:. . . But... If you're going through all that
: work why not just build it "traditionally" since your
: time/weight savings just evaporated applying the interior glass/epoxy...

Not completely.

Ideally you would use the same amount of resin as glass (by weight). If you use thick layer of glass (say 6 ounce glass) on the inside, your weight gain is 12 ounces per square yard. If you use a thin layer of glass (say, 2 ounce) then your weight gain is 1/3rd, or 4 ounces.

With glass of any thickness, as you apply the resin the glass serves as a depth gauge for controlling the thickness of the resin you are applying. If the top of the glass is covered, then you have on a layer of resin which is at least as thick as the glass itself. If you just want to ensure that you have a solid coat of resin to keep the wood protected from water damage, then any thickness of glass will do the trick--even superlight glass in the 1/2 ounce or 3/4 ounce ranges.

Obviously real thin glass is not going to be as strong as thicker glass layers. It will just weigh less. The actual weight gain or savings is going to depend on the thickness of the glass you use and the amount of resin, when compared with the weight of the ribs you leave inside.

Uncoated cedar is pretty resistant to rot and decay. Covered with even a single coat of paint or varnish willmake it last a bit longer. If you are looking for lightweight and willing to trade off for a shorter life span for the boat, you don't really need to do anything to treat the wood inside. Slosh some borax solution around to saturate the wood with a nearly weight free material to delay mold and rot, then let it get wet. After use, drain it and let it dry out.

The question keeps coming up about attaching the deck to the hull. In any situation where I would be worried about water buildup, I'd either have a large hatch, or make the deck removable. If the hatch is large enough you can reach through to do any glass tape you might need for reinforcing the hull/deck seam. If you are going to use a wood strip atached to the top strip of the hull, as a backer to hold the bottom strip of the deck in alignment, then why not use screws to hold the halves together. You can make a "gasket" of silicone-based caulking compound. Squeeze a bead on the backer strip and when you tighten the screws they'll pull the deck and hull together and squeeze that gasket firmly.

Or, make your deck out of cloth. Racing shells used to do this--and some probably still do. You can use a very light nylon or dacron coated with urethane or polyurethane. If you are leaving the forms inside they will serve like thwarts to keep the sidewalls braced and stiff. Or, you can replace them with thwarts. If you space them close together they can be made from very thin, and very lightweight stock.

Look at Platt Monfort's Geodesic Airolite (www.gaboats.com) hulls and imagine that you are just doing that for the deck. You can attach the cloth as he does, by ironing on a heat activated adhesive.

You can make a lot of compromises to save weight. But a lot of those compromises will cut the life and durability of yor boat.

If you want to reduce the overall weight, sometimes it makes more sense to cut the weight of the paddler instead of the weight of the boat.

Just a few thoughts.

PGJ