> Didn't the book that taught you how to build boats give scaling rules?

hmmm, this isn't rocket science although one can appreciate the formula for acceleration of a falling apple,,,or one can catch the apple toss it to a friend or eat it. Newton probably did both. The books are a fine way to learn something absent of learning from a person. The formulas are a useful tool to see things that experience has yet to teach. But George this isn't rocket science and if somebody is building a kayak to be the lightest that can be made from a particular set of materials then that person is providing a rich source of material for seeing where and how things break. In other words real light stuff breaks more than stuff that is built with other priorities than ultimate light weight. At some point a person has to ask: to what purpose?