The Boeing Jetfoil Model 929-115 hydrofoil ship was derived from Model 929-100, with increased forward foil area larger load-carrying capacity. Forward and aft foil contours were revised to increase cavitation margin. New hydrodynamic design methods were employed to maximize foil thickness for minimum structural weight. Prediction of foilborne cruise performance was based upon theoretical analysis, model test data, and full-scale trial data from Model 929-100. Extensive flowfield observations were made of the foil systems during sea trials of the first Model 929-115 produced. Good agreement was found between predicted and observed cavitation and ship performance characteristics. Sensitivity of ship performance to operating variables was determined from sea trial data.