The following thesis presents a stability study of a floating wind turbine platform, composed by two concentric cylinders, for offshore application. The theoretical bases of the linear theory and the derivation of the equation of motion are introduced in the second chapter. The following chapter resumes the results of the research of the optimum dimensions as well as the results of the simulation of the equation of motion of the spar with and without inertial plate. The addition of the inertial plate and the variation of its porosity (depending on the frequency of the incident wave) help to stabilize the structure in a large frequency bandwidth, due to the increment of the added mass coefficient and the consequent reduction of the resonance frequency. With the collaboration of the Centre of Nanotechnology and Smart Materials, CeNTI, a solution to simulate the porosity of the inertia plate is proposed as well as the material for the body of the spar and the plate and all the necessary corrosion treatments due to the seawater. Finally, the future work and all the conclusions of the study are explained in the last chapter.