I just try to park my sub in the middle of a shipping lane, submerge the boat to radardepth and up the TC untill I get a sonar/radar/visual contact and move to engage. Works fine, but it is a fact that the sonarguy is completely incapable. Sonar has (theoretically) the longest detection range, but I often make contact with the radar first. Sometimes even visual, proving that the radarguy is just as incapable.
When I listen myself, I can hear contacts the AI did not detect. Likewise, if I look at the radar screen, I can see contacts the AI did not detect. If I'm desperate for a contact, I take a listen myself every 2 or 4 hours, on the hour. But I'm usually not that desperate.