That's the new 2 piece trench/plug full cover. It completely fills all voids so doesn't fill with water and still gives minor adjustment on mast placement. Working on commercial version right now with Dale to fit all brands of mast , it was pretty well impossible to do the one piece full cover that I've been using . This works incredibly well , the starts are so easy now as you can see in the video .No wave assist or paddle strokes required on a 690 cm 2 that's pretty cool in my books.