Intact stability of passenger ships : safety issue or design concern? Neither!

Vassalos, Dracos and Atzampos, Georgios and Paterson, Donald and Cichowicz, Jakub and Bertheussen Karolius, Kristian and Boulougouris, Evangelos and Konovessis, Dimitrios; Ruponen, Pekka, ed. (2019) Intact stability of passenger ships : safety issue or design concern? Neither! In: Proceedings of the 17th International Ship Stability Workshop. Aalto University, Helsinki, Finalnd, pp. 333-339.

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    Stability has been a primary focus of the maritime industry and of immense interest to the IMO from the outset. Despite several attempts to resolve stability-related issues, the problem of stability remains one that has yet to be resolved. Reasons for this, range from the complexity of the problem itself to misconceptions in its very nature, particularly concerning intact or compromised conditions of the ship in question. Emphasis in this paper is placed on the latter. More specifically, whilst intact stability of ships is an extremely interesting scientific problem, to what extent is it a determining factor in the design and operation of passenger ships? Currently, intact stability and damage stability share the same stage from a regulatory perspective and, consequently, they have equal impact on design and operation-related decisions, an example of which is the use of combined intact and damage stability GM limit curves (e.g. IACS Rec 110 Rev1). However, in line with goal-based regulations and standards, design and operational decisions should be risk-informed in which case, matters relating to damage stability are of higher concern, simply by virtue of the fact that damage stability is by far the greater risk contributor. In fact, for passenger ships (>500GT), the level of risk associated with intact stability is indiscernible in contrast to that of damage stability. More importantly, in the operational loading conditions of such vessels, damage stability is a more dominant constraint. Hence, such ships can be designed on the basis of damage stability considerations alone. This paper delves in this direction by drawing on the current regulation-making process for risk estimation as adopted by IMO as well as current design and operational practice. Findings from European research and related studies are provided in order to substantiate the argument that intact stability for passenger ships is neither a safety issue nor a design concern.