The S6W reactor core was first taken critical in the S8G prototype plant in upstate NY. Seeing as how the S8G is publically stated to be a nactural circ reactor it is a pretty safe bet that the S6W is as well. When you look at the thermal and hydraulic design limits and parameters of a reactor core, you do not just 'drop it in' a plant that does not meet these requirements. A power plant is designed to handle the core, not vice versa. The S6W plant is the one that drives the Seawolf class.

Something else you might not know. A 688 was originally supposed to have a natural circulation plant. When you look at the plant layout there are many similarities with the S8G plant design. However, there was insufficent hydraulic head to get sufficient flow in the plant to conduct power ops. Basically, the hull was not big enough. This meant that the quieter natural circulation could not be used to lower the noise signature.

Is the S9G natural circulation? I would hope so, but the VAs are smaller. I do have an extremely hard time visually differentiating the Seawolf and Virginia classes, other than the general perception of the Seawolves as a bit stouter.

Unfortunately, I got out before the VA class was really being discussed. While I was in they were still calling it the NSSN concept, not the VA class.

However, with the advent of computer aided design (the seawolf was the first US sub to use this btw) I am sure they can pull tricks off that would have been speculation only a decade before. A nuc sub is not designed in a year or 3. It takes a DECADE of planning and engineering analysis before the first order is even made.

Thanks for the perspective BH, insightful as always.

As for VA, my guess... as a complete and utter layperson... is that there's probably a reason the Virginia Class has the same payload, crew size, yet is almost 1000 tons larger than the 688 (7800 tons vs 6900 tons). Probably extra room in the engine compartment for a NC reactor (bigger than the LA, but smaller than the SW) and/or other quieting techniques.

I worked on further on my modification with DWEdit. And this is the result.
A very simple mod :). Thought I share it with you. Comments are welcome.

http://www.subsim.com/radioroom/show...897#post971897

Don't forget the steam turbines that actually turn the prop shaft. Bigger sub = more room for queiting those.

Also the 688(i)s and SW have ancotic (sp?) tiles which US subs lacked for a very long time. Those not only absorb active sonar pings they also absorb sub self noise. Which is one of the reasons Russian subs are queit at low speeds (two hulls with these tiles).

To be quite honest here, the reason they are quieter is due to the MASSIVE improvements in pump impeller designs gained when Toshiba sold them all the fancy metal milling machines. The predominate noise produced by a nuclear sub is not from the screw, but from the gear used to run and support the reactor plant.

While they got the quieter pump impellers, they still have the lousy screw designs that were optimized for speed and acceleration rather than stealth. At a slow enough speed, even these screws were pretty quiet. Thus you have a quiet boat at slow stalking speeds. As soon as they start cranking up the RPM'S they are just as loud as ever. Their reactor plants also have some fundemental differences in operation from the American boats that showed a greater noise impact from the improved impeller construction.

Why did they design the screws for speed and acceleration you ask? The plants were noisy as heck so why not make it a better performer. A quieter screw had no purpose. Thus they were better equipped to runout maneuver a torpedo. If you can get up to top speed fast enough, you could get out of the aquisition cone of the incoming torpedo.

Also, there was a funamentel difference in MISSION between US and the Soviet subs. Ours was a forward offense mission while theirs was more home water defense. A boat had to be able to move QUICKLY to get into an intecept position based on external data. Thier boats works as teams with surface and/or air assets while our boats operated in a more independant ops mode.

Well better screws were a part of it but not as you think, the screws of the 3rd Gen Russian subs (Typhoon, Oscar, Akula, Sierra, Mike) were designed before that, the Japanese and Norwegian “scandals” simply allowed the Russians to build their own designs of better quality and faster.

When I talked about quieting I was thinking of 1st Gen subs. It might be hard to believe but the early Russian subs were stealthy than ours at low speeds thanks to anechoic tiles on that big double hull of theirs. The US 1st gens nucs were noisier than the WWII fleet boats! Nautilus was renowned for its self noise over 8 knots, in fact she was a test bed for experiments relating to that. I know Bill our Master of Defense has shared several stories about their time as a test bed sub.

Back to Russia in the 80's reactors were also quieted the OK-650a was capable of natural circulation for cooling at low speeds. The Sierras used this reactor, the Akula's have a similar plant the OK-650b same as the Oscar. (The Typhoon had the OK-650, the Mike the OK-650b-3) Latter Russian boats also have “Active Noise Cancellation” systems which I've never heard of US boats having.

Yea, this is a few years old, but i'm bumping this -

I'm attempting the same thing in the Reinforce Alert Mod- I have DWedit, and have been doing a ton of 1 on 1's with hostile Virginia's against me driving a Seawolf - and they've been slinging adcaps at me while i couldn't detect their subs, only their torpedoes when they shoot at me- and i'm not close enough for their high frequency sonar to see me, and i usually bounce between 2 knots and 10, but they find me every single time(before i find them)..... at about a nm range of no more than ten or so...(both the base seawolves and the jimmy carter)


Maybe i need to pilot the virginia against a seawolf..and see if it happens again...lol. :/\\!!


-crazy ivan posted the actual sound chart spreadsheet here on this page as a download
http://www.redrodgers.com/forums/sho...d.php?p=137040

-but when i look in DWedit, it doesn't match up- the spreadsheet might be out o date, as i'm on 1.3.7 RA, but...its was hardly 2 pages back...from the 1.3.7 mod...

