Ship Stability Analysis Quick Reference Guide

Ship stability analysis evaluates how a vessel responds to external forces—such as wind, waves, cargo shifts, or flooding—while maintaining safe upright or controlled inclined positions. Central to this is the concept of hydrostatic equilibrium, governed by the interplay between the ship’s center of gravity (G), center of buoyancy (B), and metacenter (M). Intact stability focuses on initial (small-angle) and large-angle stability, quantified via parameters like GM (metacentric height), righting arm (GZ), and area under the GZ curve; damaged stability extends these analyses to scenarios involving compartment flooding, requiring probabilistic or deterministic assessment per SOLAS Chapter II-1. Regulatory frameworks—including IMO’s International Code on Intact Stability (2008) and the IBC/IGC Codes—mandate minimum stability criteria across operational profiles (e.g., ballast, laden, heavy weather). Practitioners use tools such as hydrostatic curves, cross-curves of stability, and computerized stability software (e.g., NAPA, Maxsurf Stability) to generate compliance reports, conduct loading condition checks, and support emergency response planning. Real-time applications include pre-departure stability verification, voyage planning with variable draft and KG, and post-incident forensic analysis of stability failures.