Possibility of Tacking Maneuver Operation of Japanese Traditional Sailing Trader "Bezai-ship"

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"Bezai-ship" is a type of typical Japanese sailing trader in the 18th to the mid-19th century. The rig is simple ; single mast with a huge square sail named "Bezai-ho." The sailing traders are required to have good maneuverability for tacking and wearing operation. However, it has not been revealed that the Bezai-ship could perform the tacking operation. This research aims to investigate the possibility of tacking operation of Bezai-ship by means of numerical simulation. On the other hand, until early-20th century, many Bezai-ships were used with Chinese lug rig, "Shinshi-bo" in Japanese, instead of Bezai-ho. Therefore the tacking performance in this case was also investigated.Aerodynamic performance of the Bezai-ho and Shinshi-bo were studied by means of wind tunnel tests, sea trials and numerical calculations. A sail dynamometer boat Fujin was employed for the sea trials, by which the aerodynamic forces acting on the sail and sail shapes were measured at the same time. Using the measured sail shapes, sail forces were calculated by means of a vortex lattice method.At first, the results of numerical simulation of her wearing operation were compared with the measured data, which were obtained by the sea trial of the reconstructed Bezai-ship Naniwa-maru. The numerical simulation calculates ship response to the measured rudder angle, and shows the ship trajectory and the sailing state parameters. The calculated results coincided well with the measured data.Then, the numerical simulation of tacking operation was performed. The simulated results showed the difficulty of tacking operation of this ship with the Bezai-ho. However, when the Bezai-ship was rigged with Shinshi-bo instead of Bezai-ho, the simulation showed that the ship could perform tacking operation easily. Therefore it can be concluded that the performance of the hull of Bezai-ship could stand comparison with the Western tall ships of those days.