A prop wash straightening apparatus for increasing the efficiency of propeller-driven watercraft. An elongated outer tubular member open at each end thereof is adapted for connection to the boat or vessel to position said outer member immediately downstream of the propeller and in substantially longitudinal fixed alignment with the direction of axial thrust produced by the propeller. A plurality of elongated hollow open-ended inner tubular members are positioned in closely packed fashion within, and generally coextensive with a substantial portion of the length of the outer tubular member. A proximal or forwardly end of the inner tubular members is positioned in close proximity to a trailing plane of the propeller. The outer tubular member extends from the proximal end of the inner tubular members to surround the blade tips of the propeller to direct substantially all prop wash from the propeller into the inner tubular members.