Model tests are widely thought as a reliable means of obtaining answers to questions beyond the realm of state-of-the art simulation tools. The author’s experience, no doubt shared with others, has been that whilst providing many answers model tests sometimes raise new questions and unveil phenomena not anticipated at the start. Sometimes these phenomena are investigated in detail and documented (ref [1]), but more often the pressure of project execution prevents enough time to be spent in understanding these phenomena if they are thought to be of secondary importance. This paper will address two such instances of un-resolved and un-explained experimental results. The first instance is drawn from a 2004 model test campaign where an LNG carrier was kept on station by a horizontal mooring in 30m water depth. Un-explained 1st order motion responses were obtained in bow-quartering waves. The second instance is drawn from model tests performed in the context of the HAWAI-JIP in 2006. Un-explained low-frequency sway motions of an LNG carrier were observed during a surge decay tests in shallow water waves. The paper will describe these findings and propose rational explanations.

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