Blue was not an obstruction to Red or Green until position 3.
In all of the scenarios Red and Green were not obligated to begin altering course until position 3.
At that time, had Red and Green held their courses, Blue failed to give either boat room to avoid contact.
Perhaps the reason you do not find a case for your questions is that Blue had already violated 13 or 15, making the questions moot. 

Image 1, Are red and green at position 2 or is position 3 missing.  With a generous interpretation there is less than 2 boat lengths for Red to alter course ~3  seconds at speed Blue tacked too close, (15)  
In regard to your next question keeping clear, keeping clear entitles the other right of way boat to hold course. So your real question is "How long is "initially" per Rules 15. Depends on the boats and conditions. however 3 seconds is probably not long enough to allow Red to respond in a seaman line manner. 
Red has the right of way "initially" which is again to say long enough for a skilled sailor to recognize you completed the tack, and then time to alter course in a seaman like manner.  A crash tack or wild bear away would not be seamanlike. The question is did blue allow enough time for either, not necessarily both. 
Putting that aside.. If Green is an obstruction for both (having completed their tack and allowed time for the boats to respond)  The right of way boat (red, leeward) can pick which side but must allow room for green to round inside if they so choose (19.2 a and b). However if Blue was determined to have tacked too close, red could be exonerated, it would be wise for them to protest blue, since she broke the rule that forced their actions. 
Finally, if red determines the blue is an obstruction (19 a) and allows green several seconds to respond in a laser to respond to a hail to tack (20.1 20.2 a) green has broken Rule 20.2, if red must tack, they must also try to avoid collision, (14) but could be exonerated for breaking 13 or 15 since green did not respond to the hail.  If it was later found that red was not obstructed or could have avoided the impact with green conceivably red could be penalized. But green still broke rule 20.2  by not responding. 
If blue tacked so close that neither green nor red have serval seconds to respond, then red could be exonerated by blue breaking 15. 

Difficulty being "initially" and (enough) "time" are not defined and subject to interpretation.  A Laser with decent breeze may only need seconds to respond in a reasonable manner.  A larger boat, or rough conditions would change that.  Keeping clear ALWAY means holding course or ability to change course if overlapped, there is no time factor. Rule 15 ads the time...  IF it goes to a hearing, times, distances, witnesses are important.  Boat on starboard tack fetching will likely get a benefit of the doubt. 

It should be pointed out that Blue was always the right-of-way (ROW) boat in the initial diagram. By tacking from port to starboard, Blue did not “acquire” ROW.  If you want to include  RRS 13, While Tacking, in this discussion that would be more correct than RRS 15.

Thanks for the responses. And agreed, since Blue was always right of way, 15 wouldn't apply but 16 would.  I guess to restate my first question. Does room to keep clear after Blue changes course include the time for Red to hail for room to tack and for Green to respond? It sounds like the answer is "No." Red must duck and if they can't duck, then Blue has fouled. If Red can't provide Green room then Blue has caused Red to foul Green.

It seems like after ducking, Red could protest Blue if there isn't enough room for Green even if Green tacks as long as there wasn't room for Green to pass between Blue's transom and Red.

I do feel like this scenario is splitting hairs with the timing but it happens pretty frequently in dinghies sailing close together so figured a breakdown of how the rules apply would be helpful. It seems like if Red attempts to tack without Green responding then Red would likely lose the protest as the assumption would be that there would be room to duck.

When Blue completes her tack, she is initially required to give Red & Green the room to keep clear.  That room includes the space needed to respond promptly in a seamanlike way while not being forced to break any of the rules in Part 2.  If Blue does not give that room then she has broken rule 15.

Contrary to Philip's assertion, whether Red & Green could have held their courses and had room to keep clear is not relevant.  As the newly keep clear boats they must respond in some way unless holding course is their best way to keep clear.

As the ROW boat w.r.t. Green, Red is in control of the situation, i.e. she gets to decide whether to tack (using rule 20), try to cross ahead of Blue (which isn't an option here) or to duck Blue (with the limitations of rule 19).  These are her options to try and keep clear of Blue.  Red does have to pick a viable option.  Blue has to give both Red & Green a way out, but not all ways out.  If Red picks the wrong option, then she is not sailing in the room she is entitled to and does not get the benefit of exoneration.

Because Red & Green both have to keep clear of Blue, Blue is an obstruction to both and rule 19 applies between Red & Green.  As a result, Red has the option to pass on either side of Blue.  The option to stay on port and cross ahead of Blue isn't available to Red so rule 19 would only come into play if Red decides to duck Blue.  If she does try and duck, then she is required to give Green room to pass between them while Red & Green are overlapped.  If Green chooses to duck with Red and Red cannot give Green room then Blue may have broken 15 and Red could be exonerated for breaking 19 and Green for breaking 10.  This is the second scenario.

