Influence of Draft on Wave Steepness Effect In the Dynamics of Semisubmersibles

Abstract

This paper reports on an extensive tank test program performed on a modal representative of a typical modern semisubmersible drilling vessel. Specific response values obtained in this study apply only to the configuration_and mass c~ar acteristics of the model tested. However, the general conclusion of the study is that wave steepness effects can be important, and this finding is of significance for all sucn configurations to be certified for operation in severe seas. Distinct nonlinearities were found at drafts of 70, 60, and 50 ft. There were test conditions where the heave response ratio was substantially linear, but at other conditions the nonlinearity ranged from moderate to severe. In general, the nonlinearities were more severe at the shallower draft.References and illustrations at end of paper.