Free stream tidal turbines are a source of growing interest in the marine renewable energy field. Some designs use variable pitch blade control devices in order to maximize the efficiency of the turbines; however these are complex to design, construct and maintain under the severe load conditions sub sea devices experience. Adaptive materials have been used in the wind industry to create bend-twist coupled blades in an effort to bring turbine efficiency ever closer to the Betz limit, and increase annual energy capture. This work encompasses a feasibility study, focusing on hydrodynamic performance calculations, wherein the blade geometry is artificially reconfigured as a function of flow velocity. The pressure distribution over the blade is also analysed. The concept of a passively adaptive tidal turbine blade is shown to increase annual energy capture, reduce blade loading and delay cavitation inception.