If you look at the spreadsheet - for the virginia and seawolf at 0 knots
-virginia is at 58, seawolf is at 57 , and the jimmy carter(it's seperate from the first 2 seawolves in the database) is at 57

Now i open up Dwedit, and look at the object dialog menu , and pull up the seawolf and virginia, and the passive sonar SL has the virginia at 53, the seawolf at 54, and the jimmy carter at 57...
I'm having trouble making sense of what this means- it looks like DWedit is saying the virginias emit less sound in general than the seawolves(let alone it's looking like the jimmy carter went BACKWARDS in that it's louder, unless i'm reading this backwards and i dont think i am, as the 688i's have higher numbers.

so i open up the thrust dialog menu in DWedit , and looking at the numbers ,, it has base noise and speed noise
virginia base noise 3, speed noise is 16
seawolf base 0 , speed noise is 17,
and then jimmy carter(under 0044, it shares the same one with 2 other subs, the amethyste and astute) -is set at base 0, speed noise 18


..I don't understand what this means.
Can anyone help me make sense of these numbers?


So if it's thrust dialog- then the seawolf at zero is quieter, but at full speed is louder than the virginia at full speed, and the jimmy is even louder??? Or does the passive Sonar SL thing in the object dialog menu mean the virginia is quieter with it's 53?

My goal is to see if the Virginia are somehow set as quieter, and if so, to use DWEdit to make the seawolves match the virginias ...So i can quit getting owned* by my cheaper , lesser-capable alternative
*to be fair, i have defeated virginias in the seawolves in one on ones, but i'm still suspect about who's superior noise-level wise.


I know the original posters aren't around, 5 years later, but i'm a bit surprised to hear pumpjets aren't as efficient as open propellers - thrust wise, i thought pumpjets are better. Sort of how like turbojets are better than open propellers if they are at high speed(yes in low altitude dense air ,props aren't bad)





Reading this, I still am not sure how to make sure the virginias aren't quieter than the seawolves, because these 1 on 1 fights don't include a lot of running around at top speed, - the passive sonar is what is confusing me. If you add base noise + speed noise, the virginias are indeed louder than the seawolves- but that passive Sonar level thing from the object dialog menu.....???????

So you will have to decide what "quieter" means. You can give the SW and the Virginia the same passive/base noise level which will make them equally quiet at stop.

Then you will have to calculate the amount of noise added per knot from the thrust menu for the SW (or Virginia, whichever you decide to use as your standard) and decide the value of the "speed noise" in the other boat's thrust menu that will grant the same amount of noise/knot.

They will then have equal noise emissions at each speed, with the caveat that since the SW is faster, as it passes the Virginia's max speed it will then exceed the Virginia's noise levels.

Another approach is to make each boat the same noise at each's respective top speed, but the result will be that the SW will also be quieter than the Virginia at any equal speed.

Hope that makes sense.

LB

..Seems some people are still here, 5 years later, wow.

Anyway, thank you very much for the response. I That thrust dialog doesn't make it easy to figure out though how much louder it gets per knot- I suppose you have to divide the speed noise into how many knots? Seawolf is base 0, then speed 17 - the seawolves i have set to a flank speed of 40 knots(stock DW is 40, RA puts them at subcommand's 35, i undid that)

..17/40 is .0425... so for every knot, , the noise goes up by .425, eh?


Hm, then if i set the Seawolf and Jimmy carter passive sonar level to the Virginia's 53..(or maybe 52)- then all that's left is the 0 -17 speed noise of SW, and 3 - 16 vir

Except, as you mentioned 5 years ago, that's 3 +16.(for the Vir) So it's 19, compared to 0 +17 at top speed(SW) So all i need to do is make the passive sonar level 53 , and the SW is quieter off the bat. Or 52....


Thanks for the advice LoBlo :D

In my opinion assigning "basenoise" in the thruster dialog is redundant as it only adds to the Passive Sonar SL in the object dialog, so only leads to confusion. Better to level the Basenoise in the thrust dialog as 0 IMHO.

Also, I'm not sure if I you mentioned it above or if I missed it, but remember that if you give the SW and the Virginia the exact same Passive Sonar SL and the exact same Speednoise, you are in fact making the SW quieter than the Virginia at any given speed.

In your example with the SW given a Passive Sonar SL of 53 and a thrust SpeedNoise of 0 + 17, it grants 0.42 (there's a typo in your above math) increase in noise per knot of increased speed. If the Virgina has a max speed of, hypothetically, 30 knots, then you will need to assign its Speednoise to 12.75 to give the SW and the Virginia equal noise at equal speeds.

DW is still the most up-to-date modern sub-simulator, so I'm still lurking from time to time checking for any new pet-projects, scenarios, etc, though with admittedly long stretches without checking in. There's hopefully a new player on the block coming though: http://www.warfaresims.com/

Sorry for resurrecting an older thread, but I wanted an understanding of how you came up with the thrust value of 12.75 for the virginia to equal the same for the seawolf at its max speed of 30 knots.

Based on what I understand you take your the speed noise per knot found under thrust dialogue and divide it by the max speed of the platform. 17/30 is 0.56 per knot for noise increase. What I want to know is how you reached the conclusion of the 12.75 for the thrust value of the platform to effectively match the seawolf at equal speeds until it passes the max speed of the virginia. I think I got the first part of it I'm just missing how you arrived at the new thrust value from the 17/30 to 0.56 per knot we started with.

Caveat: I never modded DW to test this out.

Afaiu(nderstand) the math, you take the max speed noise (maybe a typo on your part, but it is not "per knot", but total) and divide it by the max speed of the unit to get the speednoise per knot. So for the SW in that example is max speednoise/top speed=17/40 kts= 0.425 noise points per knot.

In order for the VA to be equally noisy at equal speed as the SW, the max soundnoise needs to be proportionally lower as the top speed is lower (30 kts). So 0.425x30 kts=12.75

Looking at it in a different way:12.75 speednoise points (VA) is 75% of 17 speednoise points (SW),
as is 30 kts (VA) being 75% of 40 kts (SW)