius. Two points:

1) the actual discharge temperature is undoubtedly classified information, but I'll wager it's a lot less than 100C.

2) if they're discharging their coolant water into their wake, the screws probably do a fantastic job of mixing it with ambient water, lowering the peak temperature of their wake to something very close to ambient.

* Infrared light is light in wavelengths longer than about 740 nm.

Last edited by Machine Elf; 07-20-2011 at 01:40 PM..
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  #8  
Old 07-20-2011, 05:06 PM
R. P. McMurphy R. P. McMurphy is offline
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Information from someone I know that went to Annapolis and did submarine duty:

Diesel subs can actually be quieter than nuclear subs. Seems counter-intuitive.

In real life, a sub's nuclear reactor cannot be shut down. So there is always a signature, albeit very slight. A diesel submarine can charge it's batteries and shut it's engines down. When operating on only battery power there is hardly any signature.
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  #9  
Old 07-20-2011, 08:54 PM
aruvqan aruvqan is offline
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Quote:
Originally Posted by Cabin_Fever View Post
An interesting read.
So if I glean correctly, they do dump their waste heat into the surrounding water. It's just that it is virtually undetectable at depth.


.
Yup. The solution to pollution is dilution, more or less. The ocean is an amazingly huge heat sink.
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  #10  
Old 07-20-2011, 09:08 PM
robby robby is offline
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Quote:
Originally Posted by Cabin_Fever View Post
...How do they manage this heat and not advertise themselves to anyone with their heat signature?
Serious answer: big ocean, small submarine.

Quote:
Originally Posted by R. P. McMurphy View Post
...Diesel subs can actually be quieter than nuclear subs. Seems counter-intuitive.
True statement. Diesel submarines are generally running off of a battery when submerged. Very little speed and endurance, but very quiet. Batteries are very quiet, whereas a nuclear reactor generally requires pumps, etc. that generate some noise.

Quote:
Originally Posted by R. P. McMurphy View Post
In real life, a sub's nuclear reactor cannot be shut down.
Untrue. The reactor can absolutely be shut down. It's done all the time for drills. It's just that the sub is then operating off of its battery and has the same limitations as any other non-nuclear sub. In addition, the battery on a nuclear submarine is generally smaller than those on diesel boats, because it's really only designed for emergency use.
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Old 07-20-2011, 09:11 PM
Polycarp Polycarp is offline
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Quote:
Originally Posted by Cabin_Fever View Post
Okay. I don't doubt the accuracy of these statements.
I just can't fathom (hehe, pun not intended) how dumping 100 degree C water into cooler surroundings can't be detected.
What am I missing here?
Quote:
Originally Posted by runner pat View Post
The sheer volume of surrounding water.
This answer, in a nutshell. Analogy: you're sitting at a table on the deck of your yacht on Lake Superior enjoying a meal when you fumble and knock your salt shaker overboard. Not only does it not turn Lake Superior into salt water, but within minutes you'll be hard pressed to detect any increased salinity in the water adjacent to your boat. Though you're talking a lot more waste heat, you're also talking an enormously greater volume of water for it to disperse in -- and water transmits heat more rapidly than air. (Hence why you get hypothermia from water at a temperature which air would not cause it.)
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  #12  
Old 07-20-2011, 09:12 PM
scr4 scr4 is offline
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I think the main issue is the absorption of radiation by water.

In the air, a hot object - or the air heated by a hot object - radiates infrared radiation. This can easily be detected from a distance because air is mostly transparent to infrared radiation. But water is opaque to infrared.
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  #13  
Old 07-20-2011, 09:54 PM
R. P. McMurphy R. P. McMurphy is offline
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Quote:
Originally Posted by robby View Post

Untrue. The reactor can absolutely be shut down. It's done all the time for drills. It's just that the sub is then operating off of its battery and has the same limitations as any other non-nuclear sub. In addition, the battery on a nuclear submarine is generally smaller than those on diesel boats, because it's really only designed for emergency use.
That's a bit of a nitpick. Of course the reactor can be shut down in an emergency but that is an extreme measure. When the sub is doing what it is designed to do, whether in warfare or on maneuvers, shutting down the reactor is not part of standard procedure (unlike a diesel sub). Shutting down the reactor introduces a whole new host of problems. While it may be done in drills it doesn't mean that the sub it still operational for it's intended purpose. It's more like a fire drill rather than a learned operational warfare procedure.

