A spar platform comprises one or more continuous-fiber composite tubes fabricated at or near the intended site use of the platform. In some embodiments, the spar platform includes a relatively longer central tube and relatively shorter peripheral tubes. In some other embodiments, the spar platform is a single long tube. In some embodiments, the spar platform supports a wind turbine assembly. The continuous-fiber composite tubes are formed, in either a vertical or horizontal orientation, using a modified vacuum assisted resin transfer molding process.