[JonEisberg]

Have a look at the designs from B&B, Graham has drawn some very sweet boats… I built a nesting Spindrift, really nice little boat that rows beautifully. If you built one from a material called Coosa, it could come in at a fairly light weight. I've never used that material, but have heard great things about it…

spindrift

Now, if you want to go ultra-light, have a look at Platt Monfort's boats, they're very cool… Whether they would stand up to the rigors of use as a yacht tender, of course, is another matter…

Geodesic AiroLITE Boats - ultra lightweight SOF canoes and boats; plans, projects and tutorials

 

[JonEisberg]

I would like a lapstrake dinghy, very light, collapsible (see porta-bote) capable of rowing, motor and sailing, and carry 3 people and be around 8 ft in length. And not cost an arm and leg.

Wow, good luck with that one... (grin)

Something like CLC's Eastport Pram in a nesting version is probably as close as you're gonna get... I have difficulty picturing how anyone would configure a "collapsible" lapstrake design...

http://www.clcboats.com/shop/boats/wooden-sailboat-kits/eastport-nesting-dinghy.html