Azimuth thruster

　Out of the six azimuth thrusters on the CHIKYU, the two at the stern are of an always available fixed type, and the other four are thrusters of a type that can be stored on board ship and which can be hydraulically elevated and lowered. These six are all used at times of drilling, while depending on circumstances 2-6 thrusters are used when sailing. In the earthquake of March 11, 2011 one of these was damaged. The CHIKYU which was in Hachinohe Port at the time, and the stern was rubbed against the quay by the tsunami which was caused by the earthquake. This caused the massive weight of the ship to completely bear on the left thruster at the stern.

　“The azimuth thrusters do not only rotate the propellers, they also contain a slewing mechanism for turning the gearcase. A part called the swivel coupling, which is part of the slewing mechanism and connects the gearcase, broke off on this occasion, and use of the gearcase was lost.” Ishiwata tells how fortunately the propeller could be repaired and used, but the gearcase itself had been severely damaged and needed to be rebuilt. Because this is a one-off casting moreover, a mold needs to be built first once it has been ordered. The new azimuth thruster was mounted in June 2012, but that is the reason why it took over one year from it becoming unusable to mounting a new one.

　In the meantime the CHIKYU was forced to operate with the remaining five thrusters. “We could remain in one place, but it was difficult to remain in position in places where the current was strong, such as the Kuroshio along the Pacific western boundary.” This was one of the reasons that for a little over a year no surveys were carried out in the Kuroshio area, such as fault drilling in the Nankai Trough. “But once the six azimuth thrusters are complete, the CHIKYU will be able to display its powers as before,” told a delighted Ishiwata.