Column stabilized semisubmersible pipelaying barge

Abstract

The pipelaying barge comprises a pair of laterally spaced, elongated hulls having a plurality of upstanding columns spaced therealong supporting a working platform in spaced relation above the hulls and on which platform is carried a pipe section assembly line and one or more cranes movable longitudinally along the platform and capable of servicing the pipe section assembly line. The hulls have ballast compartments to submerge the hulls and portions of the stabilizing columns to a high draft condition with the mean waterline at a necessary and desirable locus intermediate the height of the stabilizing columns. A transition segment is connected to the stern of the barge for support of the 'air length' segment of the pipeline between the stern of the barge and the point of entry of the pipeline into the water and preferably also supporting a short segment of pipeline in the water as the pipeline is payed out from the barge. To lay pipe, the pipelayer barge is disposed in the high draft condition and ballasted to provide a preset angle of trim. The attitude of the barge in trim about the pitch axis when in high draft pipelaying condition is maintained within an angle not in excess of plus or minus one-half degree of the preset trim to avoid introducing undesirable pipe stresses due to change in the attitude of the barge in trim about the pitch axis caused by longitudinal movement of one or more cranes; further, change in trim angle exceeding plus or minus one-half degree is offset by ballast correction correlated to longitudinal location and movement of the crane to maintain the barge trim within plus or minus one-half degree of the preset trim angle whereby pipelaying and crane operations can be performed simultaneously without interruption.