This paper describes the concept of the buoyancy-control type ballast-free ship proposed by Yokohama National University and the result of various studies carried out to examine its performance. In this study, we carried out model experiments in a water circulating channel to measure the ability of the system to exchange seawater in the buoyancy control tanks. We also confirmed by numerical analysis that the increase of the ship resistance by the appendage, i.e., intake and exit vents, is less

more »

... han 1 percent of the total ship resistance. One of the aims of this concept is to alter existing ships to ballast-free ones by leaving the structures of the existing ships almost as they are, i.e., ballast tanks of conventional ships are to be used as buoyancy control tanks necessary for the proposed system with slight modifications. In order to realize retrofitting of conventional ships to ballast-free ships easily, we propose a simple method by inserting intake and exit units into the space between longitudinal stiffeners on the ship bottom. Furthermore, structural analysis by using a finite element method was performed and we confirmed that no serious problem occurs by the buoyancy control operation. The proposed ballast-free ship concept is a favorable option to solve the ship's ballast water problem.