My most recent build, boat no. 11 for me, is an Outer Island (my second OI). At 18' x 21", weight came in at 30.5 lbs, not bad. Layup is 4 oz s-glass inside and out on the hull, 4 oz s-glass in the inside of the deck and 3.25 oz satin weave on the exterior of the deck, hull and deck joined with 4 oz s-glass "tape" I cut myself on the bias. I added a 4 oz s-glass piece over and under where I sit in the hull, and another bit around the the coaming underside.

The trick to keeping things light is to watch each and every gram that goes into the project, and reject all possible. I would never use hardwoods on a boat (of mine), for instance, since I believe there are lighter alternatives.

I made my forward bulkhead from a piece of fiberglass matting "molded" on a piece of 1/2" glass I keep around for making flat things, and cut to shape, see picture. It weighs considerably less than the wood version.

The boat is going into its 3rd season of hard use now, and OMG I LOVE IT!!

http://ngc704.home.comcast.net/~ngc704/NewOI/Page_8.htm