Last edited by R. P. McMurphy; 07-20-2011 at 09:56 PM..
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  #14  
Old 07-20-2011, 10:02 PM
Whack-a-Mole Whack-a-Mole is offline
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As I understand it modern nuclear subs are quieter than the ambient noise of the surrounding ocean. Can a diesel boat be quieter still? Maybe but not really an issue when the noise you produce cannot be discerned anyway.
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Old 07-20-2011, 10:13 PM
Snnipe 70E Snnipe 70E is offline
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Quote:
Originally Posted by Cabin_Fever View Post
Okay. I don't doubt the accuracy of these statements.
I just can't fathom (hehe, pun not intended) how dumping 100 degree C water into cooler surroundings can't be detected.
What am I missing here?
I highly doubt that the that he condenser water discharge would be 100 degrees C more like 15 to 32 degrees C depending on the sea water temp and the load on the turbines.
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  #16  
Old 07-20-2011, 10:41 PM
R. P. McMurphy R. P. McMurphy is offline
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Quote:
Originally Posted by Whack-a-Mole View Post
As I understand it modern nuclear subs are quieter than the ambient noise of the surrounding ocean. Can a diesel boat be quieter still? Maybe but not really an issue when the noise you produce cannot be discerned anyway.
Let's make a basic, pedestrian analogy the may or may not be appropriate (you tell me).

You are at a rock concert and the drummer is banging away at a level that is measured at a far higher Db levels than the rhythm guitarist. Does that mean that the rhythm guitarist can't be heard? Your ears and just about any recording device could pick up the rhythm guitarist and pick it out. Do you only hear the loudest sounds or do you hear the total composition? But if the rhythm guitarist isn't playing while the drummer is hammering away can it be picked up by your ears or a sensitive hearing/recording device? Can that device tell you that this person in the band is even on the stage?

A little bit of noise is a lot. No noise, that's a different story.
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Old 07-20-2011, 10:58 PM
treis treis is offline
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Originally Posted by Cabin_Fever View Post
Okay. I don't doubt the accuracy of these statements.
I just can't fathom (hehe, pun not intended) how dumping 100 degree C water into cooler surroundings can't be detected.
What am I missing here?
It can be easily detected, if you are close enough. I think there is some confusion about how we use heat to detect the heat signature of airplanes. Every object in the universe emits radiation. You do, I do, the computer does, and so do airplane engines. This radiation is called infrared radiation, and is essentially the same as visible light, just at a bit lower frequency (infra = below and red = the color red). The amount of this radiation depends on the absolute temperature of the object to the 4th power.

Say the temperature of the air is 80F (300K) and the engine is 1000F (800 K). The engine is 2.667 times as hot as the air. Taking that to the fourth power results in a factor of 50. Thus, to something that can see in the infrared spectrum, the engine is going to be 50 times as bright compared to the sky. It's like picking out a spot light against the night sky.

So what's the difference between a plane and a sub? Remember, this infrared radiation acts about the same as light. Since you can see the engine (really, the exhaust ports), your infrared detector can see the radiation as well. Can you see a sub when it is under water? Not really. Most ocean water does a very good job of blocking the light. Even if the sub had a spot light, you would be hard pressed to see it past 30 or 50 feet in most water. Your infrared detector is the same. So the engine might look like a very bright spotlight from 2 feet away, but after 50 feet of water you can barely see it.
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  #18  
Old 07-20-2011, 11:00 PM
leahcim leahcim is offline
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Quote:
Originally Posted by scr4 View Post
I think the main issue is the absorption of radiation by water.

In the air, a hot object - or the air heated by a hot object - radiates infrared radiation. This can easily be detected from a distance because air is mostly transparent to infrared radiation. But water is opaque to infrared.
This. When you're detecting a thermal signature, you're not detecting it like you detect warm streams in public swimming pools (i.e. through direct contact with the warmed water). The ocean's too big for that, and the water moves around too much (and water that is a different temperature from ambient moves around even more because of convection).

Instead you're detecting the IR emitted by the warm object, which only manages to get out a little ways before being absorbed by the water.

