Shadow the convoy at the edge of visual range (15km unlimited visibility, 10 km moderate, 5km reduced) and determine its course and speed. Overtake it and take position ahead and to the flank of it, 1-2 km from the track of closest column). Beware of the flanking destroyer. If it's early in the war you can attack surfaced at night.
It's not very helpfull to have different speed torpedoes in your tubes. You have to carefuly calculate time for each impact, in order to achieve all impacts more-less simultaneously. If not, the ships zig-zag and you miss.
Fire two torpedoes at two biggest ships, and dive. Once (if
) you escape destroyers, move away from the convoy to a safe distance, surface, and start all over again.
Remember that the convoy changes course for about 45-90 degrees each 50-100 km.
Good hunting
