It is quite a bit more realistic with the WoS mod with Real Nav enabled - no map contacts display - even radio contacts (which annoys me).
What I do is just sail to my patrol grid and after satisfyiing those requirements I sail around known shipping areas. I generally do not bother with hydrophone searches unless I notice the TC start to chug.
That's your clue that something is nearby.
But generally I rely on visual contacts.
However, your radio operator will report "nearby" contacts. This is different from with map contacts on where you get ALL of the contacts and you can easily plot intercepts from across the map. Instead you will only get nearby contacts and then you have to plot where they are and generally what direction they are going in and try to plot an intercept. I have about a 50% success rate in intercepting in this way. Other times they get away.
You can assign promotion points to your radio operator that is supposed to increase his ability to report contacts - I don't know if that has been nerfed in WoS or not.
My tonnage is greatly reduced since going 100% realism WoS. Some patrols I only get 2-3 ships. If I hit a convoy I might get 5-9 ships in a patrol.
But, it's only 1941, and I can still get away with short-range convoy attacks from within the convoy. After 1942 you had best start with 5000m hail mary attacks from 5000m away from the nearest escort or you are doomed. In this case slow-speed steam FAT torpedoes are your friend.
Steve