This is also why people think "stealth spacecraft" will be pretty much impossible. At first glance operating in space is a lot like operating in an ocean, except there's even more room to get lost in. But without the water to absorb your IR emissions, the heat from just keeping a compartment warm enough to live in is detectable from ridiculous distances.
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  #19  
Old 07-21-2011, 12:27 AM
Whack-a-Mole Whack-a-Mole is offline
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Quote:
Originally Posted by R. P. McMurphy View Post
Let's make a basic, pedestrian analogy the may or may not be appropriate (you tell me).

You are at a rock concert and the drummer is banging away at a level that is measured at a far higher Db levels than the rhythm guitarist. Does that mean that the rhythm guitarist can't be heard? Your ears and just about any recording device could pick up the rhythm guitarist and pick it out. Do you only hear the loudest sounds or do you hear the total composition? But if the rhythm guitarist isn't playing while the drummer is hammering away can it be picked up by your ears or a sensitive hearing/recording device? Can that device tell you that this person in the band is even on the stage?

A little bit of noise is a lot. No noise, that's a different story.
I dunno.

In theory any noise is, well, noise. Any sub has to make some if only from the water passing by the hull. The question is can an enemy discern that sound and know the sub is there? You need to be able to peel that unique sound signature out of the background noise. Modern computers can do that to an extent but there are always limits and the sound environment under water is complex.

I have heard that diesel subs are astonishingly quiet but I have also read that modern US nuclear subs are deemed black holes in the water. They are exceptionally hard to track via hearing them.

I think at this point it is splitting hairs. Diesel quieter than a nuke? Maybe but you aren't likely to hear either one sneaking up on you.

Last edited by Whack-a-Mole; 07-21-2011 at 12:29 AM..
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  #20  
Old 07-21-2011, 12:43 AM
Whack-a-Mole Whack-a-Mole is offline
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I'll note when I was growing up there was a naval air station in my city (Glenview Naval Air station which is now long gone). They had a variety of planes there but mostly they had P-3 Orions based there which had Magnetic Anomaly Detectors (MAD) which they used to detect submarines (you can see it in the picture...that long thing sticking out the back).

A sub is a big hunk of metal and supposedly this would distort the earth's magnetic field which this plane could detect.

I have not heard of them in a long time though. Not sure if they are still used or other/better methods have been developed to replace them.
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  #21  
Old 07-21-2011, 12:57 AM
R. P. McMurphy R. P. McMurphy is offline
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Originally Posted by Whack-a-Mole View Post
I dunno.

In theory any noise is, well, noise. Any sub has to make some if only from the water passing by the hull. The question is can an enemy discern that sound and know the sub is there? You need to be able to peel that unique sound signature out of the background noise. Modern computers can do that to an extent but there are always limits and the sound environment under water is complex.

I have heard that diesel subs are astonishingly quiet but I have also read that modern US nuclear subs are deemed black holes in the water. They are exceptionally hard to track via hearing them.

I think at this point it is splitting hairs. Diesel quieter than a nuke? Maybe but you aren't likely to hear either one sneaking up on you.
Yea, we are probably splitting hairs. What I am getting at is that, according to my guy, the diesel sub can turn off it's engines, sit on the bottom of the ocean and look like nothing other than a rock amid a million rocks. The nuclear sub can attempt the same thing but due to the fact that the reactor is still operating, there is a signature. One can be located, the other can't other than mapping its last location. I don't know what the radius is for a diesel sub operating on batteries is but it is capable of moving from the spot where is was last identified. See what I mean? Then it can sit and wait. Of course, when the diesel engines reactivate it is readily detectible but the game of cat and mouse can get very interesting.
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  #22  
Old 07-21-2011, 01:04 AM
Declan Declan is offline
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Originally Posted by Whack-a-Mole View Post
As I understand it modern nuclear subs are quieter than the ambient noise of the surrounding ocean. Can a diesel boat be quieter still? Maybe but not really an issue when the noise you produce cannot be discerned anyway.
Layman ansewer would be yes, the nuke boats would have pumps that can be heard, in the movie the hunt for red october, you have that one scene where Jonesy is breaking down that audio tape and you can hear the thrumming of the pumps.

