IMHO
It is two separate incidents.
At position 1-2, no foul.  Blue was within it's rights to luff and fulfilled it's obligation top provide Yellow enough room for Yellow to keep clear.  Yellow kept clear.  There was no contact.
At position 4-5  There is not enough information to determine foul/no foul.
What caused the gap to close?  The luff of Blue or the lack of response by Yellow?
If the first, no foul.  If the second, penalty on Yellow.
Both 11 and 16.1 apply.  What conflict is perceived ?

Rob, I agree. 2 incidents. 

At the end of #2, Blue only has to provide Yellow room for her stern swing to allow her to keep clear. Blue heading as far off as she does at #3 is her choice ... (maybe attempting to regain speed one could conjecture .. but doesn’t matter why)

Yellow has every right to fall off into at least some of that excess room that Blue provides as long as she keeps clear, which she is based upon #3-#4 in the drawing. 

As drawn, Blue is continuously changing course between #3-#5 therefore at each incremental moment of course change, Blue owes Yellow a new opportunity to keep clear.  Since she is overlapped bow to stern that includes room for Yellow’s stern swing. 

To me, the key is #4 as drawn. If both boats hold those courses, they stay apart and Yellow keeps clear.  

It doesn’t much matter what happened before #4 IMO. 

PS: A couple US Appeals to chew on ...

US Appeal 108 is close to this scenario and may provide some insight. 

In regards to the question of “1 or 2 incidents”, US65 speaks to that. 

I agree with the above, but would like to put my understanding in slightly different terms.   Please let me know if my thought process makes sense.  The key for me is that Yellow, at no time has any obligation to ANTICIPATE Blue's course changes, AND giver her room to execute whatever course change she desires.  She need only respond to what course change Blue actually makes at any particular moment, and then she must do her best to keep clear.  if Blue, by her actions, limits Yellow's ability to keep clear, e.g. not allowing room for her stern swing, then Blue cannot luff further, and Yellow has kept clear.  So, between positions 4 and 5, yellow is under no obligation to change course until Blue heads up further.  From the diagram, it appears that both boats are continually making course changes (Yellow in response to Blue), until Yellow could do no more to keep clear.   

Blue intends to luff head to wind from position 3.  Intent may not matter a lot.

Starting at position 3 (or 3.5), it seems that Yellow could respond with a tighter turn, but does not, and so throws away her room to keep clear.

At position 5, Blue is prevented from turning more toward the wind due to Yellow's proximity.

So, is this now an accepted tactic for the windward boat (Yellow)?  Just sail out of the initially available maneuvering room and that curtails Leeward's ability to luff?

Even if you consider the "don't need to anticipate" rule, the fact that Blue is already turning at position 3.5, she has established a yaw rotational velocity.  So no anticipation should be needed... Blue is turning.  Yellow should not need to anticipate anything to realize the boats will converge unless she matches or exceeds Blue's yaw rate, no?

Does "course change" in rule 16.1 disregard any established, initial angular rotation?  And if so, is that a good rule?

Matt, I think I see where you are getting off the path with this statement.

There is no rule which establishes the right of a boat to maintain a rate-of-turn, once established. Rather, 16 is concerned when a ROW boat changes course.   

When thinking about 16 it is best to think of a film-movie-roll, each frame of film capturing the instantaneous position and direction of movement of the boats.  At each frame you ask, ‘what if both boats move forward using only this frame?’

This is why I focused on #4.  That’s my film-frame ... and if Blue does not change course from #4, Yellow does not need to even alter course to keep clear.

When a ROW boat is making a smooth turn, they are making an infinite number of Infinitely small course changes in infinitely small units of time (sorry, for the calculus lesson). At each moment, the ROW boat can stop turning and at each following moment, if they continue to turn, their obligation to provide the keep-clear boat an opportunity to so, resets. 

Erase #1-#3 leaving only #4-#5.   That is the crux of your scenario.  

Angelo,
I don't disagree with you on how the rules are interpreted these days.

But is that a good rule?  It certainly curtails Blue's ability to luff, which was a reasonably long standing tactic in the past.

"Course" might have many different definitions, depending on the context.

"At each moment, the ROW boat can stop turning and ..."  could be considered to be a "change of course."

