> hello nick (& the rest),

> I read your response here & I'm surprised !

> I respect your opinion. I believe you know about kayak building/ designing
> much more than I do, but something here isn't clear to me.

> just like you said, the construction method in discussion works very well
> with the design method you described, & that's probably the way the
> inuits & aleuts did it.

> but aren't we trying to create a kayak with certain behavior
> charachteristics ? a certain amout of initial/secondary stability ? a
> certain amount of bow/stern floation ? prismatic coefficient ? etc'.
> aren't we looking for a design method that will give us a better
> prediction of the behavior of the future kayak, than the prediction we get
> with the inuit/aleut method ?

> my theory says: make a kayak that will give you the behavior/responses
> you're looking for. not the look. worry about the look when you buy a car.

> what will he do if he puts his new kayak on the water for the first time,
> paddle it for 20 minutes & say: "this thing sucks ! my plastic is
> much better ! " or should I ask, how can he refrain from getting into
> such situation ?

> am I the only one ?

> is my theory wrong ? (no, I don't intend to change it)

Well, parts of your theory could be improved on -- and I think you point that out, yourself.

As you say, the function is most important. Behavior/responsiveness, stability, speed, displacement, and capacity are important criteria to consider in a design. But, a person with any knowledge of these items already has some ideas about what they want.

It is merely necessary to translate these ideas into a solid form and try them out -- to confirm or disprove the theory used in the design. This type of design method is called trial and error. If the errors are easy (or cheap) to overcome then this could be a very efficient way to design. something.

Nick proposes a time honored way of doing a full-size model. With skin on frame kayaks this is the quick and dirty way of doing things. The boat skeletons (frames) are cheap and the lines of the boat can be quickly assembled and measured. Such items as prismatic coeficient can be calculated from numbers derived from accurate measurement of the actual boat as it is assembled. With a plane and a saw you can alter the shape quickly and cheaply.

Birchbark canoes were built in a similar fashion to Nick's suggestion. The gunwales were constructed first, then the birchbark was laced on. After that the ribs were inserted. Rocker was built in by varying the depth the ribs were inserted. Wetted surface area tok care of itself. since the bark was basically a flat material. any hull shape you could force it into would still be (from the point of views of a geometry student) a flat surface -- folded, but none the less flat. If you don't stretch the material,(and birchbark is hard to stretch) it is forced to take a shape that gives nearly the minimum wetted surface area. You can tinker with the shape to improve things as you build.

One area of the mathematical field of topology, which fascinated me as a kid, dealt with using soap bubble liquid on a frame model to find the minimum covering, and the point os intersection. Dip your model in the soap solution and remove it. The surface tension of the soap solution caused the soap film to contract to the smallest possible size. With a fabric skin over wood frames, the smallest area will be found when you carefully pull out the slack as you staple it on. Is this good design, or good luck? I'm not sure, but it worked for centuries before computers, and I hate to knock something that venerable.

Ancient peoples proably thought of their boats as utilitarian craft, not race boats. Their design criteria were probably suitable for the construction techniques of their day. Even so, a discerning eye and a clear mind can asist someone looking to buy a good boat --

Just some thought on the value of older methods in a newer environmenr.

Paul G. Jacobson