This descision depends on a lot of variables.
- Whats the type of sub you are hunting (loud/silent ...)?
- How fast are the Helos on station?
- How much time do the buoys take to start to send?
- What are the Sonar Conditions in the area?
- How "sensible" are the buoys?
- Is the sub expected to take a certain course or just "hang out" in the area?
- How large is the area where the sub might be (which in turn depends on the speed of the sub for starters)?
- Can you expand all buoys on this target or do you need to conserve your buoys?
Those are just a few questions of the top of my head who influence the way I would deploy the buoys. Sometimes you have to drop a circle (or sort of a circle), sometimes a semicircle or even a barrier works. The spacing might be wide because of good sonar conditions and a loud sub or it might be tight because of the opposite situation. You might only have enough buoys to cover one barrier with a useful spacing and maybe have to alternate depth too.
In the best of worlds you know how fast the sub is heading somewhere and can place a neat little barrier or "detection circle" in its path. Unfortunatly ASW is still most of the time deep in the realm of the SWAGs (Scientific Wild Ass Guesses).
Tho thats just my 2cts ... SQ might see things differently.