I would like to see the rule accept that each boat's "course" considers the totality of its motions at any point in time, including both linear and angular velocities.  Not a movie film, but a GPS or iPhone record.  I personally think the "infinite number of Infinitely small course changes in infinitely small units of time" that ignores a boat's rotational (yaw) velocity at each point in time is an artificially filtered way of looking at reality.

And, I maintain that this scenario shows how rule 16.1 is in conflict with rule 11.  Blue luffed relatively casually in each case, and in both cases Yellow's even more casual response, causing her to sail out of her room to keep clear, put her in the privileged position to curtail Blue's luff.   I personally don't think that is a desirable consequence of rule 16.1.

My perspective as a competitor; I welcome all of your thoughts on this approach:

If I'm Windward (Yellow), I have no idea how much or quickly leeward (blue) is going to luff up. Rule 11 requires me to keep clear no matter how fast they luff up, and how much. It doesn't matter if they luff one degree or 90. Therefore, I need to respond to the most extreme scenario -- a fast luff to head-to-wind -- and push my tiller over hard to go head-to-wind. If my stern swings and hits blue/leeward, they're in violation of rules 15 and 16.1: they didn't give me room to keep clear.

If I'm Leeward (Blue), I need to comply with rules 15 and 16.1. I need to give Yellow/Windward room to turn up. This implies that 1) I establish an overlap with at least quarter boatlength gap between the end of their boom and my windward side; and 2) I do not luff until my pivot point (center of later resistance) is ahead of Windward/Yellow's. This gives them plenty of room to luff higher and turn faster than me, without hitting me, and thus keep clear.

Applying this thinking to the above scenario, Leeward/Blue breaks rules 15 and 16.1 at positions 2 and 5. Blue initiates a luff from behind yellow's pivot point, and in both of those situations, if Yellow had fully met her rule 11 obligation to keep clear, her stern corner would have hit blue.

That's my thinking if I were on a protest committee hearing case. What do you think?

For the purposes of 16, course is the instantaneous direction the boat is moving through the water. 

Yes, in the common vernacular, 2 people might talk about a circular-course, a zig-zag course, a wavering-course, alternating-course, triangular course ... but that’s not what it means in Rule 16.  

Even within the RRS, “course” is contextual. I did a post a while back which explored this very topic. 

https://www.racingrulesofsailing.org/posts/262-of-course-as-we-course-through-the-possibilities-we-understand-course-in-due-course

Angelo,
I liked the "course" definition thread you pointed to.  But, I did not see that it got resolved.

No doubt, that is the usual interpretation/assumption.  But that interpretation/assumption does not appear in the rules, does it?

In something like a port/starboard, that interpretation is probably good enough.  But in a luffing maneuver, where a large part of the motion of the boats is rotational, it falls short of what is desired.  It ignores 83% of the velocity vector components, not to mention other higher order inertial components.  In my view, the point of rule 16.1 **should be** to enable the give way boat to be able to predict where the ROW boat is going to be at the closest point of approach so the give-way boat can avoid the ROW boat (in the future, at the point in time when the risk of collision would turn into an actual collision if nothing changed), and assuming the ROW boat "does not change its present (average) motion."  In a luffing maneuver, the give-way boat cannot possibly figure out where the ROW **actually will be** by assuming the ROW boat instantaneously stops its rate of turn in mid-stride (which is impossible).  "Maintaining course" in the context of a luffing maneuver should mean "maintaining and not changing the boat's (average) motion, including all degrees of freedom and including rate of turn."  How that gets codified, I am not sure, but I suspect it can be done.

Food for thought.

Matthew,
US Appeal 33 states
Question
What is the meaning of “change course” in rules 16.1 and 16.2? Is it a change of course for a boat to sail an arc of a circle? If she does not move her helm in doing so, is she nonetheless changing course?
Answer
Yes, a boat changes course when she sails the arc of a circle or any other course where she changes direction, whether or not she moves her helm. This includes a change from moving forward to moving backward, or vice-versa. To change course means to change the direction in which the boat is heading or moving.
November 1974

So I think it's settled.
You might like this Dick Rose Article - a bit old but I think the point he makes is still valid.  If you luff from a trailing leeward position the physics will result in a collision if the leeward boat does not curtail the luff.  This means that in a protest the leeward trailing boat will have a hard time proving they gave room to keep clear - that's my interpretation.  Better to get bow out before luffing.
https://www.sailingworld.com/young-sailors-are-not-alone-in-breaking-these-essential-racing-rules/

Out of Angelo's infinite course changes, I think I would start by asking what was Blues last course change and did they give room to keep clear at that point, as that is likely to be the most damning of blue's course changes.. But not the whole story.

