Grant, I’m having a tough time making sense of the dotted track lines and the colors of the boats. Boats seem to be changing colors. - Ang

I have clarified by amending the post. Does this help?

Your colours are really distracting. The green boat at position 2 is not allowed to sail above their "proper course - per Rule 17".  But this obligation does not remove the obligation that Red2 has from needing to keep clear of Green2.

So Green2 has the right to luff Red2 but Green2 may not sail above their proper course.  The proper course of Red2 is irrelevant and Red2 must keep clear of Green2.  If Red2 thinks that Green2 is sailing above their proper course, then Red2 should protest Green2, but Red2 must still keep clear.

At position 3, the proper course of Green3 is irrelevant, Green3 has to give Red3 mark room - Rule 18.

So
At Position 2 - Rule 17 applies to the Green boat and Rule 11 applies to the red boat
At position 3 - (and actually when Red 3 reaches the zone) - Rule 18 applies

Regarding rule 15/16 and room to keep clear, if there was no contact and you didn't have to do any unseamanlike maneuvers, then this implies that you were given room to keep clear.

The diagram makes no sense.  Between position 1 and 2 Green changes to Red, and Red changes to Green.

Grant re: “To explain where I am confused, here is another interpretation of Rule 17 popularly quoted:....”

I’d suggest you forget this popularly quoted interpretation.  If you rely upon only RRS 17, does your confusion disappear?

Hi Grant,

                "The changing hull colors indicate the boat with right-of-way (green) and not (red). The dotted line indicates the
                 course of both boats"

From the quote I interpret that the boat clear astern at position 1 in your diagram, is the same boat that is leeward ROW at
position 2. For clarity sake it might be easier to disregard the colours and refer the boat clear astern @ position 1, as boat A and the other as boat B.

At position 2, boat A is ROW leeward but subject to rule 17 which limits the course she may sail while overlapped with B, 
to her proper course. B however, must keep clear if A sails above her A's proper course because it's possible for both boats to be penalised - if A sails above her proper course breaking rule 17, and B fails to keep clear breaking rule 11.[Remember B would not have been compelled to break 11, because she could have luffed to keep clear].

When the first of them reaches the zone between positions 2 & 3, rule 18.2(b) begins to apply and A must give B mark-room which includes;
            Mark-Room (a);  room to sail to the mark when her proper course is to sail close to it,
Room to sail to the mark means just that - the space a boat needs in the existing conditions, manoeuvring promptly in a seamanlike way, to sail directly to the mark if that's her proper course.

That means that, if from the instant (B) enters the zone, A prevents B bearing away to sail her proper course to the mark, A breaks rule 18.2(b), and if B breaks rule 11 by not keeping clear, she is exonerated by rule 43.1(b). A is still ROW, but she must not prevent the inside overlapped boat from sailing directly to the mark.

In my experience, a lot of sailors make the mistake of believing that, in scenarios similar to the courses sailed by the boats in our  diagram, the outside boat has given mark-room simply because the outside boat eventually bore away to allow the inside boat to round the mark. But such is not the case. The inside boat must be allowed to sail her proper course to the mark from the moment the first of them [it could be either boat] reaches the zone as required by the first part of the definition (a). The right to round and pass marks is contained in the second part of the definition - part (b).

Thanks for your comments. To avoid further confusion, I have changed the colours of the boats so that each boat maintains the same colour.

Does this further tweak/clarification change your positions on the rules?

“To explain where I am confused, here is another interpretation of Rule 17 popularly quoted:....”

See Definition of "proper course":"...  A boat has no proper course before her starting signal."

Hi Grant,

No, it doesn't change my assessment, but it will make it easier for others to read.

Yellow is limited by 17 to sail no higher than her proper course between becoming overlapped to leeward of Blue and Blue reaching the zone.

From the time Blue reaches the zone, Yellow must not prevent Blue from sailing her proper course to the mark.

Phil.

Thanks, Phil. That makes perfect sense.

Making discussion short.
Pos.2 both yellow (17) and blue (11) DSQ
Pos.3 yellow (18.2b) DSQ

About rules and comments, I agree with Phil

though, blue seems responding to the luff of yellow.. and Yellow, when get ROW for 11 and immediately luffed... 15?? Is there a contact?

I might not DSQ blue. Might. 

@Aldo, as I can see, there is a contact jib/hull in pos. 2. If not... blue is safe

@Luigi, there is no contact between the boats.

@Aldo, blue avoided yellow simply to avoid a collision. The overlap was gained when a gust hooked the bow of yellow to starboard towards blue's stern. It was a near miss. When I yelled "room", the skipper of yellow yelled "luffing rights" and proceeded to taunt my stern.

I found this diagram on the Allens website. The large bold numbers refers to the rules.

How does this diagram relate to the proper course rule? 

In the Allens pic above, RRS 17 does not apply at #3 (or at #2 when RRS 17 is tested).  In this case Red is from clear astern to an overlap to windward of Green, not to leeward. 

Proper course does not have an application in the scenario above, given only the facts in this drawing. 

Re Grant's diagram:

@2, Yellow has ROW and Blue is required to keep clear. Rule 17 is on but Yellow could claim that sailing high of the mark and planning to bear off or gybe to it is her proper course. However, as Yellow luffs she must allow Blue room to keep clear. Since Blue is well advanced on Yellow, Blue can't come up without swinging her stern towards Yellow's bow. So I'd say that Yellow's luff is constrained mainly by her rule 16 obligation.

If there's contact at that point without damage or injury I think both would be exonerated. Yellow has ROW and Blue is sailing within room (to keep clear) that she's entitled to.

As they enter the zone Blue becomes entitled to mark room. @3 Yellow isn't obligated to "hold her proper course" (and could still argue, up to a point, that sailing high of the mark is her proper course) but she is obligated to give Blue room to sail to the mark and round it. From the dotted line track it looks like Yellow did respond to Blue's turn toward the mark so I think no rule broken. 

It appears both boats gybed to the mark after position 3, in which case Blue becomes leeward ROW and still entitled to mark room after both gybes.

yellow will have hard time to convince me she was on proper course