The purpose of this paper is to present a semi-analytic model designed to optimize tidal farm layouts by maximizing the mechanical power production. A meta-heuristics method is used to find the turbine placement which minimizes the flow interaction between the turbines. The velocities in the wakes of turbines are simulated with an analytic model. The methodology is first applied to idealized cases: constant current magnitude and direction, and flow aligned with the turbines. Those preliminary tests permit to test the consistency of the results. In particular, they show that the optimal density of the devices grows with increasing turbulent intensities or increasing upstream velocity magnitude. The methodology is then applied to a site located in the Alderney Race (Raz Blanchard in French), situated between the Alderney Island and La Hague Cape (France). The results show that the optimal placement is influenced by the asymmetry of the tidal current and that the best layout is strongly dependent on the directional spreading of the current with respect to the predominant direction.