Abstract: A semi-submersible offshore vessel including a rectangular ring-pontoon having a first transverse pontoon section at a first end of the vessel and a parallel second transverse pontoon section at a second end of the vessel, and two parallel pontoon sections extending between the first and the second end of the vessel. Four support columns extend upwardly from respective edge-portions of the ring-pontoon to support an upper deck structure. The first pontoon section has a vertical mean cross-section area (A) which exceeds the corresponding vertical mean cross-section area (B) of the second pontoon section, and the support columns in the second column pair each has a water-plane area (F) which exceeds the water-plane area (D) of each of the support columns in the first column pair.

Abstract: A semi-submersible offshore vessel (1) exhibiting a first end (2), for example constituting the forward end of the vessel, and a second end (4), for example constituting the aft end of the vessel (1), or vice versa, wherein the vessel (1) includes a substantially rectangular ring-pontoon (6) including a first transverse pontoon section (10) located at the first end (2) of the vessel (1); a second transverse pontoon section (12) located at the second end (4) of the vessel (1), the second transverse pontoon section (12) being parallel to the first transverse pontoon section (10), the ring-pontoon (6) further including two mutually parallel longitudinal pontoon sections (14) extending between the first (2) and the second end (4) of the vessel (1); at least four support columns (16, 18, 20, 22) extending upwardly from respective edge-portions (23) of said ring-pontoon (2), the support columns (16, 18, 20, 22) being arranged in a first column pair (24) located at the first end (2) of the vessel (1) and a second co