Welcome to subsim Herr Kaluen sasquatch!!!
Are you new to Subims at all?
If you are you must always keep one thing in your mind,, your out there, alone and faceing the Navies of Several Countries at once (well in the middle stages of the war to the end at least) your baseicly the blue dot in a whole sea of red, and all that red is looking for you, whether it be Planes, Destroyer hunter kill groups or random independand sailors and convoys.
You must always take it slow, to the point of staying under the water for all the daylight hours late in the war because of Aircraft attacks, and to always remember that somewhere, at anytime, A Destroyer has you on Radar.
I recommend getting the GWX Super mod (currently version 1.3) once you learn the ropes in stock Silent hunter 3, GWX makes the world a much more liveing breathing wartime place in the game.
Not to mention AI upgrades that will allow you to increase in skill and cunning alot faster then the sleepy in comparison stock AI.