Session: 06-12-01 Ship Hydromechanics I

Paper Number: 78781

78781 - On the Influence of Hull-Shape on the Location of Roll-Axis 

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. The assumption behind this is, that the added mass of the sway motion is assumed to be of roughly equal magnitude as the mass of the ship itself, and that the acting point of the inertia force exerted by the fluid on the ship’s hull, the center of the added mass, is located around the waterline. 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 ro-ro or ro-pax ferries or other ship types with equal properties. For these ships, the center of added mass and thus the average roll-axis is can be located way above the waterline, leading to different accelerations and loads on cargo and personnel on the ship. The paper shows results of numerical calculations based on strip theory and from measurements in full-scale, where a set of two inertial measurement units was used to determine the location of the average roll-axis.

Presenting Author: Lars Johnsen Hamburg University of Technology

Authors:

Lars Johnsen Hamburg University of Technology
Stefan Krüger Hamburg University of Technology