A Study on Risk Assessment for Anchor Dragging Using On-board Measurement Data of a Single Anchored Vessel

-Estimation of Holding Power change by VTDP-

Abstract

　A new risk assessment method for anchor dragging is proposed. Using several kinds of information that can be commonly obtained on the navigational bridge of ships, the touch down point of the anchor chain to the seabed is estimated based on the ship’s equations of motion. Firstly, accelerations and velocities of the ship are numerically evaluated using GPS data. Secondly, the hydrodynamic forces, such as added mass, damping force and wind force, are estimated based on the theory of ship maneuverability. Thirdly, the tension of the anchor chain is determined as a residual term of the equations of motion. Finally, the touch down point of the anchor chain to the seabed is estimated based on the catenary theory. In this study, the point is named as the Virtual Touch Down Point (VTDP) and used for estimation of the length of the anchor chain crawling on the seabed and its holding power.

　The new method was applied to the data set measured on an actual single anchored ship and the relationship between the chain length crawling on the seabed and the wind was investigated in the form of time series. The results show a negative correlation between them, suggesting the usefulness of VTDP. Therefore, it was confirmed that the method proposed in this study is effective for risk assessment of anchor dragging.