Sonar experts: How much sound crosses a layer?

[OKO]

The situation you describe would occur if there is a minimum amount of machinery noise that CAN'T be reduced even at stop (why?)

it's a fact known for all nukes
even at complete stop they still make noise, and there is very few difference beetween a nuke at stop and a nuke at 5 or 7 knts

But I don't think you get my point :
As I told you, there is always, on every hull, a time where you start creating hydrodynamical perturbations, when the laminar flow start to become not so laminar, and here turbulence are created.
As I told you, I could see that each time I go sailing, on the rear of my boat.
that's because my hulls (its a multihull) are optimised for cruise at 10 to 11 knts.
If I go over this speed, even if I could go much faster (well ... its still a sailing boat anyway ...) I will have much more turbulence in my wakes.
but before 10 knts, if you look at the wakes, you have the impression that the ship is stopped
and suddenly, if you go over that speed, you see wakes coming.
It's the time the hydrodynamical flow stop to be absolutly laminar along my hulls.
Not only this slowly brake the increase of speed, but also from this point, I start to need more energy (from the wind) to increase the speed than I needed before 10 knts.
Just because I've got out of the optimal flow, starting turbulence.
And turbulence for subs is noise.

So, for subs, there is also a critical point like this.
A point where a real commander will know he will produce much more noise.
And this is an important tactical thing.
Tactical thing that doesn't exist at this time in DW, but existed in stock DW, as the screens above could show you