Since there was no collision in our facts, I presume it would be found that Blue did give room even if technically they didn't. (see US Appeal 119 where, in the first incident, the leeward boat overtakes within inches causing a technical foul by the windward boat but is still held to have given room as there was no collision.)
 
And Al,
If the windward boat luffs hard, causing her stern to hit the luffing boat, I agree that usually the leeward boat will lose the protest but Case 24 says "However, if A [the windward boat being overtaken to leeward] luffed higher than was necessary to keep clear of B [the leeward boat] and as a result caused contact with B, A has been given the room required and is not exonerated. "

Bob, thanks for pointing out Case 24.

In case 24, I'd interpret "luffed higher than was necessary to keep clear" to mean Windward luffing past head-to-wind.

Here's why:

If I'm Windward, I need to prepare for the possibility that Leeward might luff all the way to head-to-wind. However, I shouldn't assume that Leeward will go past head-to-wind in her luff, since that would put them at risk of breaking Rule 13 ("If two boats are subject to this rule at the same time, the one on the other’s port side or the one astern shall keep clear.")

I could see someone interpreting Case 24 as implying that Windward should somehow know in advance how many degrees Leeward is going to luff and turn just enough so that their stern doesn't hit. But there's no way for Windward to know this in advance. Because competitors should not be expected to have psychic abilities, Windward needs to always turn head to wind, and Leeward always needs to assume that Windward's stern will swing out accordingly.

For the record, I’m no longer IU,  I’m now IJ NU - I’m not umpiring much any more.

Anyway, for me, just going on the diagram, Yellow did not respond promptly nor adequately between 4 f 5 and so did not keep clear - penalty Yellow.

The rules create, as intended, rights and responsibilities by which boats can manoeuvre without making contact. In the subject type of scenario, Windward just has to do everything she can to keep clear - Respond promptly & adequately - she can’t sit there and wonder whether she has to respond. Leeward on the other hand, has to ensure she gives Windward sufficient room to act promptly and adequately.

I think it’s unhelpful to over-analyse scenarios. “Promptly” for me, is clear. It means a reaction response is required, an immediate reaction to the danger of not keeping clear, of not complying with the responsibility of a give-way boat to keep clear. Adequately for me means continuing to do everything I can to keep clear.

Re: infinite number of infinitesimal course changes ...

Think about twirling a ball on a string overhead.  It carves a perfect arc through the air.  The moment u let go of the string, the ball flys off at its last momentary “course”. 

In regard to the OP, I’m not making a judgement about whether it is Blue or Yellow that breaks a rule, only that at #4, if both Blue and Yellow hold their course, Yellow is keeping clear. 

Hi Ange,
       @ 4, if both Blue and Yellow hold their course, Yellow is keeping clear.
Sure, your quite correct, but Leeward Blue has the right to manoeuvre wherever she wishes, as long as she gives the Windward Yellow room to keep clear. When she luffs, Yellow has to respond promptly and adequately as I’ve explained. She can’t tarry, she must act straight away, even if she has to tack to keep clear.
In a jury room, faced with a diagram such as the subject one, Windward Yellow is going to have a hard time satisfying a jury that she complied with her responsibilities.

Phil, no disagreement from me with that.  Yellow is likely in a bind. My only point is that she was keeping clear at #4 and so it comes down to what happened between 4-5. 

It’s harder to luff a boat up hard when you are aft of abeam of her. Much better to be even or better yet slightly ahead, as the geometry works much better and leaves less excuses for windward. 

Yes, Leeward must take care to allow for the ability of Windward to respond. On the other hand, Windward can find herself in hot water if she attempts to use 16.1 as a sword rather than a shield. The best defence against a luff is do your best to keep clear in the first place.

Phil, what type of luff to head-to-wind constitutes using 16.1 as a sword not a shield?

Hi Al,
In this case the sword is in the hand of Blue and the shield in Yellow's hands. In the good old days a leeward ROW boat could luff as she pleased and as hard as she pleased. But the rule 11 ROW sword was blunted  and a shield given to Give-Way by rule 16.

Leeward can still wield the sword by luffing, but she has to give Windward room to avoid the blow with the shield. Maybe that change has caused more difficulties than the certainty it replaced. Nevertheless, them's are the rules - Leeward has to give room to keep clear when she luffs.

