Motions of jackup drill rigs in head seas 1

Abstract

Previous predictions of barge motions in head seas are extended to include forces and moments on cylindrical legs in order to analyze wave-induced motions of jackup drill rigs in the transition phase while the legs are being lowered. Predicted motions for a typical jackup drill rig in head seas with legs up, half down and full down (but not touching the ocean bottom) are shown to be in good agreement with corresponding scala model test results. It was found that the major effect of the legs is to modify the inertia of the vehicle while the damping effect of the legs is small and for practical purposes can be represented by the theoretical motion-induced damping force and moment.