Good post P18 (and Bill)
It has been (is) a very interesting thread.
Just to clear 2 things up
I never said anybody wasn`t a "Windsurfer" (or sailboarder)Think we are all both.
Just think "sailboarding or lightwindsailing or Div2 or Div1 or Displacment sailing" (whatever you want to call it.) should have maintained its own idenity. (ie to try and foster some security in purchasing race oriented (All wind) kit.Everybody (mags;manufacturers forgot about highly efficient low wind diplacment kit.Serenity is #B first forray into efficent non-planing hulls.(After 20years???)
You are correct re- upthrust exceeding weight.(Its when control problems occur;and why thin tails /cut outs aid high speed control) Should have said equal.(ie board fully planing when upthrust equals weight)
Above certain speeds buoyancy (on flat water) has very little effect.(apart from negative ones) Modern Wakeboards are bouyancy neutral.(ie no bouyancy;no float;they weigh same as water but the still plane fine). A neutal buoyancy (sail ???)board would work above 3mph ????(in sufficient wind)
Have a look at older thread about planing theory. (momentum exchange)
Putting it simply most "models" of planing are under attack/review.Many (Scientists/Engineers) arguing simple momentum exchange but its OT.