By November, you might as well give up on the idea of taking out a whole convoy
Convoys get quite large and usually well escorted out there.
If you find you're missing the second target because the convoy is pulling hard left/right to evade torpedoes, try timing your attack better. What I mean by that is time the shots so your four front tubes all hit around the same time.
Take the longest shot first - whichever is furthest away. When you've got two fish heading for the more distant target (say 2000yds), wait until the torps are halfway there or so, then fire the remaining two at a closer target (at say 1000 yds).
Experiment with torpedo speeds to help time detonations close together - this gives them no time to evade and makes sure your first salvo does as much damage as possible. If you can, swing the boat around and get off a shot with the bow tube(s), then get deep and quiet. If you slip away, you can go high speed to get in front of the convoy again (depending on weather/time of day etc) for another attack.
Good hunting!
