Heybwd, I am not sure you understand boundary layer term correctly, or maybe you do but you simply described youself wrong here. Boundary layer over the wing airfoil is the extremely thin layer or air which sticks t the airfoil and the one which is the main layer to create lift. Usually, boundary layers are laminar and they detaach from the wing at close to the midpoint of the airfoil. The trailing edge of the wing thus does not create lift and neither is it very useful for the wing. The trailing edge cretes wake drag, it is turbulent, and is a place for stall areas on the wing. Although, the trailing edge we need for LESS wake drag, since it's sharp edge which serves as the final point back along the airfoil provides a good detachment point for the air.

I think what you mean by "the boundary layer is amde thicket with turbulators" is the boundary layer is PROLONGED, thus increasing the wing efficiency- which is especially important to sail planes as BMatthews pointed out there- with a wing of better efficiency the sail plane would be more likely to stay at an altitude during no wind or rising current, but relying only on it's speed and the gravity.

Correct me if I am wrong, but I am pretty sure I am right since I read this boundary layer stuff from a good aerodynamic book written by a well experienced aerodynamicist and engineer.

Yishht87.