Unfortunately, Yellow's responsibilities are not as clearly understood as are Blue's. Blue must respond "promptly and adequately".- "promptly" nearly always means 'immediately' and "adequately" means 'neither too little nor too much'. Those are the defining factors judges and umpires will ask themselves; was room given and did give-way respond promptly and adequately. And as ROW  manoeuvres, so too must Give-Way. Yellow can't wait for the gauge to close and then claim she wasn't given room.

A umpires dialog might be something like;
Blue umpire "giving you room"
Yellow umpire "Agreed - keeping clear", or

Blue ump "giving you room "
Yellow ump " Negative - responded promptly  - can't keep clear.

And so it goes. The same thing happens in the protest room when finding the facts..

I've included the little diagram above to illustrate how Yellow could have kept clear by responding promptly & adequately.

Phil... that is a great overview of the situation, and addresses some of a question that has been brewing...

Angelo says that at position 4 in the original diagram, Yellow is "keeping clear" or words to that effect.  But is that really true?  Between position 3 and position 4, yellow as become closer to blue.  Would not becoming closer to the ROW increase the "risk of collision" ?  So, maybe the fact that the relative separation decreases during the maneuver is evidence that Yellow is not keeping clear? 

So, at what point is it appropriate for Blue to "protest?"

Blue's luff starts somewhere at position 3, or very shortly after she hails "come up" to yellow  Yellow is early and close to the line, so she does not respond as sharply as she could, but she does respond as much as she thinks she needs to.  Blue contends that if Yellow had turned sharper and/or sooner, then she would not have been so close to blue at position 5.

Also, Blue contends that she could not herself luff sharper starting at position 3, and definitely at 4, for fear of failing to provide Yellow with room to keep clear.

So, would it have been better for Blue to hail protest earlier in the maneuver, say at position 3.5?  What position is appropriate?

Phil, I’d like to add an observation to your post if I may. 

One crux of this biscuit is that Leeward’s (L) ability to luff Windward (W) up quickly is limited when she is aft of abeam of W.   The further aft of abeam she is, the more limited she will be as the geometry of L’s bow and W’s stern swing toward each other.  

This situation is completely different when L is at least abeam or better for L, forward.  Then W is only limited by how fast her boat can rotate and L can safely be more aggressive. 

In other words in the OP, IMO Blue is not fully tactically in the position to pull off what she’s trying to do. It’s possible, but it’s a gambit, especially that far from the line. We can imagine positions #6-7 that look very much like #2-3 leaving Yellow running the line at full speed and Blue blanketed, slow in the second row. 

Angelo, that is pretty much what happened.  

So, what (if anything) could blue have done in this situation to "force" yellow up earlier/longer, and not permit her to so quickly claw back the meager, but hard earned gains at pos. 2, and to enable blue to get out from under yellow for some clear air at the start?  

Blue had decided to take yellow's stern at position 1 because blue did not like the "barging" position to weather of yellow, and the pin end was favored, and both boats were early (the diagram may not correctly show all that).  There were other boats further down the starting line that made reaching off further after passing yellow not a good option for blue.

Frankly, both boats had bad starts... yellow because she needed to take a penalty, and blue because she was in yellow's wind shadow.  They each ended up scoring 4 points for the race!

If yellow had delayed her bear-away at 2.5 until blue had some breathing room, then both boats could have had better starts, I think.

Matt, you’ll get better ideas from the match-racers on the forum, but I have a couple responses. 

First, Yellow isn’t “barging” at #1. Follow the lay line from #1 and Y is 2BL’s below the RC layline.  To be “barging” (based on its common use), Yellow would need to be above the layline that intersects the RC and Blue would be close hauled on the RC layline with insufficient room for Yellow to pass beteeen Blue and the RC. 

IMO Blue is trying to do a hard thing here. B gets to fall-off between 2-3 first which would have given her the opportunity to accelerate first. If Blue fell off between 2-3 to a “footing” close hailed course instead of a reach, she might have moved into the space Yellow needed to fall off to accelerate, and crossed the line bow-out in front of Yellow with Yellow sliding back into her backwind. 

