## 3 Results and Discussion
### Response Surface Results Analysis  
To further analyze how each factor affects the real ship power, the response graph based on two independent factors is shown in Figure 6 below. Figure 6a shows the response surface of the actual ship power when the ship model speed and displacement interact if the ship attachment value is 0.5. When the initial displacement is 0.36 t, the corresponding real ship power increases from 3.12 kW to 272.3 kW if the ship model speed increases from 0.44 m/s to 2.06 m/s. When the displacement is 0.41 t, the actual ship power increases from 5.56 kW to 288.42 kW. It can be seen that the increase in displacement will lead to the increase in real ship power under the same speed condition. When the speed is 0.44 m/s, the real ship power increases from 3.12 kW to 5.56 kW with the increase in displacement (from 0.36 t to 0.41 t). The corresponding real ship power is increased from 272.3 kW to 288.42 kW when the model speed is 2.06 m/s. The data analysis results show that the speed has a more obvious impact on the real ship power compared with the displacement. The higher the speed, the more obvious the increase in the actual ship power, which means the higher the power requirements of the ship. But, the change in displacement has no significant impact on the real ship power.  
Figure 5: (a) Analysis of normality. (b) Comparison of predicted and measured values.  
Figure 6: \(Cont.\)  
Figure 6b shows the coupling effects of ship appendages and speed on actual ship power when the displacement is 0.385 t. When the vessel is not equipped with appendages, the increase in ship model speed from 0.44 m/s to 2.06 m/s results in an increase in actual ship power from 3.2 kW to 280.81 kW. When the ship is equipped with all of the appendages, the corresponding actual ship power increases from 4.28 kW to 283.83 kW. When the speed is 0.44 m/s, the ship is equipped with no appendages to all appendages, which increases the actual ship power from 3.2 kW to 4.28 kW. When the speed is 2.06 m/s, the corresponding actual ship power increases from 280.81 kW to 283.83 kW. It can be seen from the data results that the speed is significantly greater than the ship appendages in terms of the influence degree on the actual ship power. In the selection of ship power equipment, speed is still a very important reference factor. In contrast, changes in ship appendages do not cause large fluctuations in actual ship power.  
Figure 6c shows the coupling effects of ship appendages and displacement on actual ship power when the ship model speed is 1.25 m/s. When the vessel is not equipped with an appendage, an increase in displacement from 0.36 t to 0.41 t results in an increase in actual ship power from 73.52 kW to 82.17 kW. When the ship is equipped with full appendages, the corresponding actual ship power increases from 73.63 kW to 85.52 kW. If the displacement is 0.36 t, the ship is equipped with no appendages to all appendages, which increases the actual ship power from 73.52 kW to 73.63 kW. If the displacement is 0.41 t, the corresponding actual ship power increases from 82.17 kW to 85.52 kW. The analysis of the data results shows that the increase in ship appendages and the change in displacement do not lead to a large fluctuation in the actual ship power. With the increase of the two, the real ship power shows a slow change trend. The conclusion shows that appendages and displacement are the secondary factors of power equipment selection. But, the influence of displacement on the power weight of an actual ship is greater than that of appendages.