THE OPERABILITY OF DERRICK BARGES IN CONSTRUCTION OF LARGE OFFSHORE STRUCTURES

Since crane operations are restricted by barge motion, crane operability is a vital factor in the execution of an offshore project. Measurements were taken of the motions of the derrick lay barge "Kuroshio" while in service at the Aga platform construction site at a water depth of 80 m in the Sea of Japan. The measured values were analyzed to show that barge motions -- roll, pitch, heave, etc. -- are the overriding factors in the operation of offshore cranes. The measured values were also used to determine the relation between the motion of a hoisted load and the operability of the crane, the relation between barge motion and the motion of the hoisted load, and the relation between barge motion and prevailing sea conditions. These findings are useful in estimating the rate of barge operation for a particular offshore project and in keeping work at the site under optimum control.