Twin hull semisubmersible derrick barge

A column stabilized semisubmersible barge for marine construction, pipelaying and like other offshore operations, said barge being characterized by:

• 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 barge;
• a working platform spaced above said hulls a predetermined height and normally lying in a generally horizontal plane;
• means for supporting said platform in fixed spaced relation above said hulls including at least three pairs of upstanding columns connecting with each of said hulls and said platform and each of said columns having a substantially constant cross section over the effective height of the column;
• each of said hulls having an oblong transverse cross section with a breadth greater than its height and having top and bottom substantially planar parallel surfaces extending substantially the entire length of each hull;
• a plurality of longitudinally spaced structural means interconnecting and reinforcing the structural relationship of the hulls, platform and columns, with such structural means including substantially transversely extending members structurally interconnecting uppermost portions of the hulls;
• said barge being generally rectangular in plan with the length of said barge along its longitudinal centerline and roll axis being substantially greater than the width of said vessel along its transverse centerline and pitch axis;
• at least three of said columns being located on each of said two hulls on opposite sides of the barge's roll axis with pairs of such columns being located near opposite ends of each of said hulls on opposite sides of the barge's pitch axis and another pair of said columns being located at an intermediate position on each of said hulls;
• each of said columns having an oblong cross section with its dimension extending in the direction of the barge's longitudinal axis being greater than the column's dimension extending transversely of the barge's longitudinal axis;
• the centroid of the cross section of each column being disposed on said hulls outboard of the longitudinal centerline of the associated hull;
• the configuration and cross-sectional areas of said columns throughout effective height thereof and the distances of said columns from the barge's longitudinal roll axis and transverse pitch axis being such that said columns provide sufficient righting moments about roll and pitch axes when the barge is in high draft semisubmerged operating positions and also being such that said columns provide righting moment about the transverse pitch axis which is greater than righting moment provided about said longitudinal roll axis when the barge is in semisubmerged column stabilized operation position;
• crane means located on said barge near one end thereof and mounted for rotation about a normally substantially vertical axis, said crane means being of sufficient size and capacity for various marine construction and other like offshore operations, and having a boom of sufficient length to perform operations off at least one beam of the barge and off the end of the barge near which said crane means is located;
• said hulls having ballast compartments with each of said hulls including a plurality of separate ballast compartments spaced transversely within each hull as well as a plurality of separate ballast compartments spaced longitudinally within each hull;
• means for ballasting said barge when required to alter its draft between a low draft hull-supported floating condition in which the hulls have freeboard with said transversely extending members actually structurally interconnecting uppermost portions of the hulls being disposed above the mean waterline and a high draft semisubmerged column stabilized floating and operating condition in which the mean waterline is located along intermediate portions of said columns between about 0.25 the length of the columns above the tops of said hulls and about 0.25 the length of the columns below the underside of said platform, said intermediate portions of said columns having a substantially constant cross section over an effective height at least above said hull tops and below said platform bottom as aforesaid;
• said means for ballasting including means for adjusting barge angle of heel change caused during semisubmerged column stabilized operations of said barge and crane means to reduce the barge's angle of heel about its roll axis when required during such semisubmerged operations;
• said means for ballasting including means for adjusting barge angle of trim change caused during column stabilized semisubmerged operations of said barge with such crane means to reduce the barge's angle of trim about its pitch axis when required during such semisubmerged operations.