My first cut on position 3 is that Blue while tacking failed to keep clear of Yellow, breaking rule 13. Both boats broke rule 14, Yellow is exonerated as ROW boat. 

At 5, either Blue took more mark room than she was entitled to or Yellow failed to give sufficient mark room so somebody broke rule 18 but would need more information to decide who. Plus the rule 14 issue obviously. 

Any "protest" hails? Where, when?

Tim!!!

Thanks for that.  To spice it up, I have edited the original facts. See Fact 2.  Sorry!

Mr. Lancaster - Consider the protest was valid!

Position 5 as mentioned depends on the conclusion as to whether Blue took more or just the right amount of mark-room.

The interesting one here is Position 3.

To be devil's advocate for Blue, was there anything that might have caused them to round wide, such as current, or large waves?

"A nanosecond before" still makes it look to me like it was reasonably necessary for Yellow to alter course to attempt to avoid contact, which she was unable to do. I'd stand by my original conclusion at position 3.

The complicating issue at position 3 to me is that Blue, briefly, as soon as they're both on the same tack (which is to say, after Blue passes head to wind, not when she completes her tack) becomes entitled to mark room. But mark room doesn't include room for Blue to tack back onto port so I'm not sure it's relevant. 

Is that the complication you're looking at? Seems like Blue might claim exoneration for rule 14 but I'm not sure she'd get out of rule 13.

Tim,

Yes..this is along the lines

By inserting Fact 2, I'm trying to invoke Rule 18, but not with anything to do with tacking.  That to me is the interesting discussion to be had.

At position 3 blue has broken 13. Mark room does not include room for her to tack. At 4 and 5 yellow has not given sufficient room. Mark room at 5 does include room to tack

Right-O!

Thanks for the suggestions.  Charles, I think you're right (along with the others) as the original diagram shows it.  Blue is not forgiven for a breach of rule 13, since mark-room does not include room for her to tack in this instance, since she would not fetch the mark after.

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The original diagram did not quite depict then the situations I'm trying to invoke.  So with you're forgiveness, I'll adjust once more.

Here's another try.
DIAGRAM 2

Facts Found: 

position 3 blue RRS 15 and RRS 14 for both (exoneration for Yellow), position 5 RRS 18.2a for yellow she don't give sufficient mark-room to blue, again RRS 14 for both (exoneration for Blue)

In either diagram, at position 2, Blue has broken rule 10, 13, or 15 (take your pick) as well as 14 possibly for both.  (Here I continue to have a problem with 'need not anticipate' because some judges seem to ignore it, or at least interpret the time needed to respond differently.)  Case 9 allows Yellow, the  starboard tack boat, to choose to sail past the windward mark, which is what she appears to be doing until she has to alter course in an attempt to avoid a collision, or at least reduce the impact of that collision (Case 50 would seem to be applicable).  If you want to go to Rule 15, whether the time between Blue acquiring right of way and contact was a nanosecond or two seconds Blue did not give Yellow time to keep clear.  
Rule 18 switches off while both boats are changing course and tacking, and 18.2 (a) switches back on when they are both overlapped on the same tack.  At this point Blue (windward) must keep clear of Yellow, but is entitled to Mark-Room.  In diagram 1 I would find that Blue had taken more room than required, in diagram 2 I'm more inclined to say that Yellow had not given Blue Mark-Room.
But I'm only one of three, or more, determining those facts...

I agree that in the new diagram at position 3 Blue breaks 15. Blue gains ROW as soon as she completes her tack but if contact occurs "a nanosecond" later she has not initially given Yellow room to keep clear. I don't think Yellow breaks rule 14 as it's not reasonably possible for her to keep clear from the instant that Blue gains ROW, and Blue breaks 14 but is exonerated as she's clear ahead ROW.

Just after 2, when Blue passes HTW and the boats are on starboard tack, Blue becomes entitled to mark room. This entitlement ends between 3 and 4 when the first boat passes HTW from starboard to port but Blue's entitlement is re-established when both are again on port.

