Abstract: It is very important to reduce the ship's exhaust of carbon dioxide gas (CO2) that is assumed to be one of causes of global warming on environmental problems all over the world. Sailing ships are able to decrease the ship's exhaust gas rather than conventional ships with a diesel engine. Then, we had the research to investigate efficiency of an oceangoing sailing ship. The research consists of the investigation of aerodynamic characteristics on hybrid-sails and performance of a hull form on the sailing ship, and assessment of the sailing performance of the ship. In this paper, the aerodynamic characteristics of the hybrid-sails consisted of a rigid wing sail, a slat and a soft sail are shown. The aerodynamic characteristics of them are very important for the ship because the sails on the deck have large effect on the sailing performance. The experiments on various kinds of the sails were carried out at the wind tunnel. As a result, the hybrid-sails presented in this paper are very useful compared with the previous sails equipped on the deck of ships actually. The performance of the aerodynamic characteristics is also confirmed by calculated results of CFD.

　

 The environmental destruction according to global warming in the entire earth is worried about because a large amount of use of the fossil fuel increases CO2 in the atmosphere. In case of a ship, it will be effective to develop new technology on marine engines instead of the diesel engines in order to reduce exhaust gas. The thrust system using natural energy that might not make atmosphere dirty is also expected as the substitution of the diesel engines. It is examined to increase thrust by sails using the wind force in this paper.

　

 The idea on use of the wind as the thrust of motor ships had been already presented when the fuel price of a ship soared about 20 years ago in oil crisis. Square rigid sails were installed in ships and the effectiveness of the equipped sails was confirmed in Japan. For example, the sailing ships built about 20 years ago are shown in Fig.1 [1] and Fig.2 [2]. The tanker in Fig.1, which is 66m in Lpp, has two square rigid sails that the total sail area is 200m². The bulk carrier in Fig.2, which is 152m Lpp, also has two square rigid sails that the total sail area is 640m²

 Those sails are a circular arc form.

　

 Afterward, since the fuel price fell, the advantage of the equipped sails decreased in the higher cost of sail production, maintenance and operation. At present, the only one sail-equipped motor ship is plied in Japan except for small fishing vessels.

　

 In this time, high performance of the aerodynamic characteristics on the sail is expected rather than that of those square rigid sails shown in Fig. 1 and Fig. 2 in smaller costs. In our research institute, various investigations of the aerodynamic characteristics on the sails were carried out in the wind tunnel [3]. The results of the hybrid-sails, which has the seriously effect on the sailing performance of the ship, are shown in this paper. The sail consists of the rigid wing sail, which plays a role of a mast, a slat and a soft sail as in Fig.3. The efficiency of this kind of the sails has already shown by Nojiri et al [4]. Finally it is confirmed that CFD is efficient measures to assess the performance of these kinds of sails.

　

 A part of the results of the experiments in this paper has been used by Minami et al. [5] to assess the steady condition on sailing performance of an oceangoing sailing ship.

　

2. 1 Experimental models