How should you calculate the Gm of a vessel from her rolling period?

Calculating the metacentric height (Gm) of a vessel from her rolling period is most accurately done by averaging as many full rolling periods as possible. This approach minimizes the influence of temporary disturbances or anomalies that can occur during any single measurement. By taking multiple full rolling periods, you obtain a more reliable average that enhances the precision of your calculations.

Additionally, rolling periods can be affected by various factors such as wave action, wind conditions, and the vessel's loading condition. Averaging multiple periods helps to smooth out these variable influences, giving a clearer picture of the vessel's stability characteristics.

In contrast, measuring just one single rolling period may lead to inaccuracies due to transient effects, while measuring only around noon constrains the data collection and might not represent the vessel's behavior consistently throughout other times of the day. Conducting measurements during rough seas could also skew results, as challenging conditions can produce erratic rolling periods that don’t accurately reflect the vessel’s stability. Thus, a comprehensive approach using multiple data points is advantageous for a definitive calculation of Gm.