About the mousewheel: Sorry Effigy, you allready said that. Note to self: Read before posting!
In my experience, when I am on a position 90 degrees to the target's course, and waiting for it to close in on my bow, their zig-zagging doesn't do much to evade their doom. Definately not when I've got fast torpedos. It slows them down a bit but the side of their hull will embrace my torpedos gladly. Their zig-zagging may get them too close to you to fire though, if you placed yourself 'up close and personal' (minimal torpedo arming distance).
As for doing things quick: Try not to shoot at destroyers or other baddies with a vengeance, especially when they are allready on to you. It's like swatting flies in mid air. They're too quick and agile. Diving and making low noise is your best defense.
And there are ways to seperate the measurements of speed and determining course/AOB. Also it's best to prepare these measurements well before shooting. IE, if you can ID a ship, you can let the length of the target show his speed by the time it takes to pass. Turn you scope (AND bow) right before his so he is about to pass through the scopeline, and time the passage. A bit of meter/second/knot-number juggling and presto, his speed. If you take bearings and distances at regular time, you can plot those on the map based on your boat's positions. That shows you the direction he's going. And based on where you are compared to him (assuming you placed yourself atr a good position) shows you the angle on his bow (AOB). Which remains good (and updated by TDC) as long as you do not turn your boat afterwards. Then just before firing time you can do another range check and enter that into the TDC. But this is hardly neccessary if the target is distant. Only important for close shots, and large gyro angles. (just make sure it's ballpark-ish for distant shots)
This is just a short summery of other techniques. There are threads in the forum that are more elaborate on a specific technique. But, to also add my advertisement
, it's all neatly done with OLC's Gui mod (Ubermod or not). IM(not so)HO