Yep really good info, not even used by ye olde salts all of the time
Regarding the range of the hydrophones, Buchheim's three photo books are a very good source of information. E.g. he states that theoretically you could see for 20 kilometers, but only in (very) favourable conditions. So it would be from 8-16 km in most conditions, 20 in very good and certainly none in fog.
The height of the boat (where you stand, with your binocs) is the limiting factor of course, but silhouettes od ships can be seen from very far away against the horizon, while the low boat's silhouette remains invisible against the horizon, looked at from the higher hull or bridge of a surface ship.
I still think the visible detection of the destroyers is much too good, also at night - they will fire at you without seeing you in dense fog, and also easily ram you in zero sighting conditions.
But will look for the newest mods, maybe there's some improvement.
Thanks Misha,
Catfish