I like to stay in the lanes as well. Assuming I have radar, I draw 20nm circles (~radar range) along the lane and follow the edges of the circles for my search pattern, back and forth on the surface up the shipping lane. That way I'm convering about a 40 mile swath of the path the ships are likely to take. Upon sighting I drop to "decks awash" depth (35 - 40 ft depending on waves, probably deeper than real depth as I am chest deep in salt water

) and plot course, speed and intercept (yah MOBO!

). Once the attack is planned, I get into position, going to scope depth as soon as possible, and listen on sonar. I like a Cromwell attack best if possible, and when the victim is within 5 - 10 degrees of shoot bearing, up scope, and it's fishies away!
I also like to shoot from stern to bow, The sequence is "Wait for juicy part to cross wire" [ENTER] (fire torps), W (next tube), [RIGHTorLEFTARROW] (move scope ahead a bit), rinse & repeat.
Thanks to you all here who helped me figure all that out!
Love this game! Love this (SUBSIM) community!