I stumbled on this thread and initially thought it was just a p**s taking exercise. After reading it carefully and a few other threads on this part of the forum it seems there are some people who actually believe there are no speed advantages for stiffer OTB cat platforms.
Those with short attention spans please continue Twittering - for the rest grab a cuppa and I'll offer my views.
I come from a background of thirty years sailing OTB cats at regional, national and world level. I've built and refurbished both timber and foam sandwich boats.
I note the undercurrent of personalities here and provide the disclaimer that I don't know Macca but have sailed against his Super Taipan with Griffo as skipper.
I'll ignore the red herrings in comparisons with gliders and bicycles. The references to mast stiffness are also irrelevant as masts should be matched in bend characteristics, to sail shape, boat type, sailcloth, crew weight, usual sea conditions etc. That is where the beauty of carbon masts comes in. They can be laminated to suit the exact needs.
Platform stiffness though I believe has a significant impact on boatspeed, particularly on acceleration and through choppy water. Going back to basics, the platform is the structure which transmits the power of the rig to the lateral resistance provided by the hull and the foils in the water. Any bending or twisting in the platform absorbs energy which would have been applied to forward motion by a stiffer platform. The class I know best is A Class cats where stiff platforms are the holy grail. The sloppier platforms simply don't cut it - the stiffer platform just inches forward in each gust as the acceleration is more efficiently applied.The timber boats we built in the eighties just could not be built as stiff as foam boats and the last timber A to win a worlds was Billy Anderson in 1980. I agree that stiffening one area sometimes leads to showing up a weakness somewhere else. Simple - beef up the weak area - thats development.
As far as Tornados are concerned, if a cedar T is so stiff where are they over the last twenty years in the Olympics and Worlds. Haven't seen them winning there.
I agree with Aido about H16's. In the eighties the Metcalfe boys pretty much dominated World titles in 14's, 16's and 18's. They had a standard procedure with the supplied boats. It revolved around making the boats as stiff as possible in the short time available. Even to this day the local and very experienced Hobie dealer sets each new 16 up to improve stiffness over the standard factory delivery.
The recent AC saw Alinghi use significant structural bracing to get platform stiffness. Oracle mainly kept it's centre hull as it gradually morphed in to a cat so that it was stiff enough to limit forestay sag
It is true that building stiffer platforms has diminishing returns. However in a restircted development class you would expect people to keep trying for that extra bit. That's the beauty of formula development. Look at the F18's. Would you rather sail the latest C2, Infusion or Wildcat as opposed to the first Tiger with pinhead sail and fat boards and not so stiff platform.
Now, cuppa finished and off to the shed to do the winter maintenance on a bloody timber boat.

Cheers