If Red ducks, Green is not obligated to follow and could tack away.  In this situation, Red & Green simply need the room to keep clear of Blue individually.  This is the first scenario.

If Red chooses to hail for room to tack and Green cannot respond appropriately and give Red that room then, again, Blue may have broken 15 and Green could be exonerated for breaking rules 10, 11, & 20 and Red could be exonerated for breaking 10, 13, & 20.  This is the third scenario.

Blue is not overlapped or being overtaken in 1. Regardless you cannot be right of way while tacking (13) and a new relationship is established since completing her tack gave her the right of way in this scenario 

Blue becomes a keep clear boat from the time she passes head to wind until she reaches a close-hauled course on starboard.(RRS13)
When she reaches close hauled on starboard she acquires right of way (RRS10 and must initially give room to both Red and Green to keep clear (RRS15)

The definition of room is clear:
Room The space a boat needs in the existing conditions, including space to comply with her obligations under the rules of Part 2 and rule 31, while manoeuvring promptly in a seamanlike way

So Blue must give Red room to keep clear of Blue and room to either tack or duck, if those are the seamanlike way to keep clear.

If Red chooses to duck she must give room to Green, overlapped to windward and on the inside, to pass the obstruction that is Blue (RRS 19.2(b). If Red chooses to tack Blue must give her room to hail for room to tack, and for Green to respond before Red can tack (see RRS 20).

Blue may not like it, but unless she is far enough ahead to tack and cross well ahead then Green is in control of the situation!

Blue is not the ROW boat throughout this scenario.  Blue is initially clear ahead of Red & Green and ROW.  When Blue luffs from her close-hauled course to HTW she is still the ROW boat and limited by rule 16.  At the moment that Blue crosses HTW and until she completes her tack, she is a keep clear boat w.r.t to Red & Green by virtue of rule 13.  As Red & Green obtained the ROW due to the actions of another boat they are not subject to the limitations of rule 15.  At the moment that Blue completes her tack rule 13 no longer applies and Red & Green are required by rule 10 to keep clear of Blue.  As Blue acquired the ROW as a result of completing her tack, she is subject to rule 15.

John is absolutely right 13, 15 and 16 are all of interest.   Now the key is to interpret “initially” as it is used in 15.

By definition room is: "The space a boat needs in the existing conditions, including space to comply with her obligations under the rules of Part 2 and rule 31, while manoeuvring promptly in a seamanlike way."
So at least for some period of time, Blue must allow Red to comply with her obligations under Part 2, which includes RRS19 room to pass an obstruction, i.e. that if Red ducks, she must also allow Green to duck.

If it is the premise that once Blue completed her tacked, that it was impossible for Red to bear away enough (in a prompt and seamanlike way) to also allow Green to duck, then I do think Blue as broken 15, because Red is immediately unable to comply with 19.   It's not a matter of seconds, it is a matter of possibility or not.

HOWEVER!!!! 

If Red was unable to give Green room to duck Blue, then it is exceedingly unlikely that Green would be able to duck Blue with or without the presence Red.  I.e. if Green could duck Blue, then Red should be able to do so and give her room.

Thus if the reason that Green had to tack away was that she couldn't duck blue, then it has nothing to do with Red being there.  Blue didn't break 15 because Green was able to tack to keep clear.

So I think the situation that has Blue breaking 15 is not actually possible, as it needs Green able to duck, but Red not able to do a similar manouvre.

Red can bear away and Green can tack so both can easily keep clear. 
If Red or Green invoke Rules 20 or 19 and fail to keep clear you cannot say Blue has not given room. Blue cannot be responsible for Red or Green making a bad choice of keep clear action.
 

Thanks for all the comments. To answer my original questions.

At position 2 Blue can tack and complete its tack. But Blue once on Starboard must give Red and Green Room to Keep Clear(Rule 16). There is no requirement in the rules for Red to have the opportunity to tack or duck. 
Since there is no time to hail to tack (Rule 20), when Red ducks, there must be room for Green to pass astern of Blue as it is an obstruction to both of them (Rule 19). 

Blue has fouled Red because Red does not have the Room to comply with her obligations under the rules of Part 2 and rule 31, while maneuvering promptly in a seamanlike way. (Case 11). It doesn't matter that Green can tack out. The obligation is on Blue to give Green room.

Tyler, 
I can't imagine a situation where Green is able to duck Blue, but Red is not able to give Green room to do so.

