Rule 19 is completely new and splits off obstructions from the "old"rule 18:
19 ROOM TO PASS AN OBSTRUCTION
19.1 When Rule 19 Applies
Rule 19 applies between boats at an obstruction except when it is also a mark the boats are required to leave on the same side. However, at a continuing obstruction, rule 19 always applies and rule 18 does not.
19.2 Giving Room at an Obstruction
(a) A right-of-way boat may choose to pass an obstruction on
(b) When boats are overlapped, the outside boat shall give the inside boat room between her and the obstruction, unless she has been unable to do so from the time the overlap began.
(c) While boats are passing a continuing obstruction, if a boat that was clear astern and required to keep clear becomes overlapped between the other boat and the obstruction and, at the moment the overlap begins, there is not room for her to pass between them, she is not entitled to room under rule 19.2(b). While the boats remain overlapped, she shall keep clear and rules 10 and 11 do not apply.
Subsequently all following rules have been renumbered:
20 ROOM TO TACK AT AN OBSTRUCTION
20.1 Hailing and Responding
When approaching an obstruction, a boat sailing close-hauled or above may hail for room to tack and avoid another boat on the same tack.
However, she shall not hail unless safety requires her to make a substantial course change to avoid the obstruction. Before tacking she shall give the hailed boat time to respond. The hailed boat shall respond by either After a boat hails,
tacking as soon as possible, in which case the hailing boat shall also tack as soon as possible, or she shall give the hailed boat time to respond;
immediately replying ‘You tack’, in which case the hailing boat shall tack as soon as possible and the hailed boat shall give room, and rules 10 and 13 do not apply. 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; and
(c) when the hailed boat responds, the hailing boat shall tack as soon as possible.
When a boat is taking room to which she is entitled under rule 20.1(b), she shall be exonerated if she breaks a rule of Section A or rule 15 or 16.
20.3 When Not to Hail
A boat shall not hail unless safety requires her to make a substantial course change to avoid the obstruction. Also, she shall not hail if the obstruction is a mark that the hailed boat is fetching.
19.2 Rule 19.1 does not apply at a starting mark surrounded by navigable water or at its anchor line from the time boats are approaching them to start until they have passed them or at a mark that the hailed boat can fetch. When rule 19.1 applies, rule 18 does not.
The rewriting is again done to get a more logical sequence;
Obstructions: How the rules work when passing one, then the rule when you need to tack for one.
I've been thinking about the deletion of 19.2 especially the part about not applying at a starting mark when boats are approaching to start. That has not been rewritten in the new rules.
That means that a tiny part of what was not allowed in the old rules has been deleted: If you approach a starting mark on starboard, which is also an obstruction - say a pin-end Race Committee vessel - you can hail. But only if the hailed (windward) boat is NOT fetching the (committee boat)mark. You must give the windward boat time to respond - including time to hail other windward boats.
What if there's a three boat situation where the two leeward boats cannot fetch the pin-end committee boat, but the most windward boat can?
In my opinion the leeward boat cannot force the middle boat to tack, she can only luf head-to-wind. What do you think?