Application of the MMG method for the prediction of steady sailing condition and course stability of a ship under external disturbances

For the navigation safety of ships, it is essential to monitor the maneuvering characteristics under external disturbances due to wind and waves. For this purpose, evaluating the average steady sailing conditions such as check helm, speed drop, hull drift angle, etc. of a ship moving straight in steady wind and waves is beneficial. In addition, the dynamic stability (course stability) of the ship should be evaluated under its steady sailing condition. This study proposes a method for predicting the steady sailing conditions and course stability under external disturbances, based on the MMG standard method presented by Yasukawa and Yoshimura (J Mar Sci Technol 20(1):37-52, 2015). The calculation accuracy of the MMG method has been validated through experiments. The steady sailing conditions and the course stability of a pure car carrier are calculated using the proposed method under external disturbances in deep and shallow waters. In addition, the environmental conditions that limit safe navigation (maneuvering limit) are also discussed, while investigating the effect of the main engine output in particular. In both deep and shallow waters, a significant effect on the maneuvering limit is observed due to a reduction in engine output. Thus, the presented method is useful in capturing the maneuvering limit of the ship under external disturbances.