20.1 Hailing and Responding
When approaching an obstruction, a boat may hail for room to tack and avoid a boat on the same tack. However, she shall not hail if

(a) she can avoid the obstruction safely without making a substantial course change,
(b) she is sailing below close-hauled, or
(c) the obstruction is a mark and a boat that is fetching it would be required to respond and change course.

20.2 Responding
(a) After a boat hails, she shall give the hailed boat time to respond.
(b) The hailed boat shall respond even if the hail breaks rule 20.1.
(c) The hailed boat shall respond either by tacking as soon as possible, or by immediately replying ‘You tack’ and then giving the hailing boat room to tack and avoid her.
(d) When the hailed boat responds, the hailing boat shall tack as soon as possible.
(e) From the time a boat hails until she has tacked and avoided the hailed boat, rule 18.2 does not apply between them .

20.3 Passing On a Hail to an Additional Boat
When a boat has been hailed for room to tack and she intends to respond by tacking, she may hail another boat on the same tack for room to tack and avoid her. She may hail even if her hail does not meet the conditions of rule 20.1. Rule 20.2 applies between her and the boat she hails.