In submerged mode, the diesel electrics are just electric motors. The only problem with them, is that they are like a bucket, go faster and you empty the bucket that much faster , so they have to practice conservation of energy

Lurking around at station keeping speed, would increase their time on station relative to the amount of supplies that they would have, where as moving at flank speed may reduce the batteries to hours worth of usable energy.

Too many people are calling them mobile mine fields now anyways. Their silence is golden if they get to fire the first shot and after that the detection radius is really small.

Declan
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  #23  
Old 07-21-2011, 01:38 AM
Whack-a-Mole Whack-a-Mole is offline
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Originally Posted by R. P. McMurphy View Post
Yea, we are probably splitting hairs. What I am getting at is that, according to my guy, the diesel sub can turn off it's engines, sit on the bottom of the ocean and look like nothing other than a rock amid a million rocks. The nuclear sub can attempt the same thing but due to the fact that the reactor is still operating, there is a signature. One can be located, the other can't other than mapping its last location. I don't know what the radius is for a diesel sub operating on batteries is but it is capable of moving from the spot where is was last identified. See what I mean? Then it can sit and wait. Of course, when the diesel engines reactivate it is readily detectible but the game of cat and mouse can get very interesting.
Modern sub warfare is not anything like WWII sub warfare.

No one puts their sub on the bottom and makes like a rock anymore. I suppose it could happen but it is very unlikely.

The US sub fleet is a blue water (i.e. deep water) fleet. The ocean floor is waaaaay below where they can go. We have two types of sub...boomers and fast attack subs. Boomers strictly stay in deep, deep water. They have no need of getting in coastal waters. Fast Attack subs may go anywhere but usually they stay in deep water too. Even when they do go in shallow waters (to insert SEALS or do land attack missions) they are not there for long. They do their thing and scoot and they are quite fast...fast enough many surface ships would have trouble closing on them.

Also note in modern warfare a sub almost certainly knows what is remotely near them on the surface. They will not disclose their position by firing (or whatever) if they have reason to believe there is a surface ship close enough to cause them trouble. In WWII they could not know these things. Modern subs also have vastly superior torpedoes with brains of their own not to mention Tomahawk missiles such that they can shoot accurately from far greater range than a WWII sub.

A diesel sub I think is quieter but as mentioned this is splitting hairs. You are almost certainly not going to know the sub is there till it shoots at you and unless you have assets very near the sub when it shoots it'll be long gone by the time you get there to shoot back. Helicopters/planes are your best bet.

And, in the end, the ability of a nuke to not have to surface to recharge batteries is a greater advantage than the diesel being somewhat quieter. Modern diesel subs are a far cry from WWII subs but in the end their advantage is time limited and then they are vulnerable. The slightly noisier nuke has advantages that more than make up for it.
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Old 07-21-2011, 01:43 AM
Whack-a-Mole Whack-a-Mole is offline
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Quote:
Originally Posted by Declan View Post
Layman ansewer would be yes, the nuke boats would have pumps that can be heard, in the movie the hunt for red october, you have that one scene where Jonesy is breaking down that audio tape and you can hear the thrumming of the pumps.
FWIW in that movie the noise he hears is the unique sound of the Caterpillar Drive. That propulsion system was, in the movie, supposed to make the Red October undetectable but Jonesy (and an Alpha captain) manage to isolate the unique sound the sub makes using that drive and could program a computer to pick out that particular sound (remember in the movie the computer identified it as a geological anomaly...or something because it was originally programmed to look for geological events). Unless you knew what to look for the sub was uber-stealthy which made it scary.

Pumps had no part in it.
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  #25  
Old 07-21-2011, 01:56 AM
clairobscur clairobscur is offline
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Originally Posted by R. P. McMurphy View Post
Diesel subs can actually be quieter than nuclear subs. Seems counter-intuitive.
.

Not counter-intuitive at all, since they can run on batteries. That's the main advantage of diesel subs, in fact.

For this reason, they're more useful than nuclear subs for coastal defense, since they can be almost perfectly silent and come back to a safe heaven when their batteries run low (rather than keep sailing using thier diesel engine). Could be useful for an escort, too, since the ships they'll be following will be detectable anyway, and they can switch to batteries when needed for action.

