Semi-submersible floating offshore vessel

Abstract

A semi-submersible floating offshore vessel has a deckbox structure with a main deckbox bottom extending underneath a lower deck. The deckbox structure includes a recessed cellar deck structure that protrudes below the main deckbox bottom, which recessed cellar deck structure has a cellar deck bottom wall that is closed and wave impact resistant and which recessed cellar deck structure has a peripheral wall that is closed and wave impact resistant. The peripheral wall extends between an outer perimeter of the cellar deck bottom wall and the main deckbox bottom of the deckbox structure. The moonpool extends through the recessed cellar deck structure. Seen in plan view, the recessed cellar deck structure includes a number of pointed wave crest splitting sections.

1 - 16 . (canceled) 
     
     
         17 . A semi-submersible floating offshore vessel, said vessel comprising:
 a deckbox structure;   one or more buoyant pontoons; and   multiple buoyant support columns projecting upwards from the one or more buoyant pontoons and supporting thereon the deckbox structure;   wherein the deckbox structure comprises an upper deck, a lower deck, and a main deckbox bottom,   wherein the main deckbox bottom extends underneath said lower deck, the main deckbox bottom being closed and wave impact resistant, and the main deckbox bottom connecting to the buoyant support columns,   wherein a moonpool extends through said deckbox structure, said moonpool having a lower moonpool opening,   wherein, seen in a plan view, multiple of said multiple buoyant support columns are arranged around the moonpool, so that a pair of adjacent buoyant support columns define an intercolumn space therebetween,   wherein the deckbox structure comprises a recessed cellar deck structure that protrudes below the main deckbox bottom, the recessed cellar deck structure having a cellar deck bottom wall that is closed and wave impact resistant, and the recessed cellar deck structure having a peripheral wall that is closed and wave impact resistant, wherein the peripheral wall extends between an outer perimeter of the cellar deck bottom wall and the main deckbox bottom of the deckbox structure,   wherein the moonpool extends through the recessed cellar deck structure, wherein the cellar deck bottom wall delimits the lower moonpool opening, and wherein a cellar deck of the recessed cellar deck structure adjoins the moonpool,   wherein, seen in a plan view, the recessed cellar deck structure comprises a number of pointed wave crest splitting sections corresponding to the number of intercolumn spaces defined by the buoyant support columns arranged around the moonpool,   wherein each pointed wave crest splitting section has, seen in plan view, a tip remote from the moonpool, and diverging peripheral wall sections, and   wherein each pointed wave crest splitting section is directed with the tip thereof to a respective intercolumn space.   
     
     
         18 . The semi-submersible floating offshore vessel according to  claim 17 , wherein the air gap of the recessed cellar deck structure is between 12 and 15 meters. 
     
     
         19 . The semi-submersible floating offshore vessel according to  claim 17 , wherein the recessed cellar deck structure protrudes below the main deckbox bottom over a height between 2 and 5 meters. 
     
     
         20 . The semi-submersible floating offshore vessel according to  claim 17 , wherein the vessel has four buoyant columns supporting the deckbox structure vessel, and the cellar deck structure has four pointed wave crest splitting sections. 
     
     
         21 . The semi-submersible floating offshore vessel according to  claim 17 , wherein the moonpool is offset from a geometrical center of the deckbox structure. 
     
     
         22 . The semi-submersible floating offshore vessel according to  claim 17 , wherein the vessel has three buoyant columns supporting the deckbox structure vessel, and the cellar deck structure has three pointed wave crest splitting sections. 
     
     
         23 . The semi-submersible floating offshore vessel according to  claim 17 , wherein the diverging peripheral wall sections of one or more of the wave crest splitting sections have an outward flare, outwardly inclined relative to vertical from the lower edge of the wall section to the top edge that adjoins the main deckbox bottom. 
     
     
         24 . The semi-submersible floating offshore vessel according to  claim 17 , wherein each wave crest splitting section has a substantially planar bottom wall portion forming part of the cellar deck bottom wall to which the diverging peripheral wall sections join along their lower edges. 
     
     
         25 . The semi-submersible floating offshore vessel according to  claim 17 , wherein the vessel comprises a drilling installation with a drilling tower erected above the upper deck of the deckbox structure and adapted to perform wellbore related operations along one or multiple firing lines through said moonpool. 
     
     
         26 . The semi-submersible floating offshore vessel according to  claim 25 , wherein the vessel comprises a BOP transport system, the BOP transport system comprising:
 a BOP track arranged on the cellar deck and having a set of parallel BOP handling cart rails extending from a BOP storage area towards and along opposite sides of the moonpool; and   a BOP handling cart, the BOP handling cart being movably supported by the BOP handling cart rails, for travelling over said rails so as to allow for transfer of a subsea BOP between a BOP storage position, in which the BOP is located at the BOP storage area, and a BOP launch position, in which the BOP is located in the moonpool and aligned with a firing line.   
     
     
         27 . The semi-submersible floating offshore vessel according to  claim 25 , wherein the vessel comprises vertically oriented wireline riser tensioner cylinders that are mounted in vicinity of the moonpool and arranged between the upper deck and the recessed cellar deck bottom wall, wherein the vessel comprises a first set of vertically oriented wireline riser tensioner cylinders arranged along one side of the moonpool, and a second set of vertically oriented wireline riser tensioner cylinders arranged along an opposite side of the moonpool. 
     
     
         28 . The semi-submersible floating offshore vessel according to  claim 25 , wherein the vessel is provided with a vertically mobile working deck arranged in vertical projection above the moonpool, the working deck being vertically movable. 
     
     
         29 . The semi-submersible floating offshore vessel according to  claim 28 , wherein multiple vertically mounted working deck compensator cylinders are provided, arranged between the deckbox structure and the mobile working deck, wherein said working deck compensator cylinders are configured to provide a heave compensated motion of the working deck relative to the deckbox structure, and wherein, said working deck compensator cylinders are mounted at a lower end thereof to the recessed cellar deck structure. 
     
     
         30 . The semi-submersible floating offshore vessel according to  claim 25 , wherein the vessel comprises an equipment deck that is located higher than the upper deck of the deckbox structure, wherein the equipment deck is configured for storage thereon of wellbore related equipment. 
     
     
         31 . The semi-submersible floating offshore vessel according to  claim 28 , wherein the vessel comprises an equipment deck that is located higher than the upper deck of the deckbox structure, wherein the equipment deck is configured such that the vertically mobile working deck of the vessel, in a raised position thereof, adjoins the equipment deck allowing for transfer of wellbore related equipment between the equipment deck and the vertically mobile working deck. 
     
     
         32 . The semi-submersible floating offshore vessel according to  claim 25 , wherein the vessel is provided with a shaker room within the deckbox structure and in proximity of the moonpool, wherein the shaker room is on the lower deck, and wherein the vessel is provided with a cutting handling room arranged below the shaker room on the cellar deck. 
     
     
         33 . The semi-submersible floating offshore vessel according to  claim 18 , wherein the recessed cellar deck structure protrudes below the main deckbox bottom over a height between 2 and 5 meters.