I did manage to find a design for a good nesting dinghy but its still
75-85 lbs. Then I looked at that Airolite boat site about
ultralightweight boats made from dacron skins on a lightweight frame.
His designs, especially his 8' dinghy are closer to what I have been
imagining. He also discusses Tyvek sails and putting the two together
is sorta fleshing out an idea.

So, essentially, the dinghy problem for sailboat cruisers is that many
of us have mid-sized sail boats (mine is 28') with not enough room to
carry a dinghy of any size on deck. Even when we do carry such a
dinghy on deck (mine is a Nautilus 8), the thing is so heavy, we have
to use the jib halyard as a hoist to get it in and out of the water.
Even then, it can be exhausting to launch or retrieve. Even then, it
will not really carry my wife, myself and two kids and I have 3 kids.
It does row well though. An inflatable could stow well but inflation
is a problem taking at least 20 minutes and they do not row at all
thus requiring a motor. A Porta-Bote is an expensive option but even
they seem difficult to stow being at least 10' long and from what ppl
say take a lot of time to assemble. Nesting dinghies seem to be an
option lessening the stowage problem but I can just imagine trying to
assemble it on a small foredeck and can imagine difficulties
(dis)assembly on the water even in small chop. 75-85 lbs is still a
lot of weight to lift even if its in two parts. The Airolite dinghy
at 28 lbs looks great but I think I really need a 9 footer and maybe
10. Even the 8 footer might have stowage problems (although less than
the existing dinghy).

So.........Instead of the Airolite concept where the geodesic-like
structure where the frame carries the load with the dacron simply
covering it, I envision a sort of tensile structure where the skin
hold the frame in tension like an inverted free standing tent with
internal poles. Flexible fibreglass batten like poles would run
lengthwise through tubes in the skin from a common point at the bow to
the edge of a stiff transom. Widthwise battens would be inserted
through loops and joined to the battens at the edges to form the hull
shape. Lightweight seats would help hold the shape. I am not yet
sure of how to fasten the widthwise battens to the lengthwise ones but
various things come to mind such as the fasteners used to secure
canvas to things. Ont he outside of the skin would be a keel of
lightweight fairly stiff closed cell foam (I have various types of
this stuff at work so have been looking at it).
Although Tyvek is permeable, I may experiment with it because of its
tear resistance and low cost. I am certain that some type of similar
material is available that is waterproof.
Any thoughts on this?