Between two boats at an obstruction other than a mark where rule 18 applies between them. At a continuing obstruction rule 19 always applies and rule 18 does not.
Obstructions include moored boats, a shoreline you cannot cross, a no-go area the sailing instructions designate, and another boat you must keep clear of. Racing boats are only obstructions to boats that must keep clear of them.
19.1 When Rule 19 Applies
Use rule 19 at obstructions that are not marks, and at marks that are continuing obstructions. When boats are at a mark where rule 18 applies, rule 18 governs even if the mark is also an obstruction, and so does a third boat overlapped with both.
19.2 Giving Room at an Obstruction
(a) The right-of-way boat may choose to pass on either side. If she changes course to do so, she must give the other boat room to keep clear. Unlike a breach of rule 16, a breach of this requirement is not exonerated by rule 43.1(b).
(b) When boats are overlapped, the outside boat gives the inside boat room between her and the obstruction, unless she has been unable to do so since the overlap began.
(c) Along a continuing obstruction (a seawall, a long line of moored boats), a boat coming from clear astern that pushes into a gap that is not big enough at the moment the overlap begins gets no room, and has to keep clear for as long as the overlap lasts.
Common situations
Two boats approaching a moored yacht
Starboard (right of way) chooses to pass to leeward of the moored yacht; port, overlapped inside her, is owed room to pass. If starboard instead luffs to pass to windward, she must give port room to keep clear as she changes course.
Beating up a shoreline
Boats on the same tack approach a beach. The outside boat owes room to an inside overlapped boat to pass between her and the shore, but the inside boat must hail and tack under rule 20 if she needs to tack away.
Changed in 2025
Rule 19.2(a) now makes clear that "side" means the side of the boat, and adds the duty to give room to keep clear when the right-of-way boat changes course to choose her side. Continuing obstruction is now a defined term.