At position "0" yellow was on RC boat layline, and blue was above her.  But there was 50 seconds, or so, to go.  The two boats stalled in that location for awhile.  And, the diagram is probably not 100% correct with respect to the RC boat location.  Also the start line is probably 2 or 3 times longer than shown.  The pin end was favored, as was the left side of the course (so why are we at the RC boat?).  So, blue though taking yellow's stern was a better alternative than staying put.

Yellow was very quick to fall off at position 2.5, which enabled her to smother blue at position 3 and prevent her from gaining speed - yellow had clear air and was able to accelerate faster.  Blue could/did not accelerate as fast as yellow, and was going slower than yellow, so it was tough for blue to develop a bow out position.

I am now leaning towards the notion that blue could have just held the luff at 2 until the very end.  Yellow might have broken off and tacked around, or ben forced over the line early, or maybe blue might have drifted bow-even with yellow to enable clear air.

In the old days, blue would have executed much faster luffs.  

"Course" needs to be replaced with "Motion", and US appeal 33 changed (a steady arc is a course!).  My view.

That rarely pays-off in a fleet race unless Blue is the only boat you need to beat for your standing in a regatta because many of your competitors are hitting the line at full speed. 

Dingy sailing ... sure. 

Hey Matt,

Yeah, Yellow is keeping clear at 4.
When boats are overlapped, the give-way boat is keeping clear "if the ROW boat can change course in either direction without immediately making contact". At 4, even though the gauge has closed, it is clear that Blue can change course in either direction without immediately making contact. It really matters not that the boats have become closer between 3 & 4 except, as you say, Yellow has increased the danger to herself. As inside the turning circle between 4 & 5, Yellow will have a tighter turn than outside Blue so her reactions must be bolder than those of Blue..
Certainly, if Blue has to curtail her luff (never make avoidable contact with a give-way boat) hail protest and lodge the protest when ashore. One doesn't have to lodge a protest, but the hail will at the very least unsettle the other crew. It's wise, however, not to develop a reputation for hailing but not lodging the protest form.
It often occurs in match & team racing that Windward will attempt to drive across the bow of Leeward so as to escape to leeward of her opponent. Such might have been Yellow's motive between 2 & 3 in the subject scenario. When Blue fears Yellow with more speed might achieve her aim, Blue's defence would be to bear away, rather than continue her luff. If Blue had the greater speed at 2 as the diagram indicates, why did Blue bear away and let Yellow off the hook? 
As Angelo has pointed out, an option for Blue at position 2 was to hold her luff. From the diagram Blue was moving faster, but we only have the diagram and the merits of the case would depend on all the details - what the umpires saw or what facts the judges determined from the evidence.
Matt, I don't know if you've done this before, but get hold of some small different coloured model boats with booms on them, and set them up on a table top. Move them around using them to illustrate different manoeuvres so that a better understanding of tactics and the rules can be attained. Back in the 1990's I recall sitting together with a friend in the back of an aircraft on our way to a umpire seminar. We both had our models out and were moving them around the seat-back tables when I looked up to see the hostess looking at us in a very strange way.

Phil,
Maybe you hit on the crux of my question...

So, if Blue curtails her luff because she needs to give yellow room to keep clear, does blue win that protest?  Is the "room to keep clear" rule there primarily to prevent contact, but because yellow sailed so close to blue, she is still culpable on rule 11?  Or does  rule 16.1 "room to keep clear" give yellow "an out" from responding to a continuing luff and rule 11?

Most of what I read here tells me that 16.1 trumps 11 and curtails the luff, and Yellow becomes privileged at the point that yellow needs room for her stern to swing, or whatever.  Blue is no longer ROW as long as yellow needs room to stay clear.  

But, the fact that you would penalize yellow and your last note gave me a ray of hope that it might be otherwise.

Phil, thank you for your diagram above. What I'm taking away from that is that Yellow needs to luff promptly to head-to-wind, but no further. Blue needs to anticipate Yellow's stern swinging out.

If Yellow were to luff past head-to-wind, that would mean an excessive turn of her stern towards Blue and constitute using 16.1 as a sword, not a shield.

Hi Guys,

Matt, please don't think that rule 16 bestows a privilege on the windward boat. From the moment Yellow becomes overlapped she has nothing but responsibilities under rules 11 & 14 and must keep clear.

And Al, at the moment Yellow passes head to wind, the boats are on opposite tacks and Yellow is subject to rule 13 & 14. And there are limitations on both boats.

