Frequent attack of typhoon leads to crucial accidents caused by anchor dragging. In 2018, 21st typhoon hit west of Japan and the vessel, which was fallen into anchor dragging, collided with the bridge connecting Kansai International Airport and opposite shore. This accident had serious damage to the transportation of people and logistics. Moreover, when 15th typhoon in 2019, which gave crucial damages such as house damages and suspension of the electric power and the water supply, hit Chiba prefecture located in east of Japan, 107 vessels which were equivalent to one third of all vessels anchored in Tokyo Bay had the symptom of anchor dragging.

Seafarers must take measures as precaution to anchor dragging. However, missing its opportunity causes irreparable disasters. As the attack of typhoon becomes more frequent and serious, the means, which can evaluate the risk quantitatively to anchor dragging and help them make a decision, are necessary because seafarers have possibilities to fall into unexpected situation even if they are skilled and familiar with ship’s characteristics.

This study aims at detecting the signal of earlier stage of anchor dragging and visualizing the level of danger, as a mean to make a decision for taking precautions in an appropriate opportunity. With the acceleration meter, which can measure quantitatively ship’s lists and vibrations what human cannot recognize, acceleration data of ship’s motion were measured and evaluated. However, they don’t always show necessary factors for analyzing ship’s motion because they include all motions on the ship, such as wind, wave force and vibrations from its generator.

Then, the system, sorting of each range of frequency from measured accelerations and extracting necessary data, was created. This enables extraction of ship’s motion at anchor. The analysis results between the outer force affecting to the ship at anchor and the data extracted by this system, specified the signal of anchor dragging. In addition, the new system was built for indicating the risk of anchor dragging, by evaluating relationship between the signal of anchor dragging and the effect by outer force.

Measuring their data on actual ship showed the validity of this system. Thus, with measuring acceleration data at anchor and analyzing them, detecting ship’s motion, which indicates the signal of anchor dragging, proved to be possible.

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