This is easy to answer.
For the sake of the argument I shall not press home the point that the F12 is not specically for kids, but more for any person in the range 40-65 kg. This will also include teenagers and small adults.
But back to just youths.
One-design boats simply aren't fair to youths.
First of all how One-Design are youths anyway ?
If they aren't then why should the boats be ?
Allowing some freedom in adjusting the stiffness of the rig and sail cut will allow some of the inequalities between kids to be corrected. It has been shown many times that the classes with the highest sensitivity the crew weights are the OD classes.
It is in my personal opinion a downright myth that differences in material (under formula rules) are significant when compared to differences in crew skill. It is incredibally easy to show how different designs result in maybe 1%-3% difference in performance while differences in crew skill will easily result in up to 30% difference in performance. And we should not forget that aging boats will sails older then 2 years will also be about 1%-3% slower around the course. In short, if your kids needs to sqeeze out those last 1%-3% of performance then he needs to by new gear every two years anyway, irrespectably whether he is sailing in a formula class or OD class. If that is the case why then accept the downsides of OD classes which are :
-1- expensive replacement parts, sometimes even of mediocre quality.
-2- not allowed to source your own (local) suppliers of parts or make them yourself.
-3- no continued (but slowed down) development, meaning the class will grow outdated in 10 to 15 years time.
-4- less builder support as only one builders needs to do everything. Why do formula classes come up so strong ? Because several builders and suppliers are pushing it in one coordinated effort.
-5- A nightmere scenario when having to check boats for compliance at events. EVERYTHING needs to be checked.
-6- Either the design is very good but impossible to homebuild or it can be easily homebuild but everybody is sailing bathtubs.
-7- OD doesn't allow quick and dirty homebuilds to allow easy and inexpensive acces to sailing.
-8- Problems when US builders are not using the SI unit system. Is 1/16 steel wires the same as 3 mm steel wire ? Ask the Hobie 16's how such a thing lead to a right protest frenzy at one event. At one event in the 80's the crews were checking eachother boats with caliphers trying to spot US stays and protest the owner out of competition. That will be a good behaviour for your kid to learn.
And since parents will be building the boats (theoretically), it would just become an adult competition to see who can build the fastest boat.
That may be true to some small extend, but how is this different from your kid chosing the right tennis racket for himself or the right mountain bike or even the right track shoes or skis/snowboards?
Why do we in sailing land think that chosing the right gear for your body setup and preference shouldn't be a normal part of competing ? In by far most sports it is. A top level tennis player will replace his racket 4 times during a game ! If you choose the wrong mountain bike gear setup for the course then you have a problem.
How many one-design cycling events do we have ? If you go and play tennis, do you make it a point to play with the same racket ?
As such having to choose and optimize your gear to suit your body and way of sailing is actually sending the right message to your kids.
And it does benefit youth sailing by being.
-2- better available
-3- better developped
-4- better promoted by a bunch of builders (future)
But I think that this has been discussed many times over Mary. You do seem to ask this question a few times a year.
Doesn't the wave class allow different mainsails ?