Contours were part of the design for the BYO skis we developed in 2001. They are attached to the outside edges of the bottom of the OEM skis and are aligned with the wear rods.
As a result, floatation and control are improved. Instead of the snow squirting/pushing to the outsides of the ski, it is trapped between the 3/8" tall contours and the keel. The compacted snow crystals interlock with the deeper snow crystals, performing both functions.
updated 7 screw version