Green

My take on this is that Yellow has a problem under rules 11 and 12.
When Green establishes her overlap on Pink at position 2 Pink is then no longer an obstruction to both green and yellow as 'THEY (Green and Yellow) are no longer required to keep clear of her (Pink)' - last sentence of Definition 'obstruction,
The old disappearing obstruction problem.
Therefore Yellow cannot claim room under 19 and must simply keep clear of Green under rule 11 and Pink under rule 12.

From positions 1 to 3, Green is altering course.  When Green alters course, does Yellow have room to keep clear of Green, which would include room for Yellow to fulfill her obligations with regards to Pink?

Murray,
In my opinion yes. She does not become overlapped with pink until position 3 and small dinghies in the conditions described can easily luff and slow.

Maybe WS Case 117 would be helpful for your questions....

Y fails to keep clear of G under RRS 11. P did not break a rule because Y failed to give P room to keep clear under RRS 15. Y is therefor not exonerated under RSS 43.1(a). G did not break a rule since it gave Y room to keep clear. Y DSQ. 

John S re: "small dinghies in the conditions described can easily luff and slow."

OK ... how about if we swap them for 9,500lb (w/crew) 10m  J/105's traveling at 6kts in 12kts of breeze?

In that case, as G alters course at #2 does she provide Y room to KC of Pink under 16.1?

How does the new 14(b) factor in?

Full agree with john

Angelo,
Same rules. As Stavros says see case 117.
Yellow needs to think ahead and not go there! 

John S and Stravos .. IMO though Case 117 is informative relative to RRS 19, it is significantly different than the OP.

Case 117 has the 2 boats approaching the line of boats from clear astern with L apparently holding course.   There is no discussion of the leeward boat changing course and the case makes no mention of RRS 16.1.

In the OP, we have the 2 boats "reaching along the sterns" and then Green alters course significantly to windward.

When Green does that at #1.5, look at Yellow vs Black and Pink.  Now .. look at the drawing below from Case 117 .. W has a clear space to luff HTW when L gets overlap with D and L does not alter course.

RRS 16.1 is in play in the OP and not in Case 117. 

We have to determine if Yellow may be trapped from responding to Green's course changes (as you inferred .. based upon the boats, maneuverability and momentum) .. where none of that is in Case 117.

At position #1 everything is hunky-dory.

Then sometime after #1 but before #2, G changes course.

My first instinct took into account Y's momentum after Gs course change.

The diagram shows that Y doesn't have much wiggle room here to avoid the stern of Black. She might have luffed into that space between D-Blue and Pink, backed her sail, wiggled her tiller hard, and put a drogue out and stopped her boat.  All that without causing D-Blue to need to luff (she can't) and without making contact with Pink. Then I would agree, that G's luff was fine.

If Y had tried all that but sailed into the back of Pink or forced D-Blue to luff into purple, then we would have to conclude she was compelled crash by Gs course change. Easy peasy. 

Well, Y had a lot of pace to wash off. From being over a boat length astern to overlapped in just one boat length, Newton would find that Y's speed was about a third faster than Pink.  I don't blame her for not trying that luff HTW.

What actually happened?

G and Y had to keep clear of P (rule 12). P was an obstruction . Case 117 reminds us that G needed to give Y room up until the moment G became overlapped with P (call it point X) and P no longer was an obstruction.

So at point X, G went from being clear astern to acquiring Right Of Way as leeward boat.  P went from being an obstruction to being a keep clear boat. Y goes from being entitled to room to go for the gap to having no rights to anything! 

It seems a little unfair to Y, no?

Between #2 and #3 G continues to change course. Not by much, but enough to seal the fate (contact) of Y. All the while she has no boat to leeward!

Had G bore away at #2 (or even held her course) Y would not have been the meat in a right of way sandwich and had to hit Pink.

We could / should and would debate the characteristics of the boats to decide whether Y's luff was an option and if we found so, penalise Y.   Quests are not as efficient as TP52s, but way more than Optis.  Being able to simply 'luff and stop' depends on the boat you're sailing.  Also, I admit, static diagrams are hard to use.  John makes a valid point that Y only overlaps P just before #3 meaning that Y had about a boat length to wash that pace off if she luffed.  Possible in some boats for sure.

I think Green here may have broken rule 16.1 between #1 and #2 and certainly after #2.

I think she caused Y to hit another boat, so is looking at the new rule 14(b).

Y broke 15 but was compelled to do so.

Here's an interesting question. If I conclude that Y was compelled to break rule 15 by G, did G also break rule 15? 

Well, food for thought.. 

Green looks in a bad position.

She relatively to the obstructions ahead can choose how to pass them.when she changes course she must give room, this is rom for the windward boat to comply with her obligations.
Green could easily be toast here..

I can certainly see a situation where Green could have problems.
It would depend on the 'facts' presented at the hearing.
There are clear differences between the diagram in this post where there is clearly space for both boats to get through the gap from position 2 and case 117 where there is only space for one boat.

But Yellow could have complied with her obligation  versus Pink by slowing down in time behind Pink. I therefore think that Green gave Yellow room to comply with her obligation versus Pink. 

A question like this is great since it generates good discussion.  It ultimately boils down to opinion.  There is no exact answer as I see it.

We can see a split emerging in this thread as a result... some think Y, some think G.  We may never get agreement.

Our opinions are shaped by our experiences on the water as sailors and observers.  The different kinds of boats we sail, and the different environments.  As John said, how we would decide this largely depends on how the scenario was presented in the protest room.

Reinhard thinks Y could slow down in 1BL.  Perhaps.  Perhaps not.

So long as the rules are clear and agreed, I don't lose too much sleep over trying to find an absolute answer.  This is what RRS 63.5(b) is there for.

Good discussion.  Thanks.

Ben ... also is a good example that Cases and local Appeals are based on a specific set of facts.   Alter a fact or a set of facts a bit and the case might not quite apply or other rules not in the case come swooping in. 

Here Case 117 was definitely helpful in describing what happens to RRS 19 as the overlaps and obstructions change, but in the OP scenario it will rest of RRS 16.1, which wasn't in the case. 

Here, for those of us who sail and race, we have probably had to make the decision between a blunt collision and a grazing one.  Do I T-bone Boat A or rub hulls with Boat B.  

It might come out the room that Yellow says, "Look I had nowhere to go, I had momentum, I was going to hit "somebody" the question was only who and how. I chose to put my nose between the boats because I thought it would cause less damage". (Pretty much my exact words several years ago) 

Agree .. it'll come down to the boat-specs, speeds, winds, and what is said.