Section C has been completely rewritten and split into three rules: 18 -Markroom, 19 - Room to pass an obstruction and 20 - Room to Tack at an Obstruction
The preamble of part C covers all of them:
AT MARKS AND OBSTRUCTIONS
To the extent that a Section C rule conflicts with a rule in Section A or B, the Section C rule takes precedence.
Section C rules do 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. When rule 20 applies, rules 18 and 19 do not.
18 ROUNDING AND PASSING MARKS AND OBSTRUCTIONS In rule 18, room is room for an inside boat to round or pass between an outside boat and a mark or obstruction, including room to tack or gybe when either is a normal part of the manoeuvre. 18.1 When This Rule Applies Rule 18 applies when boats are about to round or pass a mark they are required to leave on the same side, or an obstruction on the same side, until they have passed it. However, it does not apply (a) at a starting mark surrounded by navigable water or at its
anchor line from the time the boats are approaching them to start until they have passed them,
or (b) while the boats are on opposite tacks, either on a beat to windward or when the proper course for one of them, but not both,
to round or pass the mark or obstruction is to tack
AT A MARK-ROOM
18.1 When Rule 18 Applies
Rule 18 applies between boats when they are required to leave a mark on the same side and at least one of them is in the zone. However, it does not apply
(a) between boats on opposite tacks on a beat to windward,
(b) between boats on opposite tacks when the proper course at the mark for one but not both of them is to tack,
(c) between a boat approaching a mark and one leaving it, or
(d) if the mark is a continuing obstruction, in which case rule 19 applies.
The rewriting of rule 18 is not so much a change, as to bring it into a more logical an structured order, so that the rule is better understood.
Note that the "about to round" part has been dropped and that one of the boats has to be in the zone, before rule 18 kicks in.
No more rule 18 outside that zone, only the other r.o.w. rules. And before you ask about conflicts with rules in part A and B (inside the zone); that is dealt with in 18.5.
We will have to see on the water what specific impact this will have.