Mark, to answer this question, I have 2 Q’s:

1) under which quad?
2) where/in what direction is next mark?

Ang

PS: We had a very similar scenario/thread. I’ll try to find it (or someone else will post). 

Blue is now simply windward boat and would have to stay clear if yellow luffs. The mark room and the overlap are no longer relevant. 

Similar scenario/thread:

https://www.racingrulesofsailing.org/posts/274-contradiction-in-rule-18

Rob Overton ... wanna explain how this type of scenario lead to a change in rule 18 in the next quad?

At P1 Y is ROW, B is KC (R12). At P2 Y is ROW, B is KC (R12). At P3 Y is ROW, B is KC (R11).
At zone edge, B does not have Mark Room. Y has Mark-Room and is entitled to round the Mark (definition Mark-Room). B is not entitled to Mark Room (R18.2b). B has no right to go inside Y. 
R16.1 does not apply to Y's change of course since Y is entitled to "room to round the mark as necessary to sail the course". B can easily KC by sailing past Y's stern and the Mark. 
B has no right to round inside Y.

I would suggest that the luff by yellow probably broke RRS 16.  Blue is entitled to go in at her own risk, but yellow is constrained by 16 from "violently shutting the door"  - she must give the blue boat room to keep clear.
Interestingly, I have just been watching an RYA video making the same point - will post as a separate thread next.

I must be missing something. Y has made a classic "tight/wide" turn allowing room for a boat that has done a "wide/tight" turn to pass. Seems to me this is done all the time. Can someone explain what I am missing?  Ahh, I see Nick answered just about the same time as I did. That is what I was thinking, thank you.

Just to clarify.
The next Mark is 4 miles to windward

Mark,
Here is the Conclusion from Case 63:

This should clear things up a bit.
Kim

Thank you all for the insights. Very clear.
I shall pass this along to the skippers.

I think that rule 18.2(c)(2) is particularly relevant here:
"(c) When a boat is required to give mark-room by rule 18.2(b),
(1) she shall continue to do so even if later an overlap is broken or a new overlap begins;
(2) if she becomes overlapped inside the boat entitled to mark-room, she shall also give that boat room to sail her  proper course while they remain overlapped."
So when Yellow turned, Blue was required to give her room to sail her close-hauled course. If Yellow sails above close-hauled, she is sailing outside the room to which she is entitled under this rule.
Blue is not entitled to mark-room at any time in this incident and it looks like a close call for Blue. She was probably well advised to pass astern of Yellow.

Clark, I'd suggest that proper course would allow Y to sail above close hauled up to htw - if she can justify (e.g. to use her momentum - speed persisting from the run- to gain some way to windward)?
Since they are leaving the Mark, R11 applies and then Y can luff above close hauled (up to htw) - subject to R16.1 - unless B calls for Room at the obstruction (the mark buoy) and in that case, R18 still applies.

I agree with Clark.  Blue has no rights in this scenario inside the circle.  If Yellow left the door so wide open that Blue could sneak in there without impacting yellows course to the next mark - a high risk move - Blue could do it, but that is not the situation.  Yellow hardened up well within the circle and Blue is obligated to stay clear.  

Stewart:
An interesting theory as to Yellow's proper course. It would be an interesting bit of protest committee testimony for Yellow to sell that rationale. Is that commonly done in this type of boat? Would you (Yellow) have sailed above close-hauled in the absence of Blue? I think I'd be skeptical. especially since such an abrupt turn would more drastically slow the boat and cost more time than any compensating gain in distance.
That being said, let's see that the other forum participants have to say.

Clark, I now sail RC yachts - IOM - and it is common (or at least I do it) to turn from run to beat beyond close hauled to gain some upwind benefit. The IOMs carry their way well.

See also the following thread Rule 18 2021-24.

The Two Daves, Dave Perry and David Dellenbaugh, covered this multiple times in their webinars.
The boat with mark room can go as wide as she wishes and turn up. 
The criterion is whether at the time of encounter she was taking the room to which she was entitled under the rule.
Even if indeed 16 applies, the answer to the original question is 
   No. Blue is not entitled to room here.
Yellow would be smarter to avoid contact and protest Blue.

