Towards real-time identification of initial stability from ship roll motion analysis

Stability related failures are known to represent an important cause of accidents involving fishing vessels, and are usually related to the crew lack of capability for assessing the stability level of their ships in an objective way. The use of simplified guidance systems could be adopted as a possible risk control option for trying to address this problematic situation. However, the need for manual interaction with the crew, is one of the major drawbacks of such systems. In this paper, a sample application of a methodology based on spectral analysis of roll motion for obtaining the natural roll frequency of the vessel is presented. The final intention is to have a tool which, from roll frequency estimation, could be used for the estimation of initial ship stability characteristics. The proposed methodology is tested by using roll motion results from a nonlinear one degree of freedom roll model, under the excitation of beam irregular waves and lateral gusty winds. The obtained results are promising, but some open aspects, relevant to the real application of such approach, require further discussion and investigation.