“However, a boat racing is not an obstruction to other boats unless they are required to keep clear of her or, if rule 23 applies, avoid her.  A vessel underway, including a boat racing, is never a continuing obstruction.”

2- If O contacts L, O fouls L by not keeping clear under Rule 11.
3- If L alters course to avoid contact with O, a protest made by L against O under rule 11 would be successful.

The boundary is a continuing obstruction. Does 19.2(c) enter into it between L and O (Blue and Green, respectively)?

In the original diagram:
At 1, O is clear astern and required to keep clear of L
At 2, O becomes overlapped between L and the obstruction. Is there room for O to pass between L and the obstruction? (check the definition of room)
At 2, what is the situation between W and O (Y and G) with respect to ROW and entitlement to room?

Does the scenario change if Y and G are both faster than B (and G is faster than Y), thusly:

It is an odd perversion to conclude that W(yellow), unable to keep clear, is not "an object that can be safely passed on only one side,"

1. when Yellow and Blue first reached the continuing obstruction, Yellow was entitled to the 19.2(b) room inside of Blue
2. that the proper course for Yellow between positions 1-4 is not to fall-off to leeward and sail away from the wall (this removes questions regarding rule 17)

1. At Position #1:
   1. Yellow is windward, overlapped with Blue 
      1. -> Yellow must keep clear of Blue via rule 11
   2. Green is clear astern of both Blue and Yellow 
      1. -> Green must keep clear of Blue and Yellow via rule 12
   3. Yellow is inside overlapped with Blue at the closest edge of a continuing obstruction 
      1. -> Yellow is entitled to room from Blue to pass between Blue and the obstruction via rule 19.2(b) (and see preconditions)
   4. Because both Yellow and Green must keep clear of Blue, Blue is an obstruction to both Green and Yellow (but Blue is not a continuing obstruction)
2. At Position #2:
   1. Green becomes overlapped to leeward and outside of Yellow relative to the continuing obstruction
      1. -> Green is now ROW and Yellow must keep clear of Green via rule 11, and 
      2. -> Green must initially give Yellow an opportunity to keep clear via rule 15 (which Green does).
      3. -> Green being outside overlapped with Yellow, must give Yellow room to pass between her and the obstruction via 19.2(b)
   2. Green is still clear astern of Blue
      1. -> Both Green and Yellow must keep clear of Blue, therefore Blue is still an obstruction to both Green and Yellow.
3. At Position #3: 
   1. Green becomes overlapped to windward of Blue
      1. -> Green still must keep clear of Blue, but now under rule 11  rule [19.2(c)] instead of 12
      2. -> Blue continues to be an obstruction to both Yellow and Green, as both [Yellow] must keep clear of Blue via rule 11, [Green via 19.2(c) (see below)]
   2. Since the time the overlap began with Green at position #2, Yellow has not been able to give Green room to pass between Yellow and Blue, Blue being an obstruction to them both
      1. -> Therefore, Green is not entitled to room from Yellow to pass between Yellow and Blue via 19.2(b)
   3. Blue must give Green room to pass between Blue the continuing obstruction via 19.2(b)
      1. -> Yellow must keep clear of both Green and Blue
         1. -> Yellow is not an obstruction to either Green or Blue, therefore
         2. -> The 19.2(b) room Green is entitled to from Blue does not include room to pass Yellow as Yellow is not an obstruction and is not part of the continuing obstruction (Phillip .. note this one!)
         3. Absent Yellow, Blue is providing Green plenty of room to pass the continuing obstruction.
   4. At Position #3, there is not enough space for Green to pass between the CO and Blue 
      1. -> use test of freezing Blue in position and progressing Green and Yellow forward in their relative places
      2. -> Green must keep clear of Blue, 19.2(c) applies between Blue and Green relative to the CO 
      3. -> Rules 10 and 11 no longer apply between Green and Blue as long as they remain overlapped
4. At Position #4 (+ Conclusions): Green continues without changing course, contacts Yellow and Blue bares away to avoid contact with Green, no damage or injury
   1. Green does not alter course and makes contact with Yellow 
      1. Yellow failed to keep clear of Green, a boat to leeward, and broke rule 11
      2. Yellow is exonerated for breaking rule 11 by rule 21(a) because Yellow was sailing within the 19.2(b) room she was entitled to
      3. Green, the outside boat at an obstruction, failed to give Yellow room to pass the obstruction, despite being able to do so since the overlap began, and broke RRS 19.2(b). (NOTE: Yellow's room to pass between Green and the obstruction included space for Yellow to comply with her obligations under rule 11 and 14)
      4. Green, the right-of-way boat, did not act to avoid contact when it became clear that Yellow was not keeping clear.  Green broke RRS 14
   2. Blue alters course to avoid Green
      1. Green failed to keep clear of Blue, a boat to leeward, and broke rule 11
      2. Green, an inside overlapped boat at a continuing obstruction not entitled to 19.2(b) mark-room, failed to keep clear of Blue, the outside boat, and broke Rule 19.2(c)

