Hello, Ligne Maginot!
First of all, you should choose your area wisely before starting a new patrol unless you follow the randomly generated grid by the game. In stock version you get 500 renown for reaching it and an additional 200 renown for staying there for 24 hours. However, in GWX you get renown neither for reaching the grid nor patrolling it thus it's up to you where you go.
I suggest you take a look at the SH3_Map located in the
documentation folder at search after the grey areas like the Western Approaches and US Atlantic Coast. These waters usually abounds merchants so it's highly likely to find targets for your torpedoes.
When sailing for the grid I set my speed to Ahead 1/3 because it's the closest to the most economic speed and I don't change it after reaching the patrol grid either. En route you should dive for a hydrophone check at least twice a day for an hour or two especially in case of low visibility. When reaching your grid make your Navigator plot a search pattern. Now you can do more hydrophone check a day, it depends on you how many. If you don't see a single fishing boat after all after a couple of days, you might want to choose another grid.
IRL, it was completely different. U-boats were ordered to send patrol reports regularly and BdU always chose their patrol grids so captains had no freedom of manoeuvre.
Hope this helps a bit. Gute Jagd!
