When a boat approaching an obstruction hails for room to tack, but does so before the time when she needs to begin the process described in rule 20 to avoid the obstruction safely, she breaks rule 20.1(a). However, even if the hail breaks rule 20.1(a), the hailed boat must respond. An inside overlapped boat is entitled to room between the outside boat and an obstruction under rule 19.2(b) even though she has tacked into the inside overlapping position.