Take a look at this link: some good tips by Ted Henry:
http://metakrome.com/kayak/light.html

In a nutshell: use as little epoxy as possible, which may be accomplished by treating it as if it cost $100000/lbs.
If you don't bang the boat on the rocks you can use 4oz glass. If you use 4oz S glass you'll end up with boat not only lighter but much stronger than standard 6oz glass. Easy on hardware - use mostly foam and wood, not metal and plastic.

: Hi, I'm looking for various suggestions on building light/superlight s&g
: kayaks. If we leave the design aside- the use will be jetty stair launched
: and paddled in an estuary and an open harbour/coast with sea swell but no
: breaking waves.

: what would you usually build and what would be your lightest version?

: I also read of a thin frame with open bulkheads that thin ply was then added
: to is this light?

: regards ewan.

: also i did try a search but you get walloped with hits.