An Investigation of Hydrofoils in the NACA Tank, Benson and Land, Sep 42(0120) Efforts to employ hydrofoils on seaplanes and surface boats have frequently been handicapped by the lack of information on the characteristics of hydrofoils when near the surface of the water or when breaking the surface. In the present tests, a series of hydrofoils, each supported by two struts, was towed at various depths ranging from partial submersions to a depth of 5 chord lengths. Results are presented showing the lift and drag of hydrofoils having a chord of 5 inches, a span of 30 inches, and for angles of dihedral of 0ú, 10ú, 20ú, and 30ú. The tests included speeds up to 95 feet per second, and lift forces up to about 2500 pound. The hydrofoils tested included two sections, the NACA 16-509 airfoil section and a section derived from the 16-509 by sharpening the leading edge.