| Summary: | The location of the average roll axis of a ship in water is around the combined center of mass of the ship itself and the so-called added mass of the fluid surrounding it. The location of this combined center is often assumed to be somewhere in the middle between the waterline and the center of mass of the ship, as e.g. in the interim guidelines of the second generation intact stability criteria. These assumptions are approximately valid for deeply submerged ships with low B/T ratios and small bilge radius, but not necessarily for the hull forms of fast, modern roro- or ropax-ferries or other ship types with equal properties. For these ships, the center of added mass and thus the average roll-axis can be located way above the waterline, leading to different accelerations and loads on cargo and personnel on the ship. The paper shows systematically how section wise added mass behaves for certain trends in frame shape and compares numerical results based on strip theory for the location of the roll axis of two different ships with full-scale measurements.
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