A method for the hydroelastic design of flexible composite shape-adaptive hydrofoils and marine propeller blades is described and demonstrated. It is applicable to situations in which the component is to adapt its shape to small changes in flow relative to a mean operating condition. The shape-adaptive behaviour of the flexible component results in improved efficiency in comparison to a similar rigid component. Starting from a rigid component, the effect of flexibility is considered so that the component will deform in a desired manner under hydrodynamic load changes. An optimisation procedure is used to iteratively determine the composite lay-up and unloaded shape of the flexible component so that it will achieve the required deformations consistent with the calculated change in performance due to flexibility. The method is demonstrated through two examples, which both highlight the importance of the initial geometry and materials on the overall flexibility that can be achieved.