Thanks for the fast answering.
I find it's in near all situations impossible to catch a map convoy in silent running speed (I think 3 knots).
That's a real gamebreaker for me because you have to approach the convoy for at least visual contact in 1 time compression and at silent running speed. Sure 2 hours in order to get a succes position

.
The problem is that in near all attemps I get detected at very long distances (more than 20 km) when I approach the convoy path. They seem to mark my position in the map and start zaging when they get into visual distance.
I'm good in vector maths and single merchants are doomed when I get their map or sonar contacts, but convoys always zig-zag after a time compression approach-and-waiting strategy. Do you find the same problem?
Is there any mod where you can turn on/off the AI sonar detection?