Development of an automated cable-laying system for DONET construction

This paper describes an automated cable-laying system that can automatically pay out a submarine cable on the seafloor while keeping balance with the ground speed. We have installed DONET (Dense Oceanfloor Network System for Earthquakes and Tsunamis) at Kumanonada and a ROV (Remotely Operated Vehicle) was successfully used to lay the cables which connect observatories to the nodes of the DONET. However, such a cable-laying work was regarded as one of the hardest works since it takes approximately 10 hours (about 10km distance) and is manually carried out by a ROV operator(s). The automated cable-laying system can contribute to reduce the physical and mental burdens on the ROV operator and speed up the construction of DONET2 (the second phase of DONET). In this paper, the components and cable-laying control strategies are described and some experimental results are presented. In addition, we report on the first mission to connect the borehole observatory C0002 to the Node D of the DONET. This achievement has made it possible to receive the data of the borehole observatory in real-time. The paid out cable is 8470m and the travelled distance is approximately 8000m.