The purpose of our study is to numerically analyze the aerodynamic characteristics of multiple wing sails which have three identical wing sails in a row and optimize their shape and operation conditions in terms of the flap length, deflection angle and angle of attack under various wind directions. A viscous Navier-Stokes flow solver is used for the numerical aerodynamic analysis. A design optimization framework using an evolutionary algorithm and the Kriging surrogate model is developed and finds the optimum solution for multiple wing sails to maximize the thrust coefficient. A total of nine design variables are employed, and relative wind direction, which is allowed to vary from 45 degrees to 90 degrees and 135 degrees. The design results are validated using a three-dimensional Computational Fluid Dynamics analysis. The validation results show that the average thrust performance of optimized multiple wing sails was improved in all wind directions in comparison With the baseline multiple wing sails. (C) 2016 Elsevier Ltd. All rights reserved.