The purpose of this study is to compare the accuracy of two cost-effective aerodynamic methods used to predict the performance of a large scale wind propulsion system. The methods are evaluated regarding their ability to predict the performance of a configuration consisting of four rigid wing sails of an approximate height of 80 m and average chord length of 23 m. The distance between the wing sails, from trailing to leading edge, is about one chord length. For a limited number of test cases, it is evaluated how well the methods balance computational cost and accuracy and their potential to predict the performance of multiple rigid wing configurations. Two different types of aerodynamic methods are compared; one method under development based on potential flow/lifting line theory in combination with pre-calculated 2D CFD RANS data (CORR-SILL), and a vortex lattice method (VLM). The results from the two different methods are compared with 3D CFD RANS simulations. The parameters compared are the induced velocities around the sails, system forces and longitudinal center of effort. This paper indicates that both evaluated methods show potential to predict the magnitude and distribution of the forces on multiple wing sail, with a large reduction of computational effort compared to CFD.