I'm not sure I understand your statement regarding aluminum flex and it's performance on ocean vs. inland waters. {snip}

Hi Tom,

I have built an ash-tree iqyax (6aügàpka) and the flex of the 16,5 mm stringers just amazed me. I'm now building an alu tubing kayak.
Perhaps you've seen a Klepper or Nautiraid vendor at a boat fair kick a bilge stringer to show how they're strong.
The square (actually rectangular) section also permits more bend.
It seems to me that a tube, due to its shape, is generally stiffer.
Remember hollow masts, wood or aluminium. I've been told that a wooden hollow mast (coming in two halves) is sronger than a solid one.
As for sea flexibility, I was referring to Inuit (as well as Aleut) designs, that rely on a huge flexibility to cope with ocean waves.
I don't mean it isn't needed in the middle of Lake Powell when the wind starts picks up! Only implying that flat water, if such a thing exists, call for less flex.
All things relative, anyway. Comparing oranges (full ash squarish stringers) to apples (hollow alu tubes) is a problem.
I'm sure your own yaks are flexible, as you use thin tubing and tube diameters as small as 15 or 14 mm if I'm about right.
Using such small stringers supposes to add more stringers to the basic six.
Voilà.

Btw, I've started a folding sailboat project, like the Master or Mewa on the site below; such dinghies have -heavy- ash stringers, and I'd like to replace them with alu tubes.
So far, I've found that impossible, considering the flex needed by the beam that's twice a large yak's beam, and, much more, because of the torque of the mast-leeboard axis that pulls on the structure.
Some people have noticed that part of that pull is absorbed -compensated for- by the flexing of the ash woodwork as the aft of the boat can be seen resting evenly on the water while the mast is heaving on a tack.
If you have an opinion on this, I'd' be glad to know about it.

All the best

Eric