Arguably both the Texel and ISAF systems use of only one rating number for accurately predicting performance over the full spectrum of wind strengths from 3 knots to 25 knots is a big ask. This is especially problematic when looking at spinnakers.
On the other hand the average DPN of yardstick in no better in this respect and many Race Committees dislike the 5 individual ratings that some yardsticks use. It requires much more effort from their part to measure the right wind speed and it makes rating calculations more cumbersome. Also in principle the ratio between different ratings numbers is surprisingly constant while the individual numbers vary. This is hardly effective. Alot of trouble for not much gain. Add to this that you need a minimal amount of data for each group to make an accurate regression and you'll get the picture of the work involved. It in no wonder why many RC just use the default numbers and be done with it.
The proposel to solve this deadlock is to have two rating numbers instead of 1 or 5 or more. 2 allows more freedom to improve accurate prediction for arguable very different conditions (trapezing and non-trapezing) and is alot simpler to use and maintain than 5 numbers.
Arguably designs will really only differ in performance on the threshold of going from non-trapezing conditions to trapezing conditions. It is the transition from always sailing under maximum achievable power to sailing under maximal controllable power. As a result there is not much to be gained to sub devide these two very different regions in more sub groups. So lets take the transition that is really important and forget about the rest for sake of ease of usage.
Also it is alot easier for a RC to determine which rating they should use just by looking at how many of the boats are trapezing. If this ratio is less than halve, you use the low windspeed rating, if it is more than halve you use the high wind rating.
By dividing the performance predictions in two groups of numbers we can also compensated FAR more easily for the swing in performance experience by singlehanders and spi boats when the transitions from sailing in light winds to heavy winds.
For example : the singlehanders and spi boats will get relatively faster ratings in the light winds group when compared to their ratings in the high wind groups. We can split any offsets that may exist in halve using this setup without really increasing complexity of the system used.
There is also a lot less potential for conflict. Either halve the fleet was trapezing on the upwind or they weren't.
For further details I refer to the posts about the individual mods.
Wouter
