I like the way the RRS for the America's Cup handled this. They changed the last sentence to "Rule 18 no longer applies between yachts when the yacht entitled to mark-room is on the next leg and the mark is astern of her."

Mark-Room - Room for a boat to leave a mark on the required side. Also,
(a) room to sail to the mark when her proper course is to sail close to it, and
(b) room to round or pass the mark as necessary to sail the course without
touching the mark.

The incident described in case 144 requires a determination of whether or not boat A has been given mark-room.   If it is determined that A's proper course is to sail towards the next mark on a reach (ie, in the absence of strong tidal flow or other influences),  then, in respect of (a) and (b), A has been given mark-room.  At position 4, her proper course is no longer to sail close to the mark and therefore A is not entitled to room to sail to the mark. Also,  A has room to sail the course without touching the mark.

The question is then, has A been given room to leave the mark on the required side?   My answer would be yes.  A has room to be able to continue to sail her course at position 4 and leave the mark on the required side.  If A chooses to not use the room she has been given and instead luffs to position 5, that does not change the fact that mark-room has already been given, and therefore rule 18 no longer applies.

Here is another my argument  about the unnecessary / harmfulness of the last sentence of rule 18.1 - the need to explain why the correct answer to the question in the picture is still “YES” (see also Q&A 2009-036   https://www.sailing.org/tools/documents/QA2009036-[7516].pdf?fbclid=IwAR0nEn9r8uBkx8JJnFJs12Z-93Q5eWTrsaAxj-GRX0qDhW58Dcw264AvFSo )

Boris Kuzminov 

I would argue that the correct answer is actually "NO".
Firstly, let us consider if both boats had been sailing on starboard tack and overlapped when they entered the zone.  At position 2, Blue would be entitled to mark-room to leave the mark on her port side.  At position 3, mark-room has been given and therefore the last sentence of R18.1 turns off R18.  It is clearly the intent of the last sentence of R18.1 that R18 should be turned off when the mark is no longer influencing the course of the boats.

In the diagram, at position 1, R18 does not apply.  When Blue tacks into position 2, she breaks no rule.  At this point, R18.3 applies and R18.2 does not.  Neither boat is entitled to mark-room (Yellow can only be entitled to mark-room if she establishes an inside overlap at position 2).  Can mark-room be given to a boat that is not entitled to it?  If the answer to that question is no, then R18 cannot be turned off by the last sentence of R18.1.   In this case, it is the first sentence of R18 that turns R18 off.  

In position 3, both boats having already left the mark on the same side, are no longer required to do so in order to sail the course.  The mark is no longer influencing the course the boats take in order to sail the course.  R18 no longer applies.

What a mess!

There are 2 issues here.  Connected, but separate.

Issue A - Prevent the switch of mark-room from one boat to the other during a single instance of a rounding caused by the lingering instance of 18.2(a).  Solved by turning off rule 18 after mark-room is given. (e.g. move the 'OFF'-switch from 18.2(d) to last sentece of 18.1. per 2021 change.)

Issue B - Interpret the word 'pass' found in the definition of mark-room, in order to determine when mark-room has been given.  Not yet interpreted.  World is very confused!

How do YOU interpret the word 'Pass' in the definition of mark-room?

Interpretation 1 = Pass - move until something is 'past'. (e.g. until it is 'clear behind' you.)
Interpretation 2 = Pass - move while something is on one side of you. (But not necessarily requiring it to be behind you.)

The beauty of the English language is that it so colourful, and the same word may be interpreted in many ways!  That's a problem for rule makers.  That's why we need interpretations

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The root of the problem

Match racing call E2 boldly embraced Interpretation 1, saying that mark-room was only given after the boat's transom had cleared the mark.  This is fine for match-racing, which requires bold demarcation for the umpires to make split decisions, and where the boats are generally doing the same thing, on a very closed course, with boats sailing more aggressive boat-on-boat tactics.

Unfortunately, for the last 4 years, half of the fleet racing world has latched onto that call (as the only official interpretation), but as we see from various diagrams and examples, it does not necessarily work in fleet racing.  Even Case 144 is problematic with an apparent use of the transom call (second sentence of answer 1), but wishy-washy proper course argument to invalidate the luff in A2, rather than both A1 and A2 uniformly asserting that mark-room had been given (the rules served their purpose) by virtue of the fact that Boat A did not need any more protection.

The mark-room rules presumably serve to organise the boats at the point on a race course of congestion and constriction so that they can proceed in an orderly and safe manner.

Interpretation 1 provides absurd protection to a boat even after the rules have served their purpose and given her room to proceed in an orderly and safe manner.

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Solving the problem - Interpretation 2 - 'Pass' as general non-geometric term

Another place where the word 'pass' is found is in the definition of 'Sailing the course'.  Here there is no mention of transoms.  It's just a term used when determining whether going left or right of something.  Definition of 'Sail the Course' uses Interpretation 2.

ROUND (= Sail in an arc close to something.) OR PASS (= Simply leaving something to the side (as opposed to sail into) using any track and possibly by some distance, without reference of the mark being behind the transom.)

Using this interpretation in the definition of mark-room, the requirement to know when a boat is 'past' the mark becomes less important (in fact irrelevant).  Mark-room is given when the rules have served their purpose, and a boat 'no longer needs' protection.

In other words it is perfectly plausible that

The rules committee hopefully will choose one or other interpretation of the word 'pass', and put this to sleep once and for all.

What for? Let us not be distracted pls.

The rules  that apply (it is a part of rule 18.3) in our situation  say nothing about "giving mark-room" (and even  about "mark-room" just) so your statement  "then R18 cannot be turned off by the last sentence of R18.1" is not correct IMO.

