At first, we check the steady characteristics of sailing performance. We investigate the balance condition and the change of the DHP for various wind direction when the wind velocity is constant. We compared the DHP of original hull with that of hull equipped with the underwater fin. We investigate the best fin arrangement for the sail-assisted ship from the viewpoint of economy using simulation model. The wind velocity is assumed to be 15.0m/s. The wind direction is changed from 0 degree to 180 degree

　

　

　

　

　

 with 10.0 degree interval. The ship speed and attitudes of ship for 3 different fin configurations are shown in Fig.9. The all estimation values of model equipped with the underwater fin are smaller than those of the original. We confirm that the underwater fin improve the sailing performance. Moreover the smallest deflection of leeway angle and rudder angle is Case 2. Case 2 is that fins are installed in center of the ship and two large sideboards. For Case 2, this large fin became resistance for leeway by viscous effect and cause large yaw moment due to fin. The rolling motion isn't influenced so much by the fin configurations. Perhaps the rolling moment due to the fin is guessed to be small for restoring moment around the x-axis.

 To confirm the change of propulsive efficiency due to underwater fin, the ratio of averaged DHP of ship equipped with the underwater fin and sail compare with the averaged DHP of ship equipped only sail in Fig. 10. This ratio is relative value for the DHP of the original hull without sail. Case 0 means the original hull equipped with only sail. The best efficiency is Case 3. Case 3 is that the underwater fin is installed in backside of ship and is smallest area in other configurations. The DHP of Case 3 decreases in 8.2% compared with that of original. Since the center of side force due to the sail is forward from midship, the fin position of Case 3 that is backward form midship can reduce the yaw moment generated by the sails. We have understood that the underwater fin located in the backside of ship decrease the yaw moment due to the sail. In addition, since the fin area of Case 3 is small, the added appendage resistance becomes small. The added appendage resistance of the underwater fin is thought to be bigger than the amount of the decreased resistance due to the improvement of sailing attitude. Also, we have found that the installation of the underwater fin in the back of hull is effective to reduce rudder deflection. However, the area of these fins is equivalent large when these fin are installed on real ship. It is understood that the fin should be located backward as possible. In the future, the method to store the fin in the hull should be considered when this ship is not sailing