I probably gave a confusing answer unitentionally. I meant that AOB is 90º when you are perpendicular to the target, not only to the target's course. What I meant is if you have the target right in front (Bearing 0 for you) and he is heading perpendicular to you, either left of right, then the AOB is exactly 90.
For all other situations, do what follows:
1.- Draw a triangle where one corner is your sub, the second the enemy vessel and the third is where your course and the target's course meet (X point in the scheme below).
X----------<======> TARGET (Heading left here)
I
I
I
I
I
I
I
U-BOOT (Heading up here)
Angle 1 is the one that goes from you 0 bearing to the target bearing (Approx 45º in this case).
Angle 2 is the one that goes from your course to the target's course (90º in this case, at meetpoint "X").
Angle 3 is the one that goes from the target's course to the target bearing of your sub. That is the AOB.
Now, because in every triangle the sum of all its angles is ALWAYS 180º, and because you know the value of two of the angles (45º from your bearing to target and 90º from having your course perpendicular to the target's course), then 180-90-45= 45. The AOB in this case is 45º
Hope that clarifies it all a bit more.
What makes it so confusing is that everyone seems to be using the AOB for exactly the opposite purpose it was created. :hmm: The AOB used because when being at sea level in your UBoot and first spotting a target, the only way you have to figure out where it is heading to (The course) was guesstimating how much left or right from a direct collision course with you was the target heading. Once time goes by and more observations have been done, the AOB becomes irrelevant as you have now enough stuff to plot the real target course, which is what in fact is of interest for you, and not the dreaded AOB.
But since the SH3 TDC works exactly the opposite as the german historic TDC (In which you entered target's course, and not the AOB, that changes constantly) people in the forum have ended up building up wrong procedures for manual targeting, which fit to the game's limitations, but not to historical reality. Such is life.