Tribology in marine renewable technologies has become of increasing interest due to the implications for developing improved materials for tidal and wave energy conversion devices. This on-going research mainly focuses on tidal devices; the materials of interest are primarily polymer-based composite materials that are used to provide structural integrity while reducing weight. These are specifically applied to turbine blades to withstand the high impact loadings in seawater conditions. At present, current materials in test trials have demonstrated some limitations in service. In this paper, some advanced experimental research has been carried out to investigate the tribological mechanisms of potential candidate composite materials to be used in tidal turbines by firstly considering the effects of various erosion parameters on the degradation modes, with and without particles in still and seawater conditions. The erosion mechanisms of composite materials used in tidal turbine blades have been evaluated using Scanning Electron Microscopy techniques to analyse the surface morphologies following testing in water representative of the constituents of coastal seawater. Generic erosion maps and the mechanistic maps have been constructed as a key to identify regions of minimum erosion for the operating conditions and to identify the significant effect of the seawater environment on the degradation of the composite. This research outcome will further help us to deeply understand and identify the erosion rates at different impact velocities and angles.