If Green can get down far enough to duck, then surely Red can do so too. If Green and Red turn away by the same angle, and Green clears Blue, then Red also clears Blue and gives room for Green to do so. If Red can't turn down enough without her stern hitting Green, then Green want keeping clear in the first place.

If Green is unable to duck Blue, then it is not because Red did not give her room, but simple because she was unable to do so. But she was able to keep clear of Blue by taking, so no foul.

Cheers

PS. you said 16 (changing course) in your message, then i think you meant 15 (acquiring rights).

The rules do not give green the right to choose a keep clear option (ducking) which benefits her progress around the course but requires additional room over an option (tacking) which hinders her progress around the course but enables her to keep clear.

Blue only has to give room to keep clear and no more.

The rules main aim is safety by avoiding contact. They are not about preserving a boats rapid progress round the course.

Yes, Blue has not directly fouled Green since Green can tack to keep clear. However, at Position 3, Red has an obligation to Green (case 11) as Blue is now an obstruction to both of them (Rule 19). Red must give Green to pass astern of Blue (case 11). Since Red can't, Red has fouled Green.
Since the reason Red can't give room is because Blue just tacked. Then Blue has failed to give Red room as it is defined.

Room: The space a boat needs in the existing conditions, including space to comply with her obligations under the rules of Part 2 and rule 31, while manoeuvring promptly in a seamanlike way.

Unless I am missing something, Red fouls Green but is exonerated. Blue fouled Red.

Tyler, i come back to asking in what situation could red not be able to give room to green, yet green can still duck Blue?

If Green is able to bear away to duck Blue, then why can't Red?

So in your situation, could Green duck Blue if Red was not there? If so, why can't Red not just sail parallel to Green and thus give her room?

They are identical boats, each with exactly the same notice of a new obstruction (blue competing her tack). Both can bear away equally and as much as the design of boat is able to.

How can it be that Green can duck but Red can't give her room?

I'm not saying that.
I'm saying that Red can duck Blue but cannot give Green room to duck as well. Hence why Blue has fouled Red.

I simulate three options: A) Red tack, B) Red Duck and Green Duck, and finally C) R Duck and Green Tack.
I suppose that green and red ar overlap by 1/2 lenght of boat, that Blue is 1/2 length over Red, and that 1 length are bettwen each boat on side.
A) Red tack, and Green have to tack the same, but i think that these three boats collide after.
B) Red bears down behind blue and Green does the same. It appears that green has no difficulty passing behind Blue. Red as no difficulty to pass behind Blue without beeing acrobatic, but must anticipate the tack of Blue to do so.

C) Red bears down behind Blue, and Green tack under Blue. It appears that Green will have contact with blue.
I made these tree situation for illustrate my observartions.
I find that without knowing the precise facts, it is difficult to conclude.

Pierre, thanks for the diagrams.   However, the diagram for scenario B) does not match your description? Instead it is for  Red ducks and Greeen tries to cross.

In your tacking scenarios where you say there is a collission with Blue, do you think the boats have competed their tacks?   As this happens outside of the zone, Blue would become keep clear boat and have to luff in some scenarios, albeit very late.

I think the tacking scenarios are more difficult if they happened in the zone, as they then cannot force Blue above a close hauled course.

Greg,
in diagram B) i illustrate that Green who is about one and a aft or two under Blue à moment #3, Green don't have to duck under Blue, he can pass behind Blue easily. and no collision occur.

In illustration A and C, collision occur in the zone, and at the instant #4, where Blue is now full on starboard.

In A) i see that Red has not anticipate that Blue tack fron instat #2 to #3, and he can't dock under Blue; he has to tack instantly, and cant call Green, he dont hab=ve time to do. The only chance for Red to dont collide with blue is to duck immediatly after moment #2 when he see that Blue start his tack, it's an for about less than one or 2 second???

for these 3 options, for me Blue tack too close.... But in B) we see that it is possible that Green and Red dont collide... If Red anticipate the action of Blue just after instant #2 and before instant #3.

But in regard of the illustration of Tyler, I observe that Blue is more further from red... about 1,5 square for Tyler and just one for my illustration. In my 3 illustration Blue complete his tack juste at moment #4. Other differences, the speed of Green and red after moment #2???

In second figure of Tyler, Green stop, and Red double his speed??? Iknow that details who change all the problem.

My take away from this discussion is that, despite years of review and revision, the RRS have not achieved the aim of promoting orderly sailing because there are too many possible interpretations of even a simple scenario.  

I think there is a simple answer to the original question, but it involves R 19 and possibly R 20, which create obligations.

My simple view is that while Blue is tacking she is subject to R 13 and is keep clear boat. When the tack to stbd is complete, she becomes ROW and R 15 applies as ROW changed.

