Your diagram adds an interesting scenario to this question.
Let's assume yellow has entered the circle on starboard, but is not quite fetching the mark.
Let's say blue is not there and yellow must pinch up and briefly go above close-hauled to clear the mark.
Now with blue in the picture, can yellow claim blue caused her to go above close hauled to avoid contact, thereby penalizing blue?

Both boats tacked in the zone. RRS 18.3 says"If A boat passes head to wind. IMO RRS18.2(c) When 18.2(a) does not apply and the boats are overlapped the outside boat seal give the inside boat mark room. 

Hans, you're right, rule 18.3 has a substantive change in 2025, at a starboard-rounding mark when both boats tank to starboard in the zone and one of them is fetching the mark.  Under the current rule, if a boat tacks to starboard just inside the zone and then another boat crashes in, tacking to starboard right at the mark, the tacking boat gets mark-room as soon as she passed head to wind, meaning she's exonerated if she breaks rule 13 and, after her tack is complete, rules 15 and 16.1 (if, for example, she shoots the mark).  This did not seem like a good thing, and now the tacking boat will have to obey those rules or take a penalty. 

I don't understand your statement that there is a 'conflict' between new rules 18.2(b) and 18.3.  In the scenario you describe, rule 18.3 says 'rule 18.2 does not apply.'. Rule 18.2(c) is part of rule 18.2, so it doesn't apply. Hence, no conflict.

Rob my problem is that rule 18.2(b) and 18.3 both apply in the situation in my diagram - as I read the rules.
So which of the rules should we use - 18.2(b) give Mark-room to B and 18.3 do not ?

18.3 Does not apply to the above scenario because Y was not on starboard tack when she entered the zone.  Y is not on starboard until passing head to wind at position 5. 

There is a lot going on with this diagram, and maybe a few open questions.
I assume this diagram describes a port rounding.

Under the 2025-28 rules, mark room is established at position 3.5, but then is turned off by RRS 18.2(b) when blue passes head to wind while starting to tack at position 5.1

To me, it looks like, at position 5.1 through 6,  yellow likely tacked from port to starboard too close to blue and possibly forced blue to tack to avoid contact.  At position 4, it does not look like there is enough space for yellow to tack and remain clear of blue during the tack.  As drawn, I think it reasonable that blue should have been able to sail to its starboard tack layline before it (blue) tacks to starboard, and that yellow would need to stay clear of blue through all this.  (Note, the diagonal grid lines on the drawing indicate to me the lay lines as well as the heading needed to establish a close-hauled course.)

So, to me, an issue is that the diagram shows that neither boat has established itself on starboard tack.  So, are they are both still tacking, and just luffing their way to the mark?  I think RRS-13 governs this and blue needs to stay clear of yellow when both are tacking at the same time

However, if blue somewhere in this sequence established herself on a starboard tack heading and thus becomes leeward of yellow with luffing rights, then blue "just" needs to avoid the mark and has the right to pinch/luff up around the mark, and yellow (windward) would need to stay clear.

While RRS 18.2(c) requires the outside boat (yellow) to give mark room to blue, it seems the whole 18.2 rule is turned off by RRS 18.3 when blue tacks.

So, bottom line, it seems to me that there is no mark room (for blue) in effect after position 5.1.  If blue established (for an instant) a close-hauled course on starboard tack, then she can luff yellow and get around the mark.  Otherwise, by RRS 13, yellow has the right to fall off to close-hauled starboard tack, which would effectively block blue's path to the mark, unless and until blue somehow establishes starboard tack with luffing rights.  Yellow needs to avoid contact with blue at all costs, but be ready with its protest flag.

Hans ... maybe it'd be clearer to step through your scenario position by position. 

The above ignores the issue of tacking too close and rule 13 issues at play.  Just focusing on MR, which I think was the issue in Han's mind. 

PS: it does not matter in this scenario which boat passes HTW inside the zone before the other, or if they do so simultaneously .. it works out the same as long as they both pass HTW inside the zone. 

James re: "18.3 Does not apply to the above scenario because Y was not on starboard tack when she entered the zone."

