Comment directed @ readers:
Thickness affects stiffness (stiffness is related to the cube of thickness). Material properties affect stiffness. Flex is affected by length too.
3-4 Gs can be exerted on a surfboard during a hard bottom turn. Assuming a surfer weighs 160 lb, what is the measured distance of static deflection for the nose and tail tips relative to the midpoint for a 480-640 pound weight place centrally on a surfboard’s deck distributed over an 18" distance? Simple data to collect as a relative reference point for discussion and comparisons of surfboard flex. Obviously static flex is not the same as dynamic flex, but some empirical data are better than no data – data are not affected by beliefs.
I defer to George Gall’s (PlusOneShaper) – engineer and mathematician surfboard builder – discussion about flex at the following links (last half of first link and first half of the second link):
http://www.swaylocks.com/comment/497273#comment-497273
http://www.swaylocks.com/comment/497387#comment-497387