John's analysis is, I think, a correct reading of the rule.  Angelo suggests that if the red boat cannot sail to the mark on starboard tack, then she is not entitled to room to sail to it, and I think that's how many sailors interpret rule 18.2, even though the rule itself doesn't support that interpretation.  I think that if the red boat in the original diagram were to luff sharply and hit the blue boat, the blue boat would protest under rule 16.1 and quite probably win in the protest room.  

I don't understand Angelo's distinction between his scenario and the original one.  In both cases, the inside boat is unable to pass the mark on the required side without tacking, so if she can't be exonerated for breaking rule 16.1 in Angelo's scenario, why can she be so in Catalan's?

Niko .. let me get this straight.  The class in question has a jib boom (self-tacking setup).  What we are asking to do is not attach anything to the sail .. but to attach to the jib-boom at some location along the jib-boom to hold it out down-wind?

I know several boats that do that with a hydraulic piston that they buy at an auto parts store (same piston that holds open your hatchback.  The anchor one side of the piston on the centerline of the bow and the other somewhere along the jib-boom.  It does a nice job and if sized and installed correctly ... it doesn't put up a fight when tacking or gybing to get the boom across.

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