On Mon, 29 Jun 2009 13:50:56 -0500, Vic Smith
wrote:

I was thinking along the lines of styrofoam-like weight.
Hardened on the outside with something light, and maybe
internally stiffened with something light.

Yes, like a SeaRay !

(I can talk like that since I own one)

It's important to remember that "ride quality" and "sea worthiness"
are only loosely related. You can in fact take a boat with a hard
ride and make it better by adding weight. At the same time however,
freeboard is lowered which makes it inherently less seaworthy, and
possibly less stable depending on where and how the weight was added.
Also, fuel consumption will increase and speed will decrease.

There's just no free lunch here.