Everyone should study the Calls B1 & B2 in the Team Racing call book, and B3, B4, B5 & B6 in the Match Racing call book. Yes, I know that calls are not "authoritative" in fleet racing, but they nevertheless explain the working of the rules in practice.

I think the USSA Appeal 108 throws in an interesting prospective.

Summary: When a leeward boat is changing course toward a windward boat, she may need to change course away from the windward boat when the boats get near each other in order to continue to give the windward boat room to keep clear.

Kim

Phil,
That clears up a lot in my mind.

This has been something I have been having a hard time understanding and accepting.  I kept gravitating towards the notion that only one boat is ROW and the other one is give way at any point in time and that "some rules trumped other rules" and one needed to figure out the net sum of the rules in play to determine the ROW boat (hence, my earlier discussion where 16.1 trumped 11), and, under this notion, the ROW gets to be king in choosing her course.   Even though we may be looking at a single maneuvering event, I now see that one needs to consider individually each and every rule in play at every point in time, and boats can each be ROW and give-way simultaneously.

No, no, no Matthew. I have obviously led you astray. I’m sorry. Look, leeward Blue is ROW & windward Yellow is give-way. The limitation of Blue having to give Yellow room to keep clear imposed by 16.1 does not  not make Yellow ROW.

Rule16.1 gives Yellow room to get out but she’s still give-way and if she doesn’t take the room given - and take it promptly - she risks breaking rule 11. Yellow is vulnerable throughout the luffing manoeuvre.

Have a look at the Calls I recommended. They are available free to download on the World Sailing website.

Until tonight, I never really paid attention to the Part 2 section titles: A-Right of Way, B- General Limitations, etc.

So I now see that R.O.W. is a designation applied (only) in the context of rules 10-13, not to all of Part 2.  That clears up some things, such as how you can be the R.O.W. boat, but be wrong!

Rules apply between pairs of boats and only one of the rules of Section A, Right of Way rules of Part 2 applies at a time. Also note that one boat has right of way over the other boat when the other boat is required to keep clear of her. The right-of-way rules are written to define who has to keep clear, not who is the right-of-way boat. Some rules in Sections B, C and D limit the actions of a right-of-way boat. However, the limitations in Sections B, C and D do not change a keep clear boat's obligation to do everything she can to keep clear, which means respond promptly & adequately. The right-of-way boat in turn has to give the keep clear sufficient room to act promptly and adequately.

In the scenario presented.
 
Position 1 - When Blue becomes overlapped to leeward from clear astern and becomes the right-of-way boat under rule 11, Yellow must act promptly to keep clear.
 
Position 2 - Blue luffs immediately after she became overlapped to leeward of Yellow. Yellow was able to keep clear, so Blue's luff does not break 15 or 16.1. Yellow keeps clear so does not break rule 11.

Position 3 - Blue and Yellow bear away. However, Yellow appears to have born away further than Blue, which will make it more difficult for her to keep clear if there is another luff. 
 
Position 4 - Blue luffs again, rule 15 does not apply, only rule 16.1. Yellow must again act promptly to keep clear. However, by bearing away to a lower course at position 3 she has made it more difficult for her to keep clear. It appears from the diagram that Yellow does not respond immediately or adequately as the gage continues to close.

Position 5 - Blue continues to luff and has to curtail her luff to avoid contact with Yellow. At this point Yellow breaks rule 11. We have to Judge; 1) did Yellow respond immediately and adequately to Blue's luff, or 2) there was no seamanlike action that would enable Yellow to keep clear. If the former then Yellow would be disqualified for breaking rule 11. If the later (2) then Blue's luff breaks rule 16.1, and Yellow would be exonerated for breaking rule 11, under rule 64.1(a).

My inclination is that Yellow failed to respond immediately and adequately enough to Blue's luff. But additional facts might persuade me otherwise. 

Another more general observation is that US Judges and Umpires tend to give more weight to rule 16.1 than some of our fellow Judges in other parts of the World. As one of my Australian friends said as we penalized the keep clear boat, "... he put himself there."

Mark...
I am struggling to understand the implications of your discussion of position 5.

1st, if yellow had luffed hard at position 3.5, just after blue's luff started, then she (probably) would not have been that close to blue at position 5.  Doesn't that have a bearing on this, and no matter what yellow does after position 3.5, she did not maneuver promptly or sufficiently at 3.5?

