The first thing that should come to your mind upon studying this photo is that THERE ARE

NO VERTICAL STIFFENERS on the diagonal ribs!  In spite of Professor Avery's good advice,

Molt chose to pass it along to others but not to heed it himself. Note that Mike has

already spliced the lower cap on this diagonal rib before installing the vertical stiffeners. 

If you need more information on this issue, see pages 14 and 19 of The Coot Story.