Red is entitled to room to sail to the mark.

If she is not heading to or towards the mark, i think she is entitled to room to change course so as to sail to the mark

If it is not possible for her to do that without tacking, I think she is entitled to room up until she is heading to the mark, or passes head to wind, whichever comes sooner.

As shown in Angelo's diagram Red is not sailing to the mark, in fact she is sailing away from it, but she is still entitled to mark-room, that is room to sail to the mark, and as we've previously agreed, that is not a direct corridor from where she entered the zone, but it is a direct course from her present position to the mark.  I'm saying that she is entitled to room to change course onto that heading.

Robert "My review of RRS 86.1(a) indicates no issues with this change."

An argument against that assertion might be that 86.1(a) forbids changes to rules of an appendix that changes Part 2 and Def's and that doing what you suggest .. in effect ... changes those Appx-rules by inserting a "however-clause" exception and then inserts the standard language.  

What I am saying is that it is more complicated than simply having a gravitational force component parallel to the local surface of the water.  Surfing, as a general phenomena, is defined and understood.  Where it isn't defined is in the RRS.  Unfortunately, this forum is not the place for the very long and very deep dive explaining the physics of surging, surfing, and planing.  But to me, the take away is that we need to understand the difference between surging, planing, and surfing and when each of these is possible to be able to properly interpret and apply RRS 42.

Wow Paul ... that must have been a lot of work (and moving forward as the working out the kinks phase begins). 

Congratulations!

Ang

Thanks Ben ... yea .. you asked how the reasoning would go and I obliged :-)