A material model based on the Puck phenomenological failure criteria for fibre and inter-fibre failure of glass-fibre and carbon-fibre reinforced polymer composites is presented. The model is applied through a user-defined material subroutine for 3D shell elements. Sub-modelling is used for detailed analysis of the highest stressed regions in the blades. The material model is incorporated into a methodology for the design and analysis of composite tidal current turbine blades. The methodology employs an iterative design process with respect to a number of failure criteria to ensure optimal structural and material performance of the blade. The methodology is automated using the Python programming language to enable efficient variation of model parameters for various design conditions. The forces acting on the blades are determined from blade element momentum theory for a number of turbine operating conditions. The results of a design case study for a typical horizontal axis device are presented to demonstrate the methodology.