: I'm building a Tom Yost "Sea Flea" in the 12 ft version.
: I can find the spacing of the cross sections for both versions on Tom Yosts
: website, but I don't know how long the bow and the stern extend past the
: first and the last cross section. . .

Take another look at the illustrations on Tom's website. When the tubes are bent around the forms they acquire a natural curve. If you leave enough overhanging tube, the tubes from the left side intersect those from the right. Mark where they cross and you'll know where the ends go.

As I recall Tom has a good picture of the tubes overlapping each other, but perhaps the caption didn't make sense at first reading.

: . . . Is it right to have the stern and bow
: extend for the same length from their respective cross section?

If the molds, ribs or forms are symmetrical and spaced the same distance from the center of the boat, then the boat will also be symmetrical, and each end will be the same distance from the last, or first, frame.

Many kayaks are not symmetrical, so there is no reason why front and measurements should match.

Hope this helps.

PGJ