How does increasing a vessel's draft affect its curve of statical stability?

Increasing a vessel's draft has a significant impact on its curve of statical stability, which is illustrated by the GZ curve—the graph of righting lever (GZ) against the angle of heel. As draft increases, the center of gravity (G) and the center of buoyancy (B) also change, leading to alterations in the stability characteristics of the vessel.

When draft increases, the center of buoyancy moves up, and the righting arm (GZ) at any given heel angle tends to decrease. This results in the GZ values plotting lower on the graph, effectively shifting the entire curve downward. A lower GZ means that at various heel angles, the righting moment that the vessel can exert is reduced compared to its previous draft.

Understanding this downward shift is crucial, as it indicates that the stability of the vessel has decreased, which can be a critical factor for safe operations at sea, especially in conditions where a vessel might experience heeling due to waves or wind. The downward shift in the GZ curve can lead to a higher risk of capsizing if the vessel is subjected to sufficient external forces while at a deeper draft.