2nd, Blue stopped turning to windward at some point just prior to position 5 to avoid contact with yellow and to permit yellow to have sufficient room to head up more.  Blue wanted to turn further towards the wind, but Blue judged that she needed to stop turning to satisfy rules 16.1 and 14.  Isn't that enough to say that Yellow hindered Blue?  Or can Yellow just say she ran out of maneuvering room, and that fully exonerates her? 

3rd. If yellow is exonerated at position 5, what are the steps that could follow, assuming Blue wants to continue to luff Yellow?  Assuming Yellow turns a little more so as head closer to the wind than Blue, can Blue follow and turn a little more toward the wind (all the while keeping clear of yellow's stern) and we keep repeating these baby-steps until blue is fully head to wind?  Even though Blue's luff is "curtailed" by being interrupted, or slowed, yellow is clear (exonerated) all the way through this maneuver?

Are the responses by Phil M and Mark T. in agreement, or are differing assessments presented by each? I am having a hard time understanding the nuances in this situation.  Is Yellow penalized or exonerated?  As long as Yellow responds by heading up, is she ever penalized? Is Blue in any jeopardy if there is no contact?  Is Blue's case strengthened by getting close to Yellow, or stopping luff when 3 to 5 feet away from Yellow?

I don't understand some of the interpretations.  Since it seems to me that the rules are pretty simple on this one, I would like some commentary as to what is incorrect about my thoughts on this.  Listing rules in the order of the events:

First, rule 12.  Blue comes from astern of yellow - yellow has right of way according to 12.

When boats are on the same tack and not overlapped, a boat clear astern shall keep clear of a boat clear ahead.

Next, rule 15.  Blue overlaps yellow to leeward of yellow - Blue must allow space for yellow to keep clear "initially".  Initially would seem to mean just enough time to make the transition until the next rule

When a boat acquires right of way, she shall initially give the other boat room to keep clear, unless she acquires right of way because of the other boat's actions.

Now "initially is over at point 3 at least, so transition to rule 11.  This rule says yellow shall keep clear.  There is no limitation on the leeward boat (blue) as long as it is on the same tack.

When boats are on the same tack and overlapped, a windward boat shall keep clear of a leeward boat.

Now transition to maneuvering and rule 14.  Rule 14 states that a right of way boat need not act to avoid contact until it is clear that the other boat is not keeping clear.

A boat shall avoid contact with another boat if reasonably possible.  However, a right-of-way boat or one entitled to room or mark-room 

So, it seems to me that, except for the initial transition of right of way, the right of way boat may maneuver in any way that does not change those rights.  The give way boat has fouled the right of way boat if the right of way boat has to avoid the give way boat.  I see no limitation on the right of way boat other than to avoid contact.  

My interpretation is that the main issue then becomes the term initially for the transition of right of way from yellow to blue, which starts at 1 in the diagram.  If yellow were moving very slowly, then blue would have to be sure yellow would be able to avoid blue once blue obtained rights.  That might take some time, but it would not require that  blue allow yellow to bear off to gain speed for example, only that yellow be able to keep clear of blue.  I see only this transition, and once done, yellow must keep clear of blue.  If yellow choses to stay close to blue for tactical reasons, she does so at risk because blue is allowed to maneuver any way she likes.  Blue cannot protest if yellow keeps clear, which she might do even in close quarters, but blue does not have to provide yellow room to keep clear once the initial transition of rights has occurred.

For the situation diagrammed, yellow bore off too far in the transition from position 2 to position 3 and did not provide enough room to keep clear of blue.  Yellow could have stayed on a higher course and been safe, so the initial transition of rights was adequately made by blue.  Eventually yellow fouled blue. 

Please correct what I have wrong here as this is a very common situation.  Thanks.

You omitted rule 16 from your list.

16 CHANGING COURSE
16.1 When a right-of-way boat changes course, she shall give the other boat room to keep clear.

Rule 11 says that when two boats on the same tack are overlapped the windward boat shall keep clear.  A leeward boat's actions, however, are limited by rule 16.1. If there was room for windward (Yellow) to keep clear when leeward (Blue) luffed, leeward (Blue) did not break rule 16.1.

