My Minicup was made from 1/4 inch marine ply, and I used the comman
bath scales with a scary rig arrangement to weigh it and the bare hull
--no rudder,no centre-board come up to some 170lbs. Not easy to
cartop.

In reply to the question What is "skin on frame". -- you build a
frame of wood or other material to conform to your hull shape and then
cover it with a waterproof "skin" which will enable the frame to
float. Just Google it. The 16 foot kayak I built weighs under 30 lbs.
For those interested see www.yostwerks.com.

Re the SOF-Mcup design, I wonder if I should add a wee bit of rocker
to keep the transom end out of the water. Will try to input into
Carlsons Hulls, if some one has done it, would appreciate receiving
the file.

Cheers