Utilizing marine currents for electricity generation could offer a distinct advantage over other renewable energy sources due to the regular and predictable nature of the resource. This paper details the design of a horizontal axis Marine Current Turbine using 2D aerofoil data and a blade element momentum software package. Tidal current data from the Race of Alderney situated in the Channel Islands is used to run simulations of the turbine over various flow regimes and yield the energy capture with time. The results of the simulations are combined with an analytical method that details the layout and energy capture potential throughout a large-scale array. Several array configurations, sizes, and the impact of spacings (between rows and turbines) on the velocity distribution were considered in the analysis. The optimum configuration predicted an annual energy output of 1340 GW h at a rated array capacity of approximately 1.5 GW.