Why don't you check out my very buried
U-Boat Fast-90 tutorial in the Advanced TDC/PK thread? No video yet, but I think the instructions will get you started. The Dick O'Kane technique in the same post works for U-Boats too.
The beauty of these two techniques is that range doesn't matter one bit in setting up your shot. You can even leave the range set to zero if you want. Don't try them unless you want to be deadly and have a lot of fun doing it.