Plywood Kit Designers

If you have a class that already has compound curves available via the composite route it still does not matter how tight you then set the measurement rules .. whatever the rules or wording you simply cannot make ply bend to match the compound curves that are very straightforward in an optimised FRP composite.

'Modern' phantoms will always be faster as they are simply better shaped than can ever be achieved via bending and twisting 8x4 ply sheets.  You cannot copy the compound curved shaping.   Look at all the other traditional, originally plywood and chine, classes that made the transition down the years (with the possibly partial exception of the OK granted) - the ply build has died on its knees as a competitive or worthwhile build route. 

With regards to why a wooden OK can still be competitive and a wooden Phantom not, I would suggest that a wooden OK, given the size, mass and panel sizes, can be made "very" stiff.  Probably stiff enough, if not as stiff as a composite one.  A wooden Phantom at minimum allowed mass has large panels with minimal support, so it is easy to see why it cannot be anywhere near as stiff as a well-engineered epoxy sandwich boat. Having said that, it is not immediately obvious why a less stiff boat should necessarily be that much slower.  It is not as if you are trying to control jib luff sag with rig tension.

Jim it is indeed the case that wood boats are as fast as foam sandwich ones in the OK. It is probably for all the reasons above but it is encouraging to see that this is a possible route again now we are all supposed to be more careful about sustainability etc. The table below is from the last Worlds in early 2019 taken from (https://www.yachtsandyachting.com/news/215612/Individualistic-choice-of-OK-Dinghy-Equipment).  

The article also sys that only four of the top ten were production boats, the rest being either home built, or built using Dan Leech's CNC kitset plans by professional builders and the third placed boat in Auckland was 35-years old Icebreaker.