I do not agree. While the boats are on the leg begins by this mark, the requirement to leave the mark on the same side is retained (see rule 28). Also see Q&A 2009-036

I'd like to quote  Rob Overton (one of the rule-writers) from this thread  https://www.racingrulesofsailing.org/posts/274-contradiction-in-rule-18

It is clearly the intent that R18 be turned off once the mark no longer influences the course of the boat/s.

 Boris Kuzminov wrote

Once a boat has left the mark on the required side, it is the requirement for the string line representing the boat's wake to leave the mark on the required side that is retained.  If, after having left the mark on the required side, a current sets a boat to the other side of the mark, there is no requirement for the boat to leave the mark on any particular side as long as the definition of sail the course is met.  At position 5 in this diagram, Y can sail on starboard tack and leave the mark to starboard, or she could tack and leave it to port.  One of the conditions of the first sentence of R18 is met (inside the zone), but not both (not required to leave the mark on a particular side).

There says everywhere about  «mark-room/when mark-room has been given» - something that is not in our case. I repeat again - The rules  that apply (it is a part of rule 18.3) in our situation  say nothing about "giving mark-room" (and even  about "mark-room" just).

Do you think the authors of Q&A 2009-036 forgot about "first conditions" when they wrote - “If either boat is still in the zone, rule 18 continues to apply - see the first sentence of rule 18.1»? :)  In my opinion, they thought (same as me) that this is a matter of course - not even needing to be mentioned. 

Well and finally

 Obviously, the authors of the rules have a different point of view - otherwise why would they have come up with the last sentence in R18.1 (and earlier in R18.2(d))?

PS. And small illustration for words “when they are required to leave a

mark on the same side» :

Obviously it is to turn off R18 when mark-room has been given while the boats are still required to leave the mark on the same side.
Why would they remove the 12 year old  Q&A and not update it for the 2021-2024 RRS unless it was not considered of value (or maybe incorrect)?

Does Y break R18.3 in this diagram?  At positions 1 and 2 both boats are required to leave the mark to port. Y does so before the wind drops and current pushes both boats backwards. At position 2 R18.3 applies.   At position 4 the wind fills in. B is still required to leave the mark to port.  Y, having already left the mark to port, can sail from positions 4 to 5 leaving the mark to starboard and still comply with R28.1.  R18 applies when, both boats are required to leave the mark on the same side and  at least one is in the zone. 
At position 4, Y is no longer required to leave the mark to port. The time when she was required to do so was between positions 1 and 3 while the mark was influencing her course.  According to R18.1, R18 does not apply, as one, but not both of the conditions of the first sentence are met. 

I must admit I am uncomfortable with using the first sentence of rule 18.1 to turn off rule 18 in the way Murray suggests.

The mark is and remains a mark, as described in the SIs / definitions of Mark / Sail The Course, having a required side (which may be the same side for both boats) and this remains the case for the duration of the race.  The word 'required' as used in the first sentence of rule 18.1 refers to that regulatory requirement rather than the boat's immediate navigational requirement.

"Rule 18 applies between boats when they are required [by the rules] to leave a mark on the same side and at least one of them is in the zone."

The first sentence of rule 18.1 empowers rule 18 based on the regulatory requirement, regardless of boat orientation or geographical location of the boats, except that one must be in the zone.

*Murray, I accept that the word 'required' is open to interpretation, but think the regulatory interpretation [by the rules] is more logical here.

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This brings us back to the new last sentence and the question of when has mark-room been given, as the mechanism to turn off mark-room once boats are well past or have drifted around the mark.

Murray's diagrams quite clearly illustrate why the mark-room requirement cannot always be simply based on say, a line drawn from a boat's transom or solely based the geographical position or orientation of a boat. They show why in some cases mark-room requirement lingers or even 'lies-low' only to resurface again during the same instance of a mark rounding.  This alludes to my earlier post on this matter. This is where I think Match Racing Call E2 doesn't work for fleet racing. 

Instead, the quantum and longevity of mark-room requirement must logically be a function of the environmental conditions, where in some cases, it could be 'given' swiftly (with little or no intervention by the burdened boat) even before the entitled boat has passed the mark (See Case 144 diagram position 3), or in other cases (as per Murray's diagrams) mark-room may be needed well after a boat has passed the mark because that mark is in danger of being or becomes an issue again.

This is the concept which phrases such as 'no longer needs' or 'no longer influences her course' are trying to promote I guess.  That mark-room is not an exact science!  Absolute phrases such as 'has passed', 'is past', 'transom lines' are just not useful.

So until there is an interpretation of 'when mark-room ends', I will be following this:

Those environmental conditions must be assessed by the boat giving mark-room in determining how much room to give, and how long to give it for.  In the event of a dispute, it will be down to the protest committee/jury to assess those conditions, and determine whether mark-room was given or not.

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Rule 18.3 case is laughably complex.  At no point was Yellow required to give mark-room to Blue (nor Blue to Yellow), and Rule 18.3 does not have its own 'off-switch'.  So in position 6 Rule 18.3 technically still applies (neither first sentence nor last sentence have turned rule 18 off), so Yellow's luff is technically illegal.  This does not require Q&A2009-036 to come to that conclusion.

Is this what the rules intended?  Who knows? (Personally, I quite like it that way.)

Thank you very much Benjamin for your comment.

Murray, please read again Rob's comment about "The brief history of the words "or has been given that mark-room" in rule 18" (https://www.racingrulesofsailing.org/posts/274-contradiction-in-rule-18).