assigned grid vs. convoy attack

Ahoy!
I wonder real U-boats how many attacks performed one after one on a given convoy. I suppose remaining torpedoes, fuel and damage and weather were the key factors but apart from this did they keep attacking till they ran out of eels then exit chasing and return to base?
I'm asking it because on my current patrol with a VIIB in June 1940 I was heading for my designated grid by the Azores, when spotted an enemy convoy SW of Ireland. After an attack 9 eels remained. Should I ignore the assigned patrol grid and attack again and again or set course to the original destination letting the convoy sail away perhaps into the hands of another U-boat.