Thanks for all the answers. I indeed joined in 2014 but started contributing only recently. Played some GWX SH3 earlier as well (still think it's the best) and now some SH4 with TMO.
Also the Dick O Kane -method is quite good (it's all about vectors) but very inflexible against convoys since it relies on you being in a straight angle, and thus if the ships are in column you have to wait for the next ship in line to cross over which takes time (on the other hand the usual way of identifying and stadimeter takes time as well so pick your poison I guess!).
But at least in my game the weather is so bad so often that I pretty much have to use often only sonar to launch torpedoes. I guess it's possible, you just need to be very quick listening when the ship is on correct bearing. Once close enough the window to launch torps is very small.
I take it that the loudest sonar bearing will be directly from the engine room, i.e. from the very back of the ship so you need to shoot a little bit in front of the loudest sound?
Also I had a lot of problems with the game crashing periodically and found out it was due to insufficient memory allocation to the game. I digged up the forums and found this 4GB memory patch which I applied to sh4.exe. The game so far hasn't crashed once (fingers crossed)! And it doesn't lag either when the game loads up something. It can potentially make the game function better generally as well, helping keep track of all the stuff it has to spawn.
https://ntcore.com/?page_id=371