: Isn't it presumably possible to curve the aluminum stringers enough to allow
: the bow upsweep and use skin tension to maintain a positive upward curve
: (as opposed to a bad downward curve!)?

The problem you run into is the reflex of the tubes if forced to take too
radical a bend. You are correct in assuming that the skin will help hold the
correct shape, as will the cross sections. In addition, the folders sectioned
tubes loose a bit of flex also.

Still, I am careful to avoid too great a bend to all of the tubes. My Aleut
designs have a lot of rocker, but the gunwales are fairly flat to reduce the
overall amount of curvature. Another point to remember is that the even though
some upward stringer curvature will be lost while sitting on the ground, your
folder will get it back in the water with you in the boat. Flex is good !
I transport my folders deck down to retain the designed tube bend. Again,
in the water, they ride as designed.

Most East Greenland Kayaks appear to have little rocker, and fairly flat sheer
lines. They should be fine. I've seen some Greenland designs that could
be a problem due to the excessive flare at the stem/stern. Your Anas Acuta has
lots of rocker if I remember correctly, but I don't recall the shape at the
Gunwales.

Tom