Mark it's a tricky situation, especially if you have at least any of the two classes racing on a course together. 
The introduction in the RRS clarifies that when rules of an appendix apply, they take precedence over any conflicting rules in part 1-7 and the definitions, but it is silent on the conflict of rules between appendices. 
So, we could consider the board closure to the mark to decide the size of the zone (as per its appendix) to then apply the RRS 18.

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 :-)

I don't think this is quite right.  It is making a RRS 2 protest look like a RRS 69 hearing which it is not.

I agree that a breach of RRS 2 that affects the fairness of the competition on the water will usually be accompanied by a breach of Part 2, but even if it is not, a breach of sportsmanship that affects the fairness of the competition is nevertheless an incident in the racing area and requires a hail of 'protest' and if necessary display of a flag.

Agree, and in OP case, I think we have

Boat B broke RRS 2.  RRS 36(b) does not exempt a RRS 2 breach.  On valid protest B should be DNE.