5.1 The effect of underwater fin configuration

　

 We investigate the sailing performance of the sail-assisted ship equipped with the underwater fin by using this simulation tool. The principal dimensions of the target ship used in this simulation are shown in Table 1. The outline of the sail-assisted ship is illustrated in Fig. 5. The 4 masts Position show in Fig.5. d1, d2, d3 and d4 is assumed 52.1m, 23.3m, -5.5m, -34.3m in according to the real cargo arrangements of general cargo ship. The sail is determined to be 2400 m² [1]. We have proposed the general cargo ship type as the sail-assisted ship. Since the speed of this ship is slow, it is thought that the gain of propulsive efficiency due to sailing is large. Since many this type ships has navigated in ocean, energy saving of this type ships seem to have great influence on the environment. The sails used in the sail-assisted ship are assumed to be rectangular soft sail and rigid wing sail. These sail systems achieve highly effective by combining the soft sail and rigid wing sail. This sail system is illustrated in Fig.6. Also the coordinate system of the sail is described in Fig.7. The aspect ratio of rectangular sail is fixed 2.63. The aerodynamics characteristic of sail systems is tested in wind tunnel [4]. The results of wind tunnel experiment are shown in Fig.8. The maximum lift coefficient can gain 2.6. The thrust due to wind in body fixed coordinate system is calculated from this experiment results. Simulation is used the maximum thrust coefficient for the relative attack angle. The coefficient of aerodynamics force and moment in motion equation is described as follows.

　

X'S = 4 × (CL sin(ΨW - β) - CD cos(ΨW - β))

Y'S = 4 × (CL cos(ΨW - β) - CD sin(ΨW - β))

N'S = (CL cos(ΨW - β) + CD sin(ΨW - β)) × (d1) + d2) + d3) + d4)

K'S = 4 × (CL cos(ΨW - β) - CD sin(ΨW - β)) × Hac

(8)