Look, after reading the range twice with the stadimeter, the clock icon gives you speed and course ok?, now then drag the aob dial (up right) so the other aob dial in the PK matches the course of the target (outer dial).
Its far more easier to attack multiple ships now, after shoting the first target, lock the second one, adjust aob, get range and fire!.
I made a video for you from the torpedoes training mission:
Note how the aob dial in the PK moves.