The design of a floating offshore wind platform must face several challenges, such as minim ising windand wave-induced motion and structural costs. In this paper, a genetic algorithm is used to optimise the main geometric parameters of the floating platform concept 5 MW, 10 MW, and 15 MW Hexafloat for the Pantelleria site. Hydrostatic and time-domain simulations verify the floating stability and dynamic perform ance in terms of dynamic pitch and nacelle acceleration. The optimal structural cost of the platform is reduced by 52% and 22% for the 5 MW and 10 MW wind turbines, respectively, compared to 15 MW, while the LCOE increases by 39% and 11%, respectively. The optimisation tool presented in this work is very effective and can be applied to any other floating platform due to the parameterisation of the mesh geometry.