Hi scooby -good on ya wouter -good beginning -

Historically rating systems have never lasted without being rethought and revised in different forms periodically ,-the best being one with the greatest simplicity able to renew and change with changes in the craft themselves over time.

Agree w scooob and will also wait for a less stressfull work day and be brief,-or is it holiday stress already ?,

to answer your question scooby ,- think what wouter meant in using the F-18 as a benchmark of sorts for rating is not a specific F-18 cat design but instead the measurement parameters that form the F-18 class used as a common model or benchmark of comparative speed.
Conceptually for consistancy and fairness in rating it is important to comprehend all craft as design measurement based rather than a specific boat by brand or class with huge variation in class brand rules ,-it only leads to inconsistancies .

Wouter has some great concepts in the attempt to rethink and update a design measurement based rating rule ,-

My 2 cents currently would be for the development of a combination rating system that would use the current yardstick pn with its attempt to equate real time to distance traveled in windspeeds in that same scale and familiar numbers , but used as a correcting factor to design measurement based dirived numbers though in more simplistic basic formula than Wouter is beginning to describe. Taking the approach of design measurement rating only historically leads to reinforcing current trends in design, thus the need for only basic definition in the design measurement aspect of L W SA plus beam and basic crew spin jib relativism ,--adding a yardstick system in combination should correct any major errors or omissions in the vast array of variables in design and wind seas conditions from there much better than either rating system does independantly as per currently used.
By using both systems they could both be simplified greatly and compliment or correct one another and would certainly become more accurate if adopted internationally providing more verification of the yardstick aspects in larger numbers ,--along with some added thoughts in ranking racing sailors in basic skill levels to correct this aspect further .
The simplification of the design measurement portion would be from the reliance on the yardstick aspect to compensate lesser design features that historically make design measurement rating systems counter productive by penalizing excellent design and thus to design progress and creative development. A design measurement rating system only in an effort to compensate all design variables makes them too complex to comprehend ,-the end result being a complex partial effort at total design annalysis subject to differences of opinion in design values in the equation.
There are numerous other reasons to develop a combination rating system that become clearer as it is thought through.

Outlined ---the combination rating system would not use the rated formula and proceedures in determining weight length or sail area ,-a simple direct boat weight -o a length -and sail area used ,-in a base equation ,
-Sounds like your working through proven proportional factors added for spin -non spin -jib -main only sail plans and single or 2 crew variables ,--this would keep it simple -and again the yardstick added to this as compensation for lesser design variables at a correcting percentage should be more verifiable over time with larger input sources internationally and a ranking system for racing sailors to compensate skill level unknown to some extent of the yardstick aspect .
The model end power formula of Texel similarly used but now in very simple form easily understood and calculated .
Think the end number factor in the power formula could be scaled to corespond to the 5 windspeeds currently used in Pn rating . Porportional aspects as to the division of length weight and sail area in design are established though some would state sail area is over emphasized in the equation . Again the correcting factor of the current yardstick system applied as a percentage factor should compliment the design measurement basis ,-there would be no need for the one size fits all approach modification factors currently used in Pn being replaced by actual sail area L B W measurement base numbers .

This basic approach in outline may be worth considering as better alternative ,--hope this is constructive and helpfull ,and also inspires others to think though an improved rating system that may be adopted internationally .

Happy Holidays
Carl