Mooring motions works wrong on ocean measurements such as acoustical position fixing, ocean acoustical tomography, and so on. Therefore, acoustical measurements of mooring motions are required to obtain good accuracy on above acoustical ocean measurements. In this paper, a drag coefficient of chained glass balls to get a buoyancy force of a mooring system is determined on the basis of experimental data in the sea. Mooring motions in ocean currents are examined with the lumped mass method by using its drag coefficient and other dynamical parameters. A motion of taut mooring, such as the ratio of the mooring line length to the water depth is small, draws a circle in a rotating current, on the other hand it draws a track like a numeral of 8 in an elliptically rotating current. It is confirmed that its motions were capable to be estimated from current velocities by using a kind of simple dynamical equivalent model. This makes easier to measure mooring motions than the acoustical method. A sea test for acoustic ranging was conducted. It is confirmed to increase the accuracy of acoustic ranging by the correction of them using transceiver displacements estimated from current velocities.

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A high resolution magnetic anomaly map of the northern part of the Sado Ridge can reveal buried structures in detail from seaborne magnetic data. A magnetic boundary map was obtained from the maxima of horizontal gradients of magnetic total intensities, and it was compared with another boundary map obtained from three component anomalies measured by the shipboard three component magnetometer. Moreover, apparent magnetization intensities were also calculated. High intensity areas indicate some volcanic intrusions, and they are located around the edge of gravity basement high and low areas.

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