I spent a lot of time researching this topic some years ago. I think that there are some big misunderstandings expressed in the discussion. My research looked at boats that were originally constructed in plank on frame wooden construction and which were converted to glass. I looked at a number of early boats like the Lightning class, Folkboat, H-28, and Rhodes Bounty.
In a general sense, the hulls on the wooden plank on frame boats were lighter and stiffer than the glass boats. In other words, the wooden boats flexed a lot less than the glass boats. In the case of the keel boats, this lighter weight meant that the wooden boats generally had more ballast and so had greater stability and in some cases carried more sail area than the glass boats (H-28 being a good example of that).
The reason that early fiberglass boat hulls were so heavy was that it was very hard to replicate the stiffness of wood without going to very thick fiberglass and since Fiberglass was so dense it quickly outweighed its wooden sisters.
This situation changed when designers began adding internal framing and then coring to fiberglass boats (late 1970's and early 1980's) . A properly framed glass boat can have a lighter, stronger hull than a plank on frame wooden boat.
Cold molding is another animal all together from plank on frame. Its weight is very dependent on the species of wood used, and the care in lay-up but in a general sense a cold-molded hull is lighter than a plank-on-frame wood hull but a bit heavier than a framed glass boat of similar strength and stiffness.
Generally speaking a carefully constructed cold molded wood boat will be less maintanence than a fiberglass hull and will be a lot more durable. I base this on an industry study comparing the life cost of various boat building materials that was done some years back.
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Curmudgeon at Large- and rhinestone in the rough, sailing my Farr 11.6 on the Chesapeake Bay and part-time purveyor of marine supplies