FTR, all French attack submarines (as opposed to ICBM-launching subs) run on diesel. The general idea being that they would switch to batteries when reaching the zone of operation.
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Old 07-21-2011, 02:07 AM
TriPolar TriPolar is offline
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Somewhat of a change of direction here. I recall at one point hearing that we could track Soviet submarines from their wake given a known starting point and direction. Was that just Cold War hype, or were we capable of interpreting the effect on the surface of a sub traveling deep under water?
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  #27  
Old 07-21-2011, 02:16 AM
kombatminipig kombatminipig is offline
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Originally Posted by Whack-a-Mole View Post
And, in the end, the ability of a nuke to not have to surface to recharge batteries is a greater advantage than the diesel being somewhat quieter. Modern diesel subs are a far cry from WWII subs but in the end their advantage is time limited and then they are vulnerable. The slightly noisier nuke has advantages that more than make up for it.
Modern Stirling AIP engines give non-nukes the ability to run at depth for as much as a few weeks, in fact.
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Old 07-21-2011, 02:21 AM
Whack-a-Mole Whack-a-Mole is offline
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Somewhat of a change of direction here. I recall at one point hearing that we could track Soviet submarines from their wake given a known starting point and direction. Was that just Cold War hype, or were we capable of interpreting the effect on the surface of a sub traveling deep under water?
Never heard of that (which frankly means nothing...I am no expert).

IIRC there was a time during the Cold War where the US was excellent at tracking Soviet Subs. There is a story, do not know if it is true, that the US had all their subs following Soviet subs ping them (an unmistakable sign someone is right on top of you). They did this simultaneously. It was a message writ large to the Soviets that when it came to subs we had their number.
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Old 07-21-2011, 02:26 AM
Whack-a-Mole Whack-a-Mole is offline
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Originally Posted by kombatminipig View Post
Modern Stirling AIP engines give non-nukes the ability to run at depth for as much as a few weeks, in fact.
A Stirling engine sub?

The issue is being quiet. Electric engines run off batteries are quiet. But batteries need recharging so you run the significantly noisier diesel engines to do that. Is a Stirling engine somehow silent?

Nukes are noisier than a ship on batteries but quieter than a ship running diesel.

As with most things your choice is a tradeoff. You have to decide the role for the ship and make the best compromises you can.
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Old 07-21-2011, 06:27 AM
Mines Mystique Mines Mystique is offline
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Originally Posted by Whack-a-Mole View Post
I dunno.

In theory any noise is, well, noise. Any sub has to make some if only from the water passing by the hull. The question is can an enemy discern that sound and know the sub is there? You need to be able to peel that unique sound signature out of the background noise. Modern computers can do that to an extent but there are always limits and the sound environment under water is complex.

I have heard that diesel subs are astonishingly quiet but I have also read that modern US nuclear subs are deemed black holes in the water. They are exceptionally hard to track via hearing them.

I think at this point it is splitting hairs. Diesel quieter than a nuke? Maybe but you aren't likely to hear either one sneaking up on you.
The noise from the nuke depends a great deal on the speed of the sub. In most modern subs there is a mode where the coolant is circulated via convection rather than being pumped. This eliminates the noise from the pumps, allowing the sub's sonic signature to be very, very small.
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  #31  
Old 07-21-2011, 08:57 AM
wevets wevets is offline
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Originally Posted by clairobscur View Post
FTR, all French attack submarines (as opposed to ICBM-launching subs) run on diesel. The general idea being that they would switch to batteries when reaching the zone of operation.
The French seem to have a number of nuclear attack submarines of the Rubis class - do you mean that they run them without the reactor or ?
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  #32  
Old 07-21-2011, 04:48 PM
kombatminipig kombatminipig is offline
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Originally Posted by Whack-a-Mole View Post
A Stirling engine sub?

The issue is being quiet. Electric engines run off batteries are quiet. But batteries need recharging so you run the significantly noisier diesel engines to do that. Is a Stirling engine somehow silent?

Nukes are noisier than a ship on batteries but quieter than a ship running diesel.

As with most things your choice is a tradeoff. You have to decide the role for the ship and make the best compromises you can.
I honestly don't have any idea of how much noise a Stirling AIP engine makes submerged, and I'm guessing that whoever could tell me would probably have to kill me afterwards.