Under R 15 the room to be given is for the affected boat(s) to be able to keep clear. The definition of room includes any obligations under Part 2 and R 31.

As Blue is now an obstruction, R 19 applies and Red gets to choose which side to pass Blue. If Red chooses to pass astern of Blue then room has to include room for Green to pass astern too – that is an obligation on Red.

If Red hails for room to tack, then R 20 is invoked, then room has to allow for the affected boats to stay clear based on the options of R 20 – and again that creates obligations.

John

In this image from the OP, it is suggested that Blue is breaking 15 as they do not allow Red to give room to Green to pass an obstruction by 19:

Yet Green has born away a lot more than Red.  We are told they are identical boats, if Green can get down to pass Blue (close in this image), than so should Red.  Indeed if this image was altered so that Red sails parallel to Green, then room is given under 19 (still debateable if Green makes the duck or not, but she had the option to tack).

I see no infringement of 15 by Blue here.

With regards to Robert,   the lack of clarity in this discussion is not so much about the RRS, but more about how difficult it is to capture, describe and communicate scenarios - even ficticious ones.  If "facts can be found" accurately, then the interpretation of the rules is more often than not pretty clear.  This difficullty will exist with any set of rules that you want to come up with: skiipers at the helm, witnesses on the water, judges in the room and pundits on the forums will mostly struggle to find a consistent set of facts rather than to apply the rules to those facts.  For example,  it's more often not that boats don't know that the rules that inside boat has rights at a mark, it's that they disagree if there is an overlap or when it was established.     It is not the RRS fault that the sport is inherently subject to biased points of view, false perspectives, faulty recall and innacurate estimations of time/distance/velocity/heading.

Sure the more concepts that go into a set of rules (overlap, astern, windard, tacking, overtaking, rounding, zones, manouvering, etc.) then the harder it is to establish the pertinant facts for those rules.    So keeping things to a minimum is important.    But I think the RRS do a good job of that as you get your basic keep clear rules from just 4 concepts: Port, Windward, Astern, Tacking and the General limitations are established by just 4 more: Contact, Acquiring rights, Changing course and Proper course (and it's never 17 unless blantently so).  Any set of rules governing sailing (let alone racing) is going to need to have a similar number of concepts.  The Colregs are very similar in their basic rules, but have more issues with the need to determine the motiv force of a vessel and sometimes it's navigational purpose.  The RRS are far from perfect, but to lay disorderly sailing at their feet is asking too much of them, at least while people are involved!




 

In that diagram Greg, Blue doesn't reach CHC until 3 and red and green are bearing away while Blue is still subject to Rule 13. Blue breaks Rule 13.

Blue doesn't become an obstruction until she reaches CHC as a boat racing is not an obstruction  unless they are required to keep clear of her or, if rule 22 applies, avoid her.  Green is bearing away into Red breaking Rule 11 and during this time Rule 19 does not apply so she cannot be exonerated by Rule 43.

If Red and Green hold course, it's possible Blue will break R15 unless Green can tack and Red can bear away.

Richard, re: “Green is bearing away into Red breaking Rule 11 and during this time Rule 19 does not apply so she cannot be exonerated by Rule 43.”

Have you considered Rule 43.1(a) exoneration for Green?

Monkey wrench:
Blue is required to keep clear before CHC, but if she is not keeping clear, she becomes an obstruction under the rules.

I think that many people are missing a key point.
Once Blue has reached a close-hauled course she acquires right of way, and must initially give room. She becomes an obstruction to Red and Green.

When Blue becomes an obstruction the Red as right of way boat may choose which side of Blue to pass (RRS 19.2).
If she chooses to duck she must give Green (overlapped to windward) room to pass between her and the obstruction.Green has no obligation to duck and take the romm to which she is entitled.
If she  chooses to tack she must hail for room to tack and both Green and Red must follow RRS 20.2.

I don't think this is a question about 13. If Blue doesn't keep clear of Red whilst tacking, then it does not matter if Green is there or not. So this wouldn't be a 3 boat question.

To make this a question about 3 boats, let's assume Blue does complete her tack in just enough time for Red to start taking action and duck her in a seaman like way.  I.e let's assume that Blue doesn't break 15 with Red.

With those assumptions, the OP was asking should Blue also be obligated by 15 to give Red enough room so that she can give Green room by 19?

I think the answer is yes, but only if Green is able to duck Blue if Red was not present. If Green can duck Blue but Red does not give her room, then Red is breaking 19 by not bearing away enough. Is that the fault of Blue breaking 15?. Look at the diagram that the OP posted and you can see that Green turns more than Red. Why didn't Red turn more? That's not because of Blue as she is in the other side. Red breaks 19 all on her own, not because Blue didn't give her room to do so.