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Some fatal accidents occurred to vessels in loading conditions characterized by large metacentric height indicate that such loading conditions could lead to problems from a safety perspective. The issue has been addressed in the framework of International Maritime Organization (IMO) Second Generation Intact Stability Criteria (SGISC) by introducing “excessive accelerations” as a specific failure mode. However, safety-oriented studies in this respect are still not numerous, and further data for IMO SGISC development are also needed. Therefore, this paper addresses the behavior at sea of a container vessel from a safety perspective, using nonlinear time domain ship motion simulations. Two loading conditions are considered, where one of the two is characterized by a relatively large metacentric height. Human-related and systems&machinery-related hazards, which are linked to ship motions through appropriate failure conditions, are taken into account. Short-term and long-term safety level indicators determined for the two considered loading conditions are compared and discussed.

In this paper a specific procedure for the structural assessment of a container stack is implemented to a realistic case in order to evaluate its effectiveness in the prediction of the operational limits of a container vessel. The feasibility of an extensive calculation based on such procedure is tested, paving the way to the direct analysis of a container stack subject to the inertial loads arising from the ship motions. The procedure is based on a 3D non-linear FE analysis coupled with a direct simulation of non-linear ship motions for the determination of inertial forces acting on a container stack. A non-linear approach has been used for modelling both the ship motion response and the container stack structural response, leading to a global large amplitude analysis. A simplified model of a container stack has been defined in order to decrease the computational cost of the structural calculations, allowing for a use in the framework of an extensive analysis considering many different ship sailing conditions. As final results, diagrams showing the occurrence of failure of container structures or lashing equipment are presented.

To assess the safety of people and cargo onboard, severe environmental conditions are to be taken into account. In such conditions it could be necessary to use tools allowing the simulation of the nonlinear behaviour of a vessel free running and manoeuvring in waves. The need for applying such advanced tools in certain situations is one of the outcomes of the IMO discussion on the development of Second Generation Intact Stability Criteria, and, in particular, regarding tools for “Direct Stability Assessment” and for the development of ship-specific operational guidance. Within this context, a nonlinear time domain simulation tool is applied in this paper for the case of a container vessel. Simulations have been carried out considering the vessel free running in irregular waves. A set of conditions have been specified for identifying human-related, systems&machinery-related and cargo-related failures from time domain simulations. Some results are reported and discussed.