As you say, I'm guessing that even they'll run off batteries while being actively hunted. The air independent propulsion system does on the other hand allow the sub to stay submerged and load their batteries at depth, which I think lowers the chance of getting caught by patrol craft.
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  #33  
Old 07-21-2011, 07:43 PM
ZenBeam ZenBeam is offline
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Originally Posted by Whack-a-Mole View Post
IIRC there was a time during the Cold War where the US was excellent at tracking Soviet Subs. There is a story, do not know if it is true, that the US had all their subs following Soviet subs ping them (an unmistakable sign someone is right on top of you). They did this simultaneously. It was a message writ large to the Soviets that when it came to subs we had their number.
I can not believe that is true. If we had their number, we wouldn't want them to know that we did.

I could believe that perhaps someone determined we could do that, and the story got stretched a bit.
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  #34  
Old 07-21-2011, 08:40 PM
Blackhawk441 Blackhawk441 is offline
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Originally Posted by robby View Post
The reactor can absolutely be shut down. It's done all the time for drills. It's just that the sub is then operating off of its battery and has the same limitations as any other non-nuclear sub. In addition, the battery on a nuclear submarine is generally smaller than those on diesel boats, because it's really only designed for emergency use.
Technically, yes, but that would never, ever happen. A nuke boat is not designed for serious maneuvers on electric power, and I highly, highly doubt it would be seriously combat capable (yes, it could launch torpedoes and such, but not maneuver at all) without the reactor running.

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Originally Posted by Whack-a-Mole View Post
The US sub fleet is a blue water (i.e. deep water) fleet. The ocean floor is waaaaay below where they can go. We have two types of sub...boomers and fast attack subs. Boomers strictly stay in deep, deep water. They have no need of getting in coastal waters. Fast Attack subs may go anywhere but usually they stay in deep water too. Even when they do go in shallow waters (to insert SEALS or do land attack missions) they are not there for long. They do their thing and scoot and they are quite fast...fast enough many surface ships would have trouble closing on them.
You're 100% right on the boomers; they aren't there to do anything but be a deterrent.

688(I)s or Seawolfs, however, could definitely be used in shallower waters depending on what COMSUBPAC/LANT wants them to do. Tomahawks don't have unlimited range, and they may have to venture into shallow waters to launch; they may also be assigned to interdict surface ships or subs, or blockade a port. Shallow waters ops are definitely plausible for attack subs.

If they were in shallow waters, they likely wouldn't scoot as soon as they engaged, anyway- as quiet as our subs are, at flank speed, nothing comes close to silent, and they could be picked up for miles away. Our Silent Service's typical modus operandi is just that-silent in, silent out.

Regardless of all that, you don't necessarily have to literally be on the seafloor so be silent- the main advantage of diesel/electric subs over nukes is that when running silent and at a full stop, diesels are pretty much completely silent- the only sound coming out of them will be the crew dropping wrenches and shit like that. (Depending, of course on the sub- there are a million things that could make noise, but the crew usually gets on that when rigged for silent running). In the same circumstances, a nuke does have to run its coolant pumps or overheat the reactor and have bad things happen.
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  #35  
Old 07-21-2011, 11:31 PM
robby robby is offline
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Originally Posted by R. P. McMurphy View Post
Information from someone I know that went to Annapolis and did submarine duty...
I'm a former submarine officer myself.

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Originally Posted by R. P. McMurphy View Post
In real life, a sub's nuclear reactor cannot be shut down.
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Originally Posted by robby View Post
Untrue. The reactor can absolutely be shut down. It's done all the time for drills. It's just that the sub is then operating off of its battery and has the same limitations as any other non-nuclear sub. In addition, the battery on a nuclear submarine is generally smaller than those on diesel boats, because it's really only designed for emergency use.
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Originally Posted by R. P. McMurphy View Post
That's a bit of a nitpick. Of course the reactor can be shut down in an emergency but that is an extreme measure. When the sub is doing what it is designed to do, whether in warfare or on maneuvers, shutting down the reactor is not part of standard procedure (unlike a diesel sub). Shutting down the reactor introduces a whole new host of problems. While it may be done in drills it doesn't mean that the sub it still operational for it's intended purpose. It's more like a fire drill rather than a learned operational warfare procedure.
I don't disagree with anything you've said here in your second post.

