[Kapitan]

I think what you find is that the Russians went for speed in their submarines not so much stealth, the Americans went for lower speeds but more emphasis of being quiet.

If you look at the designs From the Thresher permit class forwards you notice this here is a submarines that has substantial speed of around 30 knots yet at the slow end they are a lot quieter than the Russian boats.

Prop design has a lot to do with this, if you look above the Romeo has twin 4 blade screws which would make a racket at any speed, and the counter rotating screws i don't think give much more quieting effect and likely cause pressure waves between the blades thus creating a slight noise increase in that area.

Americans / West have always tried to out do in terms of quality the Russians knew they couldn't match the tech platform to platform so created a wide range of measures to defeat the technology advances of the west.

None are more prevalent than a lone Project 877V Boat assigned to the black sea fleet in Sevastopol, here is a submarine that steps outside the idea of "good enough" and opens a new door the results of the trails are still classified the submarine is still active it was launched in 1990 and forms along side her newer and more advanced project 636 sisters the back bone of the submarine fleet in the black sea.

Alrosa is one of a kind submarine she is fitted with a pump jet propulsor almost like a mini jet engine if you would, its unclear how much noise reduction you get out of the modification but i would guess as they have not fitted it to newer boats or new builds including the Lada class that this trials boat wasn't too successful some pictures illustrate the system in bits and pieces.

























Taken from a screen grap but this is what type of screw the Project 877 and 636 boats have normally and infact still use