An ROV developed for investigations of the sea bottom over a wide area can be operated both as a towed and a self-propulsive vehicle. Called DELTA, the shape is similar to that of a delta wing airplane. The vehicle has two-propellers and weight shift apparatus as actuators. The trim balance of DELTA can be achieved by weight shifting and direction is controlled by the thrust difference between the two propellers. The depth is altered by the trim angle and the forward speed, and course is adjusted by a direction control with the forward speed. The restoring torque caused by a combination of buoyancy and gravity force is expected to control roll. DELTA has roll, pitch and depth sensors to measure its attitudes, and position relative to the mother ship can be measured by an acoustic position sensor. Length of the vehicle is 1.13 m, displacement is 0.0525 m3 and weight in the air is 54.7 kg.


Many remote operated vehicles (ROV) have been developed for the maintenance and inspection of the ocean structure; most of these in practical use are self-propulsive with an umbilical cable. To exclude the effects of noise force from the cable a free swimming vehicle would be ideal, but most today are tethered so that the electric power can be supplied and control signals and obtained data can be transmitted. A self-propulsive ROV can be more accurately guided to an objective than a towed one. Consequently, a tethered selfpropulsive vehicle is usually used to inspect and maintain the ocean structure. In searches for a submerged airplane or ship or to survey mineral resources, efficiency over a wide area is important, and the towed vehicle is again advantageous from the viewpoint of its mobility and the convenience of operating it from the mother ship.

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