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Originally Posted by Blackhawk441 View Post
Technically, yes, but that would never, ever happen. A nuke boat is not designed for serious maneuvers on electric power, and I highly, highly doubt it would be seriously combat capable (yes, it could launch torpedoes and such, but not maneuver at all) without the reactor running.
I don't disagree with anything here, either.


To both of the previous posters: I said nothing about whether or not a nuclear sub would shut down its reactor in a tactical or operational situation. I was simply responding to Mr. McMurphy's initial statement that "In real life, a sub's nuclear reactor cannot be shut down."

First off, the statement is nonsensical in and of itself. Of course a submarine's nuclear reactor can be shut down. Even I grant that you meant that a sub's reactor cannot be shut down while operating at sea, it's still wrong. As I stated, the reactor on operating submarines is shut down all the time for drills. I should know, considering that I've conducted fast recovery startups at sea more times than I can remember.
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  #36  
Old 07-21-2011, 11:42 PM
TriPolar TriPolar is offline
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Originally Posted by Whack-a-Mole View Post
Never heard of that (which frankly means nothing...I am no expert).

IIRC there was a time during the Cold War where the US was excellent at tracking Soviet Subs. There is a story, do not know if it is true, that the US had all their subs following Soviet subs ping them (an unmistakable sign someone is right on top of you). They did this simultaneously. It was a message writ large to the Soviets that when it came to subs we had their number.
There appears to be something to this. But it could still just be something we want others to believe.
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  #37  
Old 07-22-2011, 01:11 AM
Declan Declan is offline
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Originally Posted by ZenBeam View Post
I can not believe that is true. If we had their number, we wouldn't want them to know that we did.

I could believe that perhaps someone determined we could do that, and the story got stretched a bit.
Nope, I doubt the part about pinging them, but the USN was trailing soviet boats the minute they left port, their boomers anyways. Then a guy named Walker told the soviets that it was happening and made the soviets a bit paranoid, enough that a maneuver called a crazy ivan was invented.

Since subs are blind in the baffles , unless they have a special acoustic sensor trailing out the rear, would abruptly turn ninety degrees to either port or starboard. Very irratating to anyone who happened to be tailgating at the time.

Declan
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  #38  
Old 07-22-2011, 09:35 AM
muldoonthief muldoonthief is offline
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Originally Posted by ZenBeam View Post
I can not believe that is true. If we had their number, we wouldn't want them to know that we did.

I could believe that perhaps someone determined we could do that, and the story got stretched a bit.
This sounds like a sub version of the Fake bomb on the decoy airfield story. What would be the point of letting the Soviets know we could trail them?
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  #39  
Old 07-22-2011, 10:20 AM
Blackhawk441 Blackhawk441 is offline
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Originally Posted by robby View Post
I should know, considering that I've conducted fast recovery startups at sea more times than I can remember.
By all means, I cede to your expertise then.

Just out of curiosity, what classes of subs did you serve on? About how long would it take to restart a reactor? I have trouble thinking of a situation where the reactor would have to be shut down yet would not cause enough permanent damage to allow it to be restarted.
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  #40  
Old 07-22-2011, 11:47 AM
BMalion BMalion is offline
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robby, Thank you for your service. I'm jealous. I always thought that if I had joined the armed forces, it would be the Navy, and Submarines would be my preference.
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  #41  
Old 07-22-2011, 11:51 AM
MichaelEmouse MichaelEmouse is online now
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Originally Posted by muldoonthief View Post
This sounds like a sub version of the Fake bomb on the decoy airfield story. What would be the point of letting the Soviets know we could trail them?
Perhaps getting them to abandon/deemphasize this particular means of nuclear weapons delivery? Even if the US was superior in this aspect, it might have disliked the use of nuclear weapons launching subs.
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  #42  
Old 07-22-2011, 05:08 PM
Cabin_Fever Cabin_Fever is offline
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Wow. Let me apologize for being absent from this thread for so long. I certainly didn't expect this many replies.
Thank you all for the explanations to my query, and for all the extra tidbits about submarines.
It certainly enlightened me in more ways than one.
Thank you!
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  #43  
Old 07-23-2011, 01:15 PM
robby robby is offline
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Originally Posted by Blackhawk441 View Post
By all means, I cede to your expertise then.

