: Paul,

: The question is how much strength do you get with no cross grain
: reinforcement.

How strong does it ned to be? the water pressure compressing the wood is under 1/2 p.s.i. A sheet of paper can hold withstand a dozen times that. Cardboard and thin wood are hundreds of times more resistant to pressure.

: Plywood has a crossgrain ply, Tom's 2 plys in the same direction
: does not.

True, but he is overlapping two strips. Each strip has it's own grain pattern, and the combination seems to let one layer of strips reinforce the adjoining layer is made from veneers. Some are cut like thin boards. Others are cut in a rotary manner, and the resulting grain pattern is nothing like what you might see in a cut board.

Use enough glue and you can make a "board" from shredded wood fibers or even sawdust. Not sure what grain would have to do with something like that--but particle board and OSB, in the proper thicknesses, are structurally sound. Epoxy over a strip turns it into a combination of wood and plastic. The resin which soaks into the wood greatly strengthens it. To some extent varnish and polyurethane coatings also add a small amount of structural change to the wood.

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

"added thickness in certain places" might be more accurate.

With thin strips the direction of the grain has more to do with its ability to bend, or resist bending. A bow (archery) has the grain running from end to end and when you pull back the string it flexes, first absorbing great pressure in compression (on the inside of the bow) and tension on the outside of the bow, then releasing that when the bow string is released. In a boat the load is mostly carried by the gunwales, and the ribs transmit this load along the sides and up to the gunwales. They could do this with any orientation of the grain. One way might be slightly better than another, but the size of ribs can be very slight, and they will still do their job. Check out the minimal framing used by Platt Monfort's Geodesic aerolite boats (www.gaboats.com)

: 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.

The people at Pocock might be surprised to find that they are antiques: The company has been around over a century (1911). check out their site at www.pocock.com. The Wooden Boat Foundation in Port Townsend WA inherited the mold for forming the Pocock shell about 2005. I saw it in 2006 when they were setting it up. Since then they have produced a few new 'antiques' and sold them to subscribers as fundraisers. I just found a recent webpage about these boats at: http://www.pocockclassic.com/ or try http://pocockclassic.com/Pocockbrochure.pdf which shows the old mold.

There is a central frame of sugar pine which serves as thwarts and replaces ribs. As i recall, the crossection on these pieces is only 1/4 " to 3/8". More like toothpicks than ribs! The deck is of a thin fabric. Fabric and hull are varnished. no epoxy. No fiberglass. Just strong wood.

: 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.

You would get a lot of strength by laying the two layers at 45 degrees to the centerline. They would cross each other at 90 degrees. Going from one gunwale to the other you could probably fit the strips fairly quickly. Bead and cove just might be practical here. Quickly applied square -edged strips which don't quite fit together might leave big gaps with a single layer of strips, but when you put on a second layer--even if the seams are not very tight, the only areas which might leak are the small points where neither layer covers. Those small points will be filled by your glue or epoxy, or sawdust and varnish as you fair and finish the hull.

Starting at the keel and working to the gunwale, with each side of the boat stripped in a herringbone pattern gives a central seam which can be backed by an internal keel or keelson. The second layer again starts at the keel, but goes 45 degrees in the other direction. The boat has an intersting diagonal pattern. The deck can be stripped herrigbone to match, or by laying straight strips.

The idea of crosswise weaving of fibers, split wood, or wide plant leaves goes back to antiquity. The earliest common reference to this is the biblical reference to Moses being placed in a cradle-sized boat. Same pattern, but we are not weaving the wood strips (they are too thick to bend easily).despite all the seams and joints, woven baskets can be made which will hold water--the fibers swell to seal the junctions.

Hope this helps

PGJ