A semi-submersible offshore vessel and methods of positioning work modules on said vessels

摘要

A semi-submersible offshore vessel ( 1 ) comprising: a substantially ring-shaped lower pontoon ( 2 ); starboard and port forward columns ( 6 a, 6 b), extending upwards from said lower pontoon ( 2 ); starboard and port aft columns ( 6 c, 6 d) extending upwards from said lower pontoon ( 2 ), and an upper deck structure ( 8 ) connecting upper portions ( 10 ) of the columns ( 6 a, 6 b, 6 c, 6 d) with each other, said upper deck structure ( 8 ) having a substantially rectangular module recess ( 12 ) for receiving one or more operation modules ( 14 ), for example carrying hydrocarbon processing equipment. The invention is especially characterized in that said upper deck structure ( 8 ) is generally C-shaped, having a forward torsion box ( 16 ) extending transversally between the starboard and the port forward columns ( 6 a, 6 b) of the semi-submersible offshore vessel ( 1 ), and two mutually parallel longitudinal side beams ( 18 ) extending aft from the starboard and port forward columns ( 6 a, 6 b) to the starboard and port aft columns ( 6 c, 6 d), respectively, in such a way that said module recess ( 12 ) exhibits an open aft end ( 20 ), the width of which substantially corresponds to the width of an operation module ( 14 ), and that said module recess ( 12 ) is delimited in a downwardly direction by a substantially planar module deck ( 22 ) which extends between-and interconnects-said longitudinal side beams ( 18 ).