Numerical simulation of wake losses is a fundamental step towards the optimization of the exploitation of the renewable wind energy potential especially in off-shore conditions or in coastal areas. The scientific community is quickly developing new advanced modelling techniques in order to improve the reliability of power losses calculation in many different kinds of environment; analytical models are going to be replaced by new Computational Fluid Dynamics (CFD) codes that seem to be more useful, especially for large offshore wind farms. In the present work an actuator disc model was implemented in order to simulate the wakes of a wind farm; this model was used within the CFD code PHOENICS (the numerical core of the Windsim package) working with an orthogonal Cartesian grid. The model was validated using real production data from a small wind farm operating in the western coastal region of Finland; the numerical wind speed profiles were verified using anemometer data from a mast placed near the turbines. The results demonstrate that, despite its simplicity, the actuator disc model can give very useful information when developing a wind farm in off-shore or coastal areas. This work was carried out within a cooperation between the Department of Industrial Engineering of the University of Perugia and VIT, the technical research centre of Finland. (C) 2012 Elsevier Ltd. All rights reserved.