See if you can use the remaining night to position your self out in front of the CV and about 1500-2000meters to one side of the lead escort (usualy one sails in front marking the center of the CV nicely.
If your patient stay in that position stalking untill the next nightfall.
For the attack i would go into the convoys outer and nextouter lane and shoot at the center lanes. Then i'd submerge to about 20 meters and try to dissappear to the side im placed in. Fire 4 torpedoes from the front - turn for about 125 deg. and shoot the rear torpedo (roughly the escape axis as well). when your out of the convoy and at about 2000-2500 meters from the nearest DD's (dark clouded night) surface and step on the pedal utill your at about 7000 meters (or what ever your visual range is) then setup another stalking/overtake/attack procedure.
To me it seems that DD's will have a harder time to pick you up near the surface, even decks awash sometimes works better for me then submerged. Had a DD pass me at roughly 100 meters the other day - never saw me (mind i never saw him either as i was watching a shot at a target on the other side. I had not noticed that DD prior to shooting
). I was totally baffled with that he never noticed me
What ever you decide remember Section I. D # 79 in the U-boat Commander's Handbook
"If operations are carried out at depth of 20m and less, the loss of the submarine must be reckoned with, once it has been detected. But in such cases also, as has been demonstrated by the experience gained in wartime, difficult situations due to pursuit by the enemy may well be mastered, if the commander acts cleverly and coolly, and the crew remains steadfast. (U9 in the spring of 1940, U123 and U333 in the spring of 1942)"