Author Description

This task reviews the ultimate stability of a heavy concrete platform under tow along the west coast of the United States. Two hull configurations of the platform are assessed for their seaway thresholds based on their static stability curves and dynamic performances. The dynamic performances are determined with a time domain simulation model built on a large amplitude motion scheme that closely tracks the instant wetted hull shape and fluid forces including viscous damping. Heavy seas heave the platform wildly and occasionally engulf the entire platform of both configurations. Simulation results indicate that the platform as designed may capsize in low sea state 5. The capsizing is largely attributed to a total loss of static stability due to severe deck immersion that allows the platform to heel extensively and eventually capsizes. The same platform with a quadruple freeboard extends its operation window substantially to Sea State 7. The stability assessment procedure and its rational basis are documented.