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20  Room to Tack at an Obstruction
20.1 Hailing
A boat may hail for room to tack and avoid a boat on the same tack. However, she shall not hail unless
(a) she is approaching an obstruction and will soon need to make a substantial course change to avoid it safely, and
(b) she is sailing close-hauled or above.
In addition, she shall not hail if the obstruction is a mark and a boat that is fetching it would be required to change course as a result of the hail.

20.2  Responding
(a) After a boat hails, she shall give a hailed boat time to respond.
(b) A hailed boat shall respond even if the hail breaks rule 20.1.
(c) A 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 a 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 a 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 a boat she hails.

20.4 Additional Requirements for Hails
(a) When conditions are such that a hail may not be heard, the boat shall also make a signal that clearly indicates her need for room to tack or her response.
(b) The notice of race may specify an alternative communication for a boat to indicate her need for room to tack or her response, and require boats to use it.

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