: I am planning to build a tortured plywood or compound bend boat and I am
: wondering why there is so little(almost none) information on this form.

In two words, the term that answers most of the questions is: "developable surface". A flat sheet of paper, wood, steel, or aluminum can be bent into many simple curves, and also many complex curves. If you have a shape which can be made without stretching the material too much it is caled a developable surface. Unfortunately not a lot of these shapes have good potential as efficient hull shapes.

Even those compound shapes which DO have good potential for hulls frequently can not be made with a single layer of plywood, as the material must be so thick (for overall strength) that it can't be bent sufficiently without tearing or delaminating.

Interestingly, some of the early boats in North America were made by placing compound curves onto a flat working material. The result was the birchbark canoe. Where the bark material did not bend enough to fit the proper lines of a boat it could be slit, the excess reoved, and the gap sewn shut with roots. Seams and patches were sealed with a pitch made from thickend tree sap.

In some cases the very nature of how plywood is constructed limits the process. Plywood is typically constructed of an odd number of layers of veneer, with the two face surfaces having the grain running in the same direction ( usually in line with the length of the original plywood panel). The interior plies, which make up the core of the plywood sheet, have the grain rotated at 90 degrees on alternate layers. The idea here is to create a material that is resistant to bending. That's probably why the plywood must be "tortured" and not just bent.
With some tortured plywood designs a few slits are made in the plywood panels, like darts are made in clothes, to adjust the curvature. These are eventually spread or drawn together and sealed with (typically) fiberglass cloth and epoxy resin.

Clarkcraft (www.clarkcraft.com) has plans (BK59) for a "plywood" boat where you avoid this inherent stiffness problem by making your own molded "plywood" thru the process of laminating 3 layers of flexible sheets of veneer over a mold. it doesn't exactly qualify as a tortured plywood boat, but it does give more flexibility to the design process. there is a picture of this boat at the bottom of this note. In their online catalog they give the description a headline suggesting that the boat is canvas covered, but the further description makes no mention of canvas. Just veneer.

There are some specialty plywoods which are specially made for bending. These are usually rather expensive, and used for building columns, rounded ends to kitchen cabinets, and large diameter plywood tubes. For compound curve they may, or may not, be an advantage. It depends on how much you have to stress the wood against its natural flexibility.

In a design where the plywood must be bent an extreme amount, sometimes to the point of crushing the fibers in the middle core layer(s), a particular brand or specification of plywood may be required, and substitutes may not work at all. Sometimes that means that the home builder in one part of the world may have access to materials, and a person elsewhere will have to pay huge shipping costs for materials which are not inexpensive on their own.

A few designers like to work with these limitations. Some have come up with some great ideas. And some other ideas are dogs.

But, if you get past those problems -- and many people have -- it can be a quick job to make a few slices in a panel and bend it into a boat.

: The boat is for my young children and the water we will be on will be
: lakes and rivers. The material I have read indicates that they are light,
: easy (tricky) to build, inexpensive with good stability. So, why don't
: more people build them? Any comment would be helpful.

Waht design were you thinking of. The one I've read most about is the Yare, a design written about in Chris Kulczycki's book "The Kayak Shop". It appears simple and fast to build. Actualy, it is on my list of boats to build, and I bought some 1/8 inch Meranti plywood with the intention of trying it, but I have put the project on hold. From other comments on this board it appears that I might weigh too much for this boat. Either I lose weight, or build this for a friend. Also, a few people who had built this design did not like the stability, or the tracking. As a river or small lake craft for people smaller than me it might be ideal.

hope this helps

PGJ