Seakeeping Model Tests of a Platform Jacket Tow

Abstract

This paper describes the results of seakeeping model tests of an offshore platform jacket tow. The 3000-ton jacket was fabricated in Labuan, Malaysia and towed on a launch barge across the Pacific to its final destination, offshore California. The model tests include: 1) Stability tests in regular and random beam seas, and 2) Motion tests in regular and random beam and head seas. Two different launch barges were modeled, and the barge-jacket combinations was tested with and without bilge keels on the barge. The motion test results indicate significant reductions in roll motions with bilge keels. In contrast, the stability tests indicate only marginal improvement with bilge keels. In order to correlate with theoretical results, which do not include the effect of jacket leg submergence during motions, tests were conducted with and without jacket leg submergence. Submergence of the jacket legs results in significantly greater capsizing wave heights, indicating that deck cargo can favorably influence stability. The motion tests, however, indicate that motions in low to moderate seas are not significantly affected by jacket leg submergence. The model test results are compared with analytical results obtained using a computer program based on strip theory. The comparisons indicate that there is reasonable correlation in irregular seas. In regular seas, the results for pitch motions compare more favorably than those for roll motions.