Abstract: A buoyant substructure to float upright in water (e.g. for an offshore platform) and comprising at least three spaced apart columns [103] joined together in generally aligned relationship, in which at least one of the columns is adapted to be ballasted at its end [107] which is to float low down in the water, in which the columns are joined together by discrete cross members [111,113] which are widely spaced apart along the length of the columns, and in which the discrete cross members [111,113] have relatively small dimensions in the direction of alignment of the columns as compared with the total length of the columns.

Abstract: A floating platform comprising in combination a semisubmersible vessel (40) having two or more pontoons, buoyant columns upstanding from those pontoons and a deck supported on the columns (the semisubmersible vessel being a kind known per se); and a raft (41) comprising a hull portion and two or more buoyant caissons arranged so that the raft is capable of floating in a stable configuration with the hull portion of the raft submerged to such a depth that the semi submersible vessel (40) can float over the hull portion and with only the buoyant caissons piercing the water surface, in which the pontoons of the semisubmersible vessel (40) are secured to upper surfaces of the hull of the raft (41).