Just out of curiosity, what classes of subs did you serve on?
I was a junior officer on an improved Los Angeles-class fast attack submarine. I also did a strategic deterrent patrol on an old James Madison-class fleet ballistic missile submarine.

Quote:
Originally Posted by Blackhawk441 View Post
About how long would it take to restart a reactor? I have trouble thinking of a situation where the reactor would have to be shut down yet would not cause enough permanent damage to allow it to be restarted.
The most common reason a reactor is scrammed is for drills. Once the cause of the trip is determined (i.e "Reactor SCRAM due to [Chief] Engineer tripping the scram switch"), it can be rapidly restarted via a fast recovery startup.

Other causes of reactor SCRAMs (or trips) include automatic SCRAMS caused by the protective equipment. Most often these unintentional trips occur (which does not happen very often) when the protective circuitry is being tested.

Automatic SCRAMs can also be caused by failure of critical equipment (such as failure of a reactor coolant pump). In such cases, the reactor is designed to automatically shut down specifically to prevent damage to the reactor. In many cases, because U.S. naval reactors are also designed for robustness, operators can quickly shift to backup equipment and restart the reactor with little interruption.

If the equipment casualty is relatively minor (such as an auxiliary pump), it is easy to switch to backup equipment without involving a reactor shutdown at all.
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  #44  
Old 07-23-2011, 02:46 PM
clairobscur clairobscur is offline
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Originally Posted by wevets View Post
The French seem to have a number of nuclear attack submarines of the Rubis class - do you mean that they run them without the reactor or ?
I mean that I was mistaken

Sorry for the non-factual statement and the spreading of some of my ignorance..
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  #45  
Old 07-23-2011, 02:57 PM
clairobscur clairobscur is offline
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Originally Posted by clairobscur View Post
I mean that I was mistaken

Sorry for the non-factual statement and the spreading of some of my ignorance..

Worse than that : after checking, there's *no* non nuclear French submarines. Don't know where I picked the false info. Sorry again.
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  #46  
Old 07-23-2011, 06:16 PM
Whack-a-Mole Whack-a-Mole is offline
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Originally Posted by TriPolar View Post
There appears to be something to this. But it could still just be something we want others to believe.
My Google-Fu is failing me.

I am sure I have heard the story that the US did this. I am pretty sure I heard Tom Clancy relating this story. Yes he is a writer of fiction but my recollection is this story was true.

As to why we'd do this it was supposedly a message Reagan wanted to send that we had the Soviets number in this respect. The Soviets of course had spies in our government and their sub driver probably knew they were often followed. I am not sure there was a big secret that this happened (as noted the Soviets took to using the Crazy Ivan maneuver to try and shake US subs pursuing them). Pinging all soviet subs at the same time sent a message loud and clear that we had their number. It may seem silly but if they kind of already knew this was the case the effect is more a punctuation mark to a message than anything else. Also, knowing you are being followed doesn't change much in this respect so it is not messing things up for the US sub drivers.
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  #47  
Old 07-25-2011, 01:22 AM
Blackhawk441 Blackhawk441 is offline
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Originally Posted by robby View Post
I was a junior officer on an improved Los Angeles-class fast attack submarine. I also did a strategic deterrent patrol on an old James Madison-class fleet ballistic missile submarine.

The most common reason a reactor is scrammed is for drills. Once the cause of the trip is determined (i.e "Reactor SCRAM due to [Chief] Engineer tripping the scram switch"), it can be rapidly restarted via a fast recovery startup.

Other causes of reactor SCRAMs (or trips) include automatic SCRAMS caused by the protective equipment. Most often these unintentional trips occur (which does not happen very often) when the protective circuitry is being tested.

Automatic SCRAMs can also be caused by failure of critical equipment (such as failure of a reactor coolant pump). In such cases, the reactor is designed to automatically shut down specifically to prevent damage to the reactor. In many cases, because U.S. naval reactors are also designed for robustness, operators can quickly shift to backup equipment and restart the reactor with little interruption.

If the equipment casualty is relatively minor (such as an auxiliary pump), it is easy to switch to backup equipment without involving a reactor shutdown at all.
Very interesting, thanks for the reply. Figures that the nuclear circuit breakers (band name!) would trip the most while testing it. At least they left them on, unlike Chernobyl
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