When they tack to stbd, 18.2(b) swich off mark room but Red still protected by 18.2(c) as an inside boat

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 starboard 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 :-)