First, please be sure you are looking at the new 2025-2028 quad, the wording is different.  In the new quad, RRS 18.3 definitely does apply.  That is an important point because it is 18.3 which turns off 18.2 (and thus 18.2(c) MR).   

18.3 does not apply until Blue passes HTW. For more detail please see my comment above this one. 

Thank you Angelo - as you write I only focus on RRS 18.

I - almost agree with your comments, but;

1) Between pos. 5 and 6 B and Y are on separate tacks - RRS 18.1(a)(1) apply (same in present RRS) - RRS 18 do not apply - no Mark Room to B.

2) Between pos. 5 and 6 B (boat entitled to MR) passes HTW - RRS18.2(b) apply and stop 18.2(a) but  not 18.2(c) - B entitled to MR (same as present RRS 18.2(d) stop (b) and (c) but not (a)) - B entitled to MR. (present and new RRS).

Present RRS never activate RRS 18.3.

New RRS;

3) Between pos. 5 and 6 B tack to Stb. and Y can fetch the mark - RRS 18.3 apply and stop RRS 18 - no MR to B.

This because the 18.2 cutoff has been moved up in the 1st sentence, before the additional "if-scenario").

For me we now have 3 RRS applicable for pos.5 to 6.
Two of them stop RRS 18 (18.1(a)(1) and 18.3) - no MR to B
RRS 18.2(b) only stop  RRS 18(a), 18.2(c) still apply - MR to B

So why is it you apply 18.3 in the situation and not 18.2(c) ?

Thsi is what I meant with conflict between 18.2(b) and 18.3

Hans I will insert my comments within yours below to make our conversation more clear.  I won't comment on the current quad and only focus on 2025. 

RRS 18 does not stop when 18.3 applies, but 18.2(a) is stoped. Maybe that was a typo?

Rule 18 in its entirety turned off when Y passed HTW before B did.  The boats are on opposite tacks on a beat to weather so 18.1(a) disables 18 which includes 18.2(a). 

When B passes HTW after Y, 18 turns back on as they are both in the zone, on the same STB tack and none of 18.1 exclusion conditions are satisfied. 

 18.3's test is satisfied and is the rule activated, which excludes all of 18.2. 

Since Y did not enter the zone on STB, neither 18.3(a) or (b) apply. 

So, 18.3 applies but the MR in 18.3(b) is unavailable. 18.3 turns off 18.2, so all MR under 18.2 is also unavailable. 

Art,

By definition, if yellow is able to clear the mark by pinching above close-hauled, she would be fetching the mark.  If she were "not quite fetching the mark", she would need to pass head-to-wind to clear the mark to port.

Hi Angelo - I do not think it was a typo - if RRS 18.3 apply 18.2 do not.

I think we both agree on how the new rules work - my problem is why the scenario betweeen pos. 5 and 6 end in RRS 18.3 - it could also end in 18.2(b/c) ?
The checks for applying both RRS 18.2(b/c) and 18.3 are fulfilled ?

Like Rob said, submission E07-24 is a quite significant change to the current rule 18.3. The change is just not highlighted in the submission, so it's easy to miss...  Good that Hans mentioned this here as well, so we are more on the same page. 

I don't see 18.2 and 18.3 as conflicting. 18.2(c) still gives mark-room to the inside boat, if they are leaving the mark to starboard. 18.3 is talking about this specific case that Hans drew up there, and tells that in this case 18.2 doesn't apply. 

And thanks Angelo for making the argument that it doesn't matter, who passes HTW first! I was initially reading it so that 18.2 wouldn't apply only between the tacking boat and a boat that was on starboard at the time of the tack. This would have created a royal mess of figuring out, who was first to go, and depending on that, if the MR was there, or not :D 

OK all.
My conclusion:
If the (top)mark are to be left to port - 18.3.
if not 18.2(b/c).
And happy new year to all !

Juuso re: "And thanks Angelo for making the argument that it doesn't matter, who passes HTW first! I was initially reading it so that 18.2 wouldn't apply only between the tacking boat and a boat that was on starboard at the time of the tack."

Yea .. it works out all 3 ways:

At one point, I thought there was a problem in #3, but I got straightened out with a little help from my friends (you know who u are lol).