During a sea battle a target ring supports the player.
If properly most of the balls will miss the enemy vessel, the target ring will be red. In case of a green ring the current position is good enough to cause severe damage.
Under some circumstances, e.g. the wind comes from the right direction, it’s worth a try to volley in front of the nose of the vessel even though the target didn’t turn green yet. The enemy AI tries to follow your ship and such a maneuver can cause a broadside hit.