Second Generation Intact Stability Criteria

The Second Generation Intact Stability Criteria (SGISC) are the IMO framework for assessing dynamic stability failure modes that the calm-water criteria of the 2008 Intact Stability Code, Resolution MSC.267(85), do not reach. They were issued as interim guidelines in circular form and are recommendatory rather than mandatory, so they sit above the IS Code as an additional assessment rather than replacing any part of it.

The framework covers five failure modes: parametric rolling, pure loss of stability, surf-riding and broaching, the dead ship condition, and excessive acceleration. Each mode is assessed through a tiered structure that runs from a cheap and deliberately conservative Level 1 screening check, through a more detailed Level 2 criterion, to a direct stability assessment by numerical simulation. A ship found vulnerable at every tier may instead carry operational limitations or ship-specific operational guidance.

The full article will set out the origin of the framework in the IMO Sub-Committee on Ship Design and Construction, the scope and applicability of each failure mode, the tiered assessment logic and why it is ordered as it is, the relationship to the mandatory instrument, the class societies that have published their own application guidance, and the current status of the work to make the criteria mandatory.