Paul,

The question is how much strength do you get with no cross grain reinforcement.
Plywood has a crossgrain ply, Tom's 2 plys in the same direction does not.

Most of your illustrations show the need for some cross grain.

It has always been clear that boats can be lightly built and survive in "special circumstances". I looked at an antique rowing shell (Pocock) which was 5/32" cedar, one layer, no ribs, no glass and it was 50 years old. Of course the lady who owned it would not let me help pull the boat out of the shed, for fear I would cause her to bump it and crack it.

There really was no need to ask the question, except I wanted to hear Tom Yost's answer. It is interesting to see that in lake useage the boat has had no problems - at least I assume that.
If I were to do one with out glass I would lay the two layers at slightly different angles, which would substantially improve the "cross grain" strength.

: Marc, you would not need glass with a boat built from 3mm, 4mm or
: 6mm plywood--all of which would be thinner than Tom's 1/4 inch
: lamination. In effect, Tom is making his own plywood, bent to
: the right shape as it is applied to the forms, with just 2 plies
: and a really strong (epoxy) glue. He could have used thinner
: stock! If he went with three plies of 1/16th inch his hull wouid
: be 3/16 thick--about 4.5 mm. Working with material that thin he
: could do all his trimming with a sharp knife and put away the
: power tools, too!

: If you look at the cover of Canoecraft by Ted Moores you'll see two
: canoes of similar size and design, which are about 75 years
: apart in age. The older one has wood ribs on the inside, the
: newer one is sheathed in fiberglass cloth and epoxy resin. The
: fiberglass replaces two functions of the internal ribs. One is
: providing a mounting surface for each of the strips. The other
: is to give some strength in a direction opposite to the way the
: wood grain runs in the strips.

: Look inside a wood/canvas canoe and you'll find crosswise ribs.
: That design idea came to us from the builders of birchbark
: canoes. When big birch trees got scarce we kept the frames and
: covered them with other materials:thin wood slats, canvas,
: paper, fiberglass cloth, polyester, and so on. The strength
: comes from the shape and bracing, not from the actual thickness
: of the skin.

: crisscrossing the plies of the veneer or strips used for the layers
: supplies the necessary bracing to replace ribs and/or fiberglass
: on the inside of the boat. Glass on the outside is mostly for
: scratch and dent protection, although it does a nice job of
: holding the strips in place, too.

: Just a thought

: PGJ