Philip,
The following comments are based on the rules from 2021.
I agree that Blue is not entitled to mark-room. The question, to me, is whether or not Yellow is still entitled to mark-room.
I contend that, from January, that after mark-room has been given  rule 18 no longer applies.
If this is applied to the above scenario I  believe mark-room has been given at position 2 as the two requirements in the definition of mark-room have been complied with. Yellow then becomes subject to other part 2 rules, in particular rule 16, and when she changes course she has to give room (  ...including space for a boat to comply with her obligations under the rules of part 2 and rule 31)  for Blue to keep clear.  Therefore part of the room that Yellow needs to give under rule 16 includes space for Blue to avoid the mark. 
I agree Yellow's best course of action is to avoid contact and protest but that the outcome of the protest may be different between the current rules and the new rules as under the current rules 18 would still apply but it won't under the new rules.
I appreciate others do not necessarily agree with my view and do think some further official guidance, by way of a Case, would be helpful. 

John Stanley,
I agree with your assessment under the new RRS.  At point 2 Y is no longer overlapped with the mark because they sailed past it and are over 1/2 of a  boat length away. I believe that under the new rules Rule 18 no longer in effect.  The positions shown in the drawing seem impossible for them to change in the relation to each other, but the other rules of part 2 apply.

Philip,
Let's stay with the current book and Cases.
Above, I posted the Conclusion of Case 63. Check it out.
As far as the new book goes, we will have to wait and see if WS will change the Case to reflect the 'new' rule.
Kim
 

Sorry John, this should have been addressed to John and Lloyd.
Kim

I think Stewart Campbell has a point.
I too race RC boats, we abide by the same rules as 'the big boats'.
Doing this has its disadvantages however.
The type of scenario shown above is quite common.
Firstly - not being in the boat creates problems.
A skippers ability to accurately calculate the position of their boat in relation to the mark when it may be as much as 100yds away causes any number of overshoots as with Yellow at postion 2.
Secondly scale models are faster across the water than a scaled down version of the full sized craft would be.
Thirdly RC boats can change direction very quickly.
Incidents such as this one can start and finish in a matter of a few seconds.
It is very difficult sometimes to come to a conclusion who was right or wrong! 

John Standley raises an interesting question. In the 2021-2024 Racing Rules of Sailing the definition of mark-room and rule 18.1 have been changed by submissions 138-18 and 131-19.

If "mark-room has been given" then rule 18 no longer applies and Yellow's actions are limited by Section B rules 14, 15, 16, 17. If "mark-room has NOT been given" then rule 18 still applies and Yellow's is exonerated if she breaks a rule of Section A of Part 2, rule 15, 16, or 31.

How Case 63 is written in the the 2021-2024 Case Book might help.

Hi Mark,

I agree with you. The new definition of mark-room includes "or pass":

(b)    room to round or pass the mark as necessary to sail the course without touching the mark..

I suppose one could always have argued that under the current rules, "to round" implied that mark-room continued to apply until a boat had rounded & passed the mark on to the next  leg of the course - merely passing the mark was not enough. And this is the interpretation that has prevailed.

Given the new definition that includes "or pass" the mark, however, obviously revives the old argument. Nevertheless, I'm happy with how the current interpretation works and I hope it is maintained under the new rules. That is to say; at position 2 in the diagram above, Yellow's proper course under 18.2(c)(2) is almost certainly to luff up to a close-hauled course - and she will enjoy mark-room & exoneration rights under 43.1 until she has passed the mark. 

Philip H. re: "The boat with mark room can go as wide as she wishes and turn up."

I'd be careful with that generalization. 

A ROW boat with mark-room can make a wide "tactical rounding", but a Keep-clear boat with mark-room might not be able to unless the ROW boat freely provides her that room.

Case  70 vs Case  75 

Ang

Angelo, "the boat" in my comments refers to the mark room boat in this instance. She was clear ahead till after she turned up. At that point she was leeward boat. At all times she had mark room and ROW. Hence, she can go as wide as she pleases. The other boat enters at her peril.

OK Philip .. it's just that you prefaced that comment referring to the "The 2 Daves .. " .. then your rule of thumb followed directly after.  A reader could have very easily interpreted that statement as a general rule-of-thumb being recounted by very trusted rule-sources.  

If you go back and reread what you posted, I think you will see what I'm getting at.

I just didn't want anyone reading the thread to learn the rules to walk away with an incorrect notion. 

Ang