In this scenario Blue is entitled to mark room to tack since she is overlapped inside and to windward and will be fetching the mark after her tack, so the "corridor" that Blue is entitled to does include room for her stern to swing through the tack. In the new diagram I think at 5 Yellow has broken 18.2(a). Both break 14 at 5, both exonerated (Yellow ROW, Blue sailing within her mark room)

Seems clear to me that Blue broke rules 13 and15 at position 3, possibly rule 10 as well.  It appears the Blue broke rule 13 a second time at position 5.  Unless there was damage or injury, I think that Yellow would be exonerated both times under rule 14.

Tim, I agree with your first paragraph, though Blue's exoneration on 14 is moot because we've already decided she broke 15.
To your second paragraph, the pedant in me will say that Blue doesn't become the inside overlapped boat until she is on a close hauled course, rather than immediately after passing HTW (13).  At that point Yellow has to tack (or take some other action) to give mark room to blue, to sail to the mark, which she does; and Blue tacks to sail to the mark. Although while tacking she is subject to 13, she does appear to keep clear of Yellow.  Diagram 2 at position 4 suggests (I hope) that Yellow (sails flapping) hasn't yet reached a close hauled course, rather than she is luffing Blue.  
To Tim's third paragraph, I'd suggest we look at Blue's course between 4 and 5.  I read that as Blue's course clearly dropping to leeward, although Blue appears to have room (at 4) to round the mark without contacting it. So, John Thorne, at position 5, I'd suggest that as Blue hasn't yet reached (or gone beyond) HTW 13 doesn't apply and the contact breaks Rule 11.  But that's only my opinion.  Tim's view varies at this point, and we would discuss, given the conditions, the size and manoeuverability [pls excuse the BR Eng ;) ] of the boats, so it may be that we decide that Yellow broke 18.2(a).

I'm not sure I agree. When Blue and Yellow pass HTW at about 3.5 they're overlapped (neither is clear astern of the other) and since Blue is to port of Yellow at a mark to be left to port she's the inside boat. Maybe not instantaneously when Blue passes HTW but as soon as her stern swings enough that Yellow is not clear astern. That would occur well before Blue reaches close-hauled.

Thanks all for a good discussion.

I'll be honest; I was testing a hypothesis, but fortunately failed to create the scenario.

Most people here are happy and in agreement with the Position 5 contact.  To reach a decision would need further investigation, but two possible outcomes generally prevail.  They are either that Yellow broke rule 18.2a by not providing room for Blue to tack, or that Blue took more room than she was entitled and broke Rule 11.

So I'll not go further into Positions 4 or 5.

In Position 3 (the main point of this thread), I was aiming to test "whether there is a time where a boat's movements well below the port and starboard laylines, are protected under her right to mark-room if it applies, in so far as sailing close-hauled on either tack is consistent with 'sailing to the mark'."

In actual fact, per the two diagrams I presented, I don't think either Blue's actions were protected.  Here's my summary.

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Position 2/3

When Blue passed HTW, both boats were on the same tack in the zone.  None of the 18.1 exceptions applied.  Rule 18 applied, and Yellow was required to give mark-room to Blue per 18.2(a).

Position 3 - Diagram 1

Blue has completed her tack to leeward of Yellow.  Given that they were overlapped at that moment, it is very probable (if not geometrically certain) that Blue broke Rule 13.

Blue was entitled to mark-room after passing HTW, but that did not include any room to 'tack' since she is/was neither overlapped to windward of Yellow nor would her tack end up fetching the mark.  Thus, Blue would not enjoy exoneration for breaking Rule 13.

Position 3 - Diagram 2

Blue has completed her tack clear ahead of Yellow, but broke Rule 15.  Since the boats are not overlapped, she is not entitled to any mark-room per 18.2(a) at the time she acquired RoW under Rule 12.

Thus, Blue would not enjoy exoneration for breaking Rule 15.

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So back to the drawing board in my quest.

Thanks!  Good discussion.