Hi Jeff, 

i had not been thinking about it but had been researching paddleboards recently for new project with my daughter.

first, interestingly enough, somebody has tried it.  see the link to the kickstarter campaign below.  on the face of it, looks reasonable.

https://www.kickstarter.com/projects/artechllc/easy-eddy-three-piece-modular-paddle-board

that said, i have thought of elements of this having been involved with this recent paddleboard project and also having been involved in homebuilt aircraft....where being able to remove the wings for storage...is a fairly common problem and feature....and wings are a bit like a paddle board (they need to be stiff) and they are relatively slim (not thick) and you don't want them coming apart.

if it was me, i might experiment with removable carbon fibre tubes acting as spars to hold it all together but a tight fitting tube-within a tube so it can be assembled/disassembed and to carry most of the loads.    as a high-level concept,  i would have three sections of board (5 foot middle and 4.5 foot ends) and 4 four foot tubes tieing it all togther that would slide into/be secured into close fitting tubes in the center section, for and aft section.   there would need to be some kind of clip in the top and bottom skins (similar to the kick-starter design) to keep everything tight.

anyway, i have little doubt you could do it with the right board design (not so much rocker), the willingness to take a little weight penalty, and some patience to sort it all out.

h

   Pope used a similar system of tube and clip on my bisect surfboard and a SUP they sold called the trisect. Reviews I read about them identifies flex issues. My bisect failed me while surfing head high Hawaiian in Kauai. The shearbolt clips broke under the stress of an epic wipeout. Tough to replace and a bit impractical. I do have 2 bisect tubes to try it out, but using a different hardware. As for where the sections should go, looking to sister a design support location. Makes using fullsize templates practical. As you suggest, weight does become a restraint. Not sure about rocker issues. My bisect has a fair amount of rocker. Would be harder to build with rocker and seems counter intuitive for greater glide.