John A .. yes .. my comment regarding 18.3 (thanks for pointing out typo) assumed that they were fetching the mark after the 2nd tack from port to starboard. 

On your other point .. I don't think it's so clear that Red would still be sailing within the MR she is entitled to at the edge of the zone.  I never suggested it was a direct corridor from when she entered the zone. 

I can definitely see and appreciate both arguments. 

PS: I think we all agree that a MR entitled boat can simultaneously be in the zone and outside of the MR she is entitled to. 

 Let's place the boats in the top-left quad (the pie slice from 9-12).   Is your answer the same? (That she can luff up so quickly that she breaks 16.1 and is exonerated). 

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 :-)