A watercraft (99) having a stepped hull (100) including a forward hull portion (103), a first stepped hull portion (106), and optionally a second stepped hull portion (108). Outboard ram air fins (120) extend outwardly from the hull and downwardly along the stepped hull portions. Outboard strakes (110, 112) are fixed to the stepped hull portions, and may be tapered to define ports thereto. During planing operation the channels defined by the fins compress the incoming air which is thereby at least partially forced under the stepped hull portion. In level operation the flow through the channels tends to keep the stepped hull portions in good contact with the water.