This paper describes the technical feasibility study and the economical evaluation of the floating wind power system. The box-girder type floating structure installed three wind turbines is proposed as a concept. The 5MW class propeller type turbines are adopted. The box girder with simple structures is favorable in the cost performance. Moreover, the wave induced motion and the righting moment can be optimized easily. The estimations of the static inclination and the wave induced motion were carried out in technical study. The relations between wind loads and motions or inclinations were investigated by the wind tunnel test. On the numerical analysis of motions, the fluid dynamic forces were calculated using the potential theory with zero draft assumption in the estimation of motion. The floating structure model was consisted by beam elements of FEM. The calculation result showed that the motion and the inclination in an operation condition are less than 5 degrees. According to the economic estimation, it was presumed that the proposed concept can be attained to the equally cost of water-power generation and others.
