Hmm i get the feeling your not getting it. Your course, speed, etc meens nothing in determining angle on bow. Angle on bow is a mesurement of the bearing to your uboat from the perspective of the target ship. Here ill give you some more picture examples
Code:
X Target Ship
|
O your Uboat
|
Both you and the target are going north, AoB is 180
Code:
X Target ship
|
|
O your Uboat
Target is still going north, your now going south, AoB is still 180
Ill say it again, imagine your on the bridge of the ship your targeting, looking out on your uboat, the angle from the bow of the target ship to the direction of your uboat. Is the AoB
Some more examples just to be sure you got it

in the following 3 examples the target ship is going east past your position and your facing north
Code:
--X Target ship
O your uboat
|
The AoB for this example is roughly 45 degrees right
Code:
--X Target ship
O your uboat
|
The AoB for this example is roughly 90 degrees right
Code:
--X Target ship
O your uboat
|
The AoB for this example is roughly 135 degrees right