A drag-reducing air chamber is formed under a watercraft when the watercraft is underway. Air enters into the air chamber when the watercraft is moving forward. Supplemental air is introduced into the air chamber by an air scoop mounted to the bow in a first embodiment and in side-mounted air scoops in another embodiment. A one-way valve in an air passageway between the air scoop and the air chamber prevents air from flowing from the air chamber to the air scoop. A pair of elongate rails depends from opposite sides of the hull and defines the sides of the air chamber. Shorter rails may be used in high-speed applications where the bow of the watercraft is lifted from the water.