Quick and dirty example. This is in effect the same diagram nisgeis posted.
Sub moves some distance in the period from observation 1 to 2. Let's say she's moving 5 knots.
The top target observed at bearing 280 in both cases has an AOB of 65. In the time interval of obs1 to obs2 she moves ~108% of the path length of the sub. That's 1.08*5 = 5.40 knots. This might well be ruled out by the sonarman's speed range.
The next target has an AOB of 35. Still at 280 on both bearings. So she must move ~174% of the sub's movement in the time period from obs1 to obs2. That means she has to go 8.7 knots. If the sonarman said 8-12 knots, this path is entirely possible.
The next has an AOB of 28. She'd have to move at 10.6 knots to keep the relationship. Still within the 8-12 as a valid solution.
Note that there are INFINITE solutions like this. Note also that all the above examples cross the sub's path at angles not equal to 90.
Greyrider's givens are 080/280 bearing. Closing target with sonarman speed range estimate. Submarine speed. All else is unknown. He seems to say that if it is possible to keep the target on 080 at >0 to max submerged speed, then the AOB must be 010, which, obviously, is nonsense.