Thanks for noting rule 16.1 Mark.  I did miss that.  
Rule 16.1 really muddies the water.  16.1 is in direct conflict with rule 14.  Rule 16.1 allows a make-way boat to maneuver to restrict a right-of-way boat by staying close enough to invoke rule 16.1 and thus put the burden on the right-of-way boat.   Rule 16.1 could be applied in this case and I think this is a major flaw.  Note that I was present on the yellow boat.  This may not have been the intent of the helmsman, but the maneuvers of the yellow boat did restrict the maneuvers of the blue boat.  The yellow boat did put itself in a position from which it could not keep clear and rule 16.1 could apply, but yellow could have prevented this situation had it taken the traditional approach of keeping a good space to the leeward boat.  If rule 16.1 allows the windward boat to maneuver in these ways, then the prestart/start is going to be much different.  A weather boat can just squeeze a leeward boat, especially taking advantage of the "initially" part of rule 15 to extend initially to continuously by means of rule 16.1, or, as was the case here, reestablish limitations on the leeward boat.  In my experience it is much better to race under clear rules that remove the ambiguity produced by 16.1 and just stick with rule 14 for avoiding contact.  Clear cut responsibilities result in fairer, better and safer racing.  

Richard, Rule 16.1 is a Part 2, Section B General Limitations rule. Section B rules limit the actions of the right-of-way boat. The rules in Section B are as 14 AVOIDING CONTACT, 15 ACQUIRING RIGHT OF WAY, 16 CHANGING COURSE and 17 ON THE SAME TACK; PROPER COURSE.

I would also read the definition of keep clear, as well as World Sailing Cases 7, 13, 24 and 46.

The right-of-way boat (Blue) must allow the keep clear boat (Yellow) room to keep clear, and the keep clear boat (Yellow) must act promptly and sufficiently to keep clear. The keep clear boat (Yellow) does not have to anticipate that the right-of-way boat (Blue) will change course and isn't required to make unseamanlike maneuvers to keep clear. The right-of-way boat (Blue) is allowed to luff to head to wind before the start and the keep clear boat (Yellow) must respond and keep clear.

As there is no contact the leeward boat (Blue) gave the windward boat (Yellow) room to keep clear as required by rule 16.1.

However, the right-of-way boat (Blue) curtailed her luff, and the windward boat's sails are still full and drawing at position 5. This leads me to the conclusion that Yellow failed to act promptly and sufficiently to keep clear as required by rule 11 and should be disqualified.

Now that we have gone thru all the rules that apply, I would be asking the following:

In pos.1, 2, 3, and 4 is Y keeping clear? My answer: yes.
So, what happened between pos. 4 and 5 that brought the boats so close to each other?
Was the luff from pos. 4 to 5 by Blue too fast/high?  No. 

Looking at pos. 3 to 4, the change of course from Blue was significantly bigger than from pos. 4 to 5. Agree? Yet, Yellow was able to keep clear at pos. 4.

So, we know that Blue did not luff hard yet Yellow is much closer to Blue at pos. 5.

That suggests that Yellow’s reaction to Blue’s luff was not sufficient to keep the gauge between the two boats at minimum, the same as it was at pos. 4.

In Phil’s speak: At pos. 4, Yellow says: Keeping clear. Blue says: Agree. Blue say: Up, Up.  Yellow says: Could be doing more; Blue says: Protest. Yellow says: did not do enough, early enough.
Penalty: Yellow.

Question: In pos. 5, could the ROW boat (Blue) change course in both directions without immediately making contact? [Def. Keep Clear (b)].
My answer: Lucy, I don’t think sooo.

DSQ Yellow. Rule 11.

Kim

I'm a little hesitant about calculating rates of turn and so on from diagrams.  A diagram is only as good as what the author meant to show.

I think the key question is what happens next.

@5 I don't think there is any doubt that B cannot change course to windward without immediately making contact with Y, and I think this applied from some little time before @5, say @5 minus delta.  At that point Y was breaking rule 11, and had had the opportunity to change course further to windward to keep clear.

@5 plus delta, if Y changes course any further to windward, her stern must contact B, and I would say, that, contact being made, B  has not give Y room to keep clear, B breaks rule 16.1 and Y is exonerated for breaking rule 11 by rule 21.

On the other hand, if @5 plus delta B bears away, she is then giving Y room to keep clear, but Y has already broken rule 11 and on valid protest should be penalised.

John, If I understand your @5 plus delta correctly it appears that you are saying that if Y's stern swings into B, Y will be exonerated.  Y was in a position  to do this.  Are you saying that doing so would exonerate Y and penalize B?

Yes.

I think I'm echoing Mark T