Column stabilized semisubmerged drilling vessel

Abstract

The vessel comprises a pair of laterally spaced elongated hulls having a pair of upstanding columns at opposite ends thereof supporting a working platform and a drilling mast in spaced relation above the hulls. The hulls buoyantly support the vessel in a low draft in-transit floating condition with the hulls having freeboard. The hulls have ballast compartments to submerge the hulls and portions of stabilizing columns such that the waterline lies intermediate the height of the columns with the platform and drilling mast elevated above the waterline. The columns stabilize the vessel in the high draft condition and the number, cross-sectional area and configuration of the columns, the weight distribution of the vessel and the geometry of the submerged hulls and portions of the columns are such that the vessel obtains motion minimizing characteristics in the high draft condition. Various features include hydrostatic and geometric properties wherein the ratio of the righting moment about the pitch axis to the righting moment about the roll axis in high draft condition is within a range of 1.0 to 1.3 while the ratio of vessel length to width lies within a range of 1.2 to 1.5; a natural period in heave in a range of 16-18 seconds; and a heave response amplitude operator in a range of about 0.35 to 0.60 in the range of waves of 10-14 seconds.