Indicators of the critical state of the ship’s stability

Abstract

According to the main criterion, the vessel stability according to the main criterion is standardized by the Rules of the Russian Register by the assumption that the units of the stability margin are practically equal, which is the ratio of listing and restoring moments characterizing the equality of their work. That is, the current domestic and international standards allow the achievement of a shipborne borderline hazardous state, after which it will either capsize, or an uncontrolled inflow of water into the hull and emergency flooding will begin. The characteristics of the vessel that affect stability during its assessment, both at the design stages and during operation, are determined with some error. It is caused by the assumptions of the Rules to the displacement value determination and the coordinates of the gravity center, incomplete compliance with the predicted cruise conditions, due to the ship falling into possible more severe conditions, the construction of a static stability diagram, which is the dependence of the reduced restoring moment on the inclination angle, with a flat waterline, while it is three-dimensional, and other factors related to the vessel’s type and purpose, which are not taken into account when calculating stability. In this paper, we consider a group of such factors, in relation to ships of inland and mixed (river-sea) navigation, the features and reasons for their occurrence, taking into account in verification calculations. A mathematical stability safety factor form, reflecting the expected increments of permissible values, which will improve the safety of the ship, is proposed.