well since air compresses and water does not, the air would compress to some extent momentarily. how momentarily depends on the hull design, i.e: the amount of opening where the step meets the hull side, also one would have to facter in the compression force vs.the atmospheric shear factor. Thaty being the point where air would more easliy shear and dissapaite into tiny bubbles in the water as opposed to compressing. the angle of entrapment would also come into effect. In any scenerio, the amount of air compressed would not be sufficient to cushion the boat. Also factoring in is that with the angle of the step and the foreward motion of the boat, the air really has no pocket to compress into. to compress into the notch of the step, the boat would actually have to be moving in a somewhat reverse direction.