This paper is the first half of the report on the study on microbubbles carried out by the SR239 project of the Shipbuilding Research Association of Japan, and describes the preparatory study for the full-scale experiment using a 116m-long ship. In the present study, first the skin friction reduction effect by microbubbles was investigated including the use of an array-of-holes plate for bubble generation, the effects of streamwise pressure gradient, surface curvature, and vertical plate, the sea-water effect, and the effect of bubble size. Bubble generators for the full-scale experiment were designed and built, and a preliminary injection experiment was carried out. Two new measuring devices for the full-scale experiment were developed; they are skin friction sensors and local void ratio sensors. Microbubble experiments were carried out in a 400m-long towing tank using a 50m-long flat plate ship, in order to obtain the scale effect data and to confirm the validity of the new devices for the full-scale experiment. The use of adhesives to fix measurement devices and cables on the hull surface was tested and established. The hydrodynamic fairing of the cables was also tested and established. Finally, a preliminary microbubble experiment using a small ship was carried out and the bubble behavior was observed.
