## 5 Conclusions  
This article explores the impact of ship towing speed, water depth, and flow velocity on the total resistance of 7000-t ships towing through a navigation tunnel with a width of 30 m using a 1:40 scale circulating water tank ship resistance test. It can provide key technical indicators for the development of towing equipment. Through this experimental study, the following conclusions were drawn:  
1. The impact of ship towing speed on the total resistance of ship navigation: Under the same conditions of water depth and flow velocity in the navigation tunnel, as the ship towing speed increases, the total resistance of ship navigation also increases. When the towing speed is between 0 m/s and 1.5 m/s, the change in total resistance of ship navigation is relatively small as the speed increases, with each level of towing speed increasing by about 50-300 kN; when the towing speed is greater than 1.5 m/s, the total resistance of ship navigation increases rapidly, with each level of towing speed increasing by about 100-560 kN.
2. The impact of the navigation tunnel's water depth on the total resistance of ship navigation: Under the same towing speed and water flow speed, as the water depth of the navigation tunnel increases, the total resistance of ship navigation decreases. When the water depth of the navigation tunnel is greater than 5.5 m, the total resistance of ship navigation changes slightly, which is 4-8 times the total resistance of the ship in still water; when the water depth of the navigation tunnel is less than 5.5 m, the impact of water depth on the total resistance of ship navigation is particularly evident, which is 5-13 times the total resistance of the ship in still water.
3. The impact of water flow velocity on the total resistance of ship navigation: When the water depth of the navigation tunnel and the towing speed are constant, the total resistance of ship navigation increases with the increase of water flow velocity. When the water flow velocity is 2 m/s and 2.5 m/s, the impact of water flow velocity on the total resistance of ship navigation is significant, and the total resistance is 1.5-2 times of the total resistance of ship navigation when the water flow velocity is 1.5 m/s.  
Figure 16: Analysis diagram of feasible range of drag resistance.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Traction (kN)** & **Towing Speed (m/s)** & **Velocity of Flow (m/s)** & **Water Depth (m)** \\ \hline
500 & 0–2.5 & 0 & \textgreater