## 4 Result Discussion and Analysis
### Comparative Analysis of Drag Test Results  
To facilitate the analysis of the relationship between the total resistance of ship navigation and the Froude number Fr, the curves showing the variation of the total drag resistance of ships with Fr under different section coefficients are shown in Figures 10 and 11.  
As shown in Figure 10, with the increase of Fr, the total resistance change patterns of ships navigating in still water and in moving water are similar. As the cross-sectional coefficient of the navigation tunnel increases, that is, with the increase in water depth, the total resistance of ship navigation gradually decreases. As shown in Figure 11, when there is a flow velocity, the total resistance of ship navigation increases with the increase in flow velocity, and it is particularly obvious, which is 4-13 times the total resistance of the ship in still water.  
As shown in Figure 12, in the absence of current velocity, the resistance to the towing navigation of the ship is relatively small. Even at a towing speed of 2.5 m/s in a water depth of 5 m, the total resistance of the ship does not exceed 500 kN. As shown in Figure 13, when there is flow velocity, the resistance of the ship changes greatly, and even the maximum value can exceed 2500 kN. In this case, both the traction force of the equipment and the  
Figure 9: Measured total resistance and resistance calculated by various formulas in navigable tunnels. (**a**) Flow velocity 0 m\(\cdot\)s\({}^{-1}\); (**b**) Flow velocity 1.5 m\(\cdot\)s\({}^{-1}\); (**c**) Flow velocity 2.0 m\(\cdot\)s\({}^{-1}\); (**d**) Flow velocity 2.5 m\(\cdot\)s\({}^{-1}\).  
Figure 14 and 15 reveal a similar pattern in the variation of the total resistance to ship navigation with the change in the water depth-to-draft ratio (h/T) of the navigation tunnel. At the same towing speed, the total resistance to ship navigation decreases as h/T increases. When h/T is greater than 1.468, indicating a navigation tunnel depth greater than 5.5 m, the variation in total resistance to ship navigation with h/T is relatively small, ranging from four to eight times the resistance in calm water. Conversely, when h/T is less than 1.468, indicating a navigation tunnel depth less than 5.5 m, the total resistance to ship navigation curve shows a more significant decrease with the increase in h/T, ranging from 5 to 13 times the resistance in calm water. As the towing speed increases, the spacing between the two resistance peaks is larger than 1.468, indicating a navigation tunnel depth greater than 5.5 m. The variation in total resistance to ship navigation with h/T is relatively small, ranging from four to eight times the resistance in calm water. Conversely, when h/T is less than 1.468, indicating a navigation tunnel depth less than 5.5 m, the total resistance to ship navigation curve shows a more significant decrease with the increase in h/T, ranging from 5 to 13 times the resistance in calm water. As the to  
the curves of total resistance to ship navigation with varying h/T gradually widens. This indicates that the impact of the water depth-to-draft ratio of the navigation tunnel on the total resistance to ship navigation increases with the increase in towing speed.  
Based on the total resistance results obtained from the experiments, an analysis diagram, as shown in Figure 16, can be made. Considering factors such as safe towing navigation of ships in the navigation tunnel and complex flow conditions, navigation suggestions for towing navigation of 7000-t ships in a 30-m wide navigation tunnel are proposed, as shown in Table 12.  
Figure 14: Variation curve of total resistance of a moving ship in still water with h/T. v represents the towing speed.  
Figure 15: Curve of total resistance of moving water and ship with h/T. (**a**) Flow velocity 1.5 m\(\cdot\)s\({}^{-1}\); (**b**) Flow velocity 2.0 m\(\cdot\)s\({}^{-1}\); (**c**) Flow velocity 2.5 m\(\cdot\)s\({}^{-1}\).