Please explain how Yellow, unable to luff into the continuing obstruction, can keep clear of Blue who establishes a tight leeward overlap from astern.

1. I mis-applied the colors. I meant:
Please explain how Yellow, unable to luff into the continuing obstruction, can keep clear of Green who establishes a tight leeward overlap from astern.
2. I would urge you to read 15 and tell me when Green has begun giving yellow an opportunity to keep clear.

1. Green becomes overlapped to windward of Blue
   1. -> Green still must keep clear of Blue, but now under rule 11  rule [19.2(c)] instead of 12
   2. -> Blue continues to be an obstruction to both Yellow and Green, as both [Yellow] must keep clear of Blue via rule 11, [Green via 19.2(c)] (see below)
2. Since the time the overlap began with Green at position #2, Yellow has not been able to give Green room to pass between Yellow and Blue, Blue being an obstruction to them both
   1. -> Therefore, Green is not entitled to room from Yellow to pass between Yellow and Blue via 19.2(b)
3. At Position #3, there is not enough space for Green to pass between the CO and Blue 
   1. -> use test of freezing Blue in position and progressing Green and Yellow forward in their relative places
   2. -> Green must keep clear of Blue, 19.2(c) applies between Blue and Green relative to the CO 
   3. -> Rules 10 and 11 no longer apply between Green and Blue as long as they remain overlapped
4. At Position #4 (+ Conclusions): Green continues without changing course, contacts Yellow and Blue bares away to avoid contact with Green, no damage or injury
   1. Green does not alter course and makes contact with Yellow 
      1. Yellow failed to keep clear of Green, a boat to leeward, and broke rule 11
      2. Yellow is exonerated for breaking rule 11 by rule 21(a) because Yellow was sailing within the 19.2(b) room she was entitled to
      3. Green, the right-of-way boat, did not act to avoid contact when it became clear that Yellow was not keeping clear.  Green broke RRS 14
      4. Green, the outside boat at an obstruction, failed to give Yellow room to pass the obstruction, despite being able to do so since the overlap began, and broke RRS 19.2(b).
   2. Blue alters course to avoid Green
      1. Green, an inside overlapped boat at [passing] a continuing obstruction not entitled to 19.2(b) mark-room, failed to keep clear of Blue, the outside boat, and broke Rule 19.2(c)

1. 1. Blue alters course to avoid Green
      1. Green, an inside overlapped boat at a continuing obstruction not entitled to 19.2(b) mark-room, failed to keep clear of Blue, the outside boat, and broke Rule 19.2(c)

 Green is not "at a continuing obstruction".   Yellow can not be a continuing obstruction. 

• 19.2(c): " While boats are passing a continuing obstruction, ...".   I will go back and edit that after I submit my comment here.

• 19.2(c): " While the boats remain overlapped, she shall keep clear and rules 10 and 11 do not apply"