As far as manual targeting simplified goes, I found that the information in the following link to be spot on:
http://www.subsim.com/radioroom/show...6&postcount=67
Fast 90 U-boat targeting
Does exactly what it says. Only time I have missed firing across the track of a convoy at a merchant on the far side, was because I failed to open the bow doors before firing, so my torpedo passed astern.
Works like a charm when firing at multiple targets in quick succession.