Having seen the tender mask broadband noise as we neared it on a BQQ5 I can say it can certainly happen. Given the small size of a kilo I would guess that is pretty close to the range it would become obvious on the display. A Typhoon would block out probably 3x more distant. Of course you should have detected one of those well before that distance. I doubt even an aircraft carrier would create a noticeable shadow beyond 1000 yards.

Of course you have to add to that the need to have been at the appropriate depth and/or D/E to get a shadow at all.

Ok, this brings a question to my mind: on a nuke sub, a generator is running to provide on-board power to my systems, that generator has mostly a frequenzy of 50 hz, as it generates the same power as provided at home, i believe. (it would make sense though) this is modeled in-game as most ships and subs have the first line on or next to 50 hz on NB.

Now the kilo is a diesel-electric-sub, and my common sense, correct me if im wrong, tells me that all the systems are not powered by a generator but from the batteries. Only problem I see are transformators running to provide a different voltage. it should still be a lot quieter than the nuke-sub generator?

I'd say so. In a nuke sub, you also need to continuously run the coolant pumps as well...or shut down your reactor.

a diesel-electric sub on batteries should be VERY quiet.

...then why not add batteries to a nuke sub for moments of VERY silent running? Is the cooling system too demanding in engery?

from what I understand, nuke subs DO have batteries. (mostly for backup/emergency power) but its the pumps that make noise, not the reactor. If you shut off the pumps, you get a meltdown (because you're not cooling the reactor) or possibly an explosion. Shutting down the reactor entirely (and starting it again) is a difficult process and takes time to do properly. its really not worth the trade off in being that silent. Just ADCAP the f**ker from long range before he ever hears you...haha. You get my meaning.

Nukes CAN run without pumps .. Submarine reactors are rather different from civilian power plants. They can be cooled by convection alone. Not so hard when there are tons of water all around you. Most nuclear subs can run slow on reactor without pumps running.
They can also shut the reactor down completely .. and run on batteries .. even if for just a short time.

Dr Sid is right. Some submarine nuclear reactors can run without pumps for periods of time. A good example is the S8G, mounted in Ohio class submarines. It uses a concept called "natural circulation" and can run that way at greatly reduced power. The general rule for nuke subs though, is that they arent as quiet as they newest diesel boats can be. There is room for debate however....could say an Astute class rigged for full silent running be as quiet as a Gotland class? Good question, but again things like water depth and speed would be a factor as well.

simple chemistry and physics apply. sound is generally created by friction, friction is created by something moving. Less moving, less noise.

Late comer to the party.. but some insights.

The batteries on a nuke boat are for emergencies. Just ONCE did I see us shut it all down and run on the EPM (Emergency Propulsion Motor). We ran the AUTEC course then had to recrit the plant quickly as the amps were ticking away. Why did we do it? We wanted to isolate EVERYTHING from our noise profile that could be removed. No fans, coolers, pumps, etc. We have ONE DC lube oil pump and that was IT. The only noise we had was the propulsion train and the screw.

On a USN Nuclear sub, the battery was there for emergency reactor startup and that was the sole criteria of its size. We had to be able to go from a cold plant (we are talking COLD as in not hot enough to make steam) to critical (and making steam) and one SSTG operating with just the amps available in a fullly charged battery and NO OTHER SOURCE OF POWER. In the event of the loss of shore power and the inability to start the diesel generator, you had a checklist that you had and strict go/no go timelines. The colder the plant, the shorter the decision tree was. This was practiced and walked thru several times a year in training.

Speaking of the S8G and other natural circ plants you are kinda correct. They can operate in a low power mode but do not think that is limited to a low speed. Remember, speed if a function of power. To double your speed, you have to increase your power by a factor of 4. It is a log function.

If you limit ANY nuke sub to half power its max rated power, you are only restricting it from the top 25% of its max speed.

Let that sink in for a sec.

So.. if you restricted the plant to say 20% of max power in NC mode, you are limiting it to what percentage of its max speed?

The REAL benefit of NC is the reduction in operational noise. You turn off what are the biggest sources of noise in a nuc boat. You can dramatically reduce the noise profile without reducing its tactical readiness significantly. And just remember, full power mode is a simple flick of a switch away.

And yes, I am(was) a qualified S6G/S8G watchstander. I could tell you all kinds of neat things about both plants that would boggle your mind. Since the Seawolf/Virginia class reactors were based off the S8G, I could probably fill in a lot of blanks on those plants as well.

Back to the detect a diesel boat question:

When I was in, almost 20 years ago now, there was a neat thing going on with sonar and the processing power we had. We could actually isolate a line a bearing that had lower background noise. Yep, you could localize an area of QUIETER background noise. If that area of noise was at 200 feet and moving at 3 knots.. well.. you can imagine all the possibilities.

I image things have improved since then.