This paper describes an experimental and numerical study on the effect of bilge keels on a specific offshore vessel. Forced roll and free decay experiments were carried out at MARINTEK in a joint project between VARD, DNV GL and MARINTEK during Nov. 2012. The 1:25 ship model was tested both with and without bilge keels. 19 forced roll periods were tested at 4 roll angles (2, 4, 6 and 10deg). Free decay tests were performed for initial roll angles 2, 4, 6, 10 and 15deg. Damping was extracted and compared with numerical simulations from a potential flow strip theory program (VERES) and a commercial CFD tool (StarCCM+).

Both qualitative and quantitative agreement between the experimentally and numerically obtained damping parameters was documented. Discrepancies were identified and discussed. The three different methods of investigation gave together a basis for discussing the effect of bilge keels. From the present study, it is recommended that both experimental and numerical work in combination, for both forced roll and free decay tests, should be performed to assess the damping efficiency of bilge keels.

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