You really don't always need a "Lock" in auto-targeting. Make certain that you have your tubes doors open, and then point your scope or TBT at the target, and press the PK button. As soon as you can, press the Fire button. If you are between 500-800 yards away, especially if close to a 90° solution, you should hit the beast. You could "lead" the target toward the direction of travel, but still aiming at its hull. Be careful of oblique angles, especially if you have "duds" checked in the Options screen, because if the torpedo gyro has to turn too far, it might "circle-run" on you and come back like a boomerang...
Now, if you don't have the Steam version, you could try the
Silent Hunter 4 v1.4 update, and get slightly better game performance. However, your old Saves would not be compatible with it. If you have Steam, you have to purchase and use their Uboat Mission Addon package, which would take you to version 1.5, which is better.
