Because of resistance to puncture, isotropic properties and stiffness.
Foam sandwich doesn't work for small boats. To get sufficient resistance to
puncture, the skins must have a minimum thickness. For mechanical reasons,
we should use tri or quadriaxial while with plywood only biaxial is needed.
A sandwich panel made that way would be heavier than a plywood-epoxy-glass
sandwich.
Once you get around 27', foam sandwich becomes a valid choice. With
vacuum-bagging and aramids, we could build smaller units, donw to 20' but
the cost would be very high.

PS: about poplar, there are no fasteners in our boats . . .
--
Jacques
http://www.bateau.com

"Backyard Renegade" wrote in message

Why not make the panels of foam and skins, like vacume bagging?
Scotty