Well guys, first off let me say thanks for the comments.
Secondly, not to worry, from the first attempt I fell in love with this targeting technique, and thanks to my problems listed above, have become quite proficient in using it while trying to rectify why my torps were not exploding. Nonetheless, last night was a successful night of ship sinking thanks to the tutorial video (thanks RR

) and the Dick O'Kane technique. I fired LOTS of fish last night, and had LOTS O' hits. What I did while waiting on replies to my first post was set my fish to run as shallow as possible, and then to also ensure than my torps were impacting at slightly less than or more than 90 degrees. Success! And, it turns out, those are exactly the things you all ended up recommending above, so that only proves I asked the right folks for help. Sounds like a win win situation.
Again thanks everyone, and here's to many more happy sinkings thanks to this particular manual targeting technique.