What change in the natural roll period occurs with a GM of 0.30m?

The natural roll period of a vessel is directly influenced by its metacentric height, denoted as GM (the distance between the center of gravity and the metacenter). A GM of 0.30m indicates a relatively low metacentric height, which can have a significant impact on the dynamics of the vessel's roll motion.

When GM decreases (as in the case of a low value like 0.30m), the roll period tends to lengthen. This is because a lower GM means that the vessel has less initial stability, causing it to take longer to right itself after being tilted. As a result, the natural roll period becomes extended, leading to slower rolling motions. This dynamic is critical in understanding how stability affects vessel performance, especially when considering factors such as cargo loading and weather conditions.

In this context, the correct answer illustrates the principle that a lower GM correlates with a longer roll period, impacting the ship's stability behavior during operations.