A column stabilized semisubmersible vessel consisting of a pair of elongated hulls disposed in substantially parallel spaced side-by-side relation with each of said hulls spaced from and lying on an opposite side of the longitudinal centerline of said vessel, said vessel further comprising:
- a working platform spaced above said hulls a predetermined height;
- means for supporting said platform in fixed spaced relation above said hulls, including four stabilizing columns connecting said hulls with said platform;
- one pair only of said stabilizing columns being connected with each of said hulls on opposite sides of the vessel roll axis, with one column of each said pair being located near respective opposite ends of each hull on opposite sides of the pitch axis of the vessel;
- each of said stabilizing column having a substantially rectangular and substantially constant cross-section over the effective column height extending between the topside of the hulls and the underside of the platform;
- each rectangular cross-section column including two pairs of substantially vertical substantially parallel substantially planar sides, with one pair of sides extending longitudinally of the vessel substantially perpendicular to the vessel's pitch axis;
- said working platform including a plurality of substantially vertical plates extending transversely of the vessel substantially perpendicular to the vessel's roll axis, with one of said plates being substantially in alignment with each of said rectangular column's sides extending transversely of the vessel;
- said working platform including a plurality of substantially vertical plates extending longitudinally of the vessel substantially perpendicular to the vessel's pitch axis, with one of said plates being substantially in alignment with each of said rectangular column's sides extending longitudinally of the vessel;
- the ratio of the length of said vessel along its longitudinal centerline to the width of said vessel along its transverse centerline being within a range of 1.2 to 1.5;
- means for ballasting said vessel, including ballast compartments in said hulls, to alter the vessel's draft between a low draft hull-supported floating condition with the hulls having freeboard and a high draft semisubmerged column stabilized floating and operating condition with mean water-line located intermediate the height of said columns;
- said columns being of predetermined cross-sectional areas and location so as to provide a ratio of righting moment about the vessel's transverse pitch axis to righting moment about the vessel's longitudinal roll axis within a range of 1.0 to 1.3 when said vessel is in high draft semisubmerged operating condition;
- each of said hulls for at least substantially the major portion of its length being of substantially rectangular cross-section and consisting of a pair of substantially equal substantially horizontal substantially parallel substantially planar surfaces and a pair of substantially vertical substantially parallel substantially planar surfaces, with breadth of each hull cross-section in horizontal direction being greater than vertical height of each hull section;
- each said hull including a plurality of substantially vertical bulkheads extending transversely of the vessel substantially perpendicular to the vessel's roll axis, with one of said bulkheads being substantially in alignment with each of said rectangular column's sides extending transversely of the vessel;
- the width of the vessel at the hulls in relation to the transverse spacing between said rectangular hulls being within a range of 1.5:1 to 2:1;
- a plurality of longitudinally spaced structural means reinforcing the structural relationship of the hulls, platform and columns;
- said structural reinforcing means including a plurality of trusses, each truss located longitudinally of the vessel at a position adjacent one of said rectangular columns's sides extending transversely of the vessel;
- and each truss including transversely extending members structurally interconnecting uppermost portions of said hulls;
- said vessel comprising means including said columns of predetermined cross-sectional area, said transverse spacing of the hulls one from the other, vessel displacement, and geometry of the submerged portions of the vessel in high draft column stabilized semisubmerged operating condition being such as to provide a vessel response curve having a "low wave period section", a "first hump", and a "third section" with an "RAO" in relation to wave period "T" according to the following mathematical relationships:
- (i) the RAO value of the curve's "first hump" is not greater than 0.6 for values of T between about 10 to 14 seconds;
- (ii) the "third section" of the curve has a natural period value of between about 16 to 18 seconds.