I dont think the sails are cut with a hollow leech between battens. Look at the pictures here for a better view.

Besides, what would be the design theory behind such a design? I know there has been some research into why some sea mammals have similar profiles on their appendages but have yet to se a conclusive report (more information on this is always welcome).


Take a look at a windsurfer sail with lots of downhaul, you can see the same effect on the shape of the leech there. Hence the conclusion that lots of downhaul was applied. You might even see it on a cat, if you dare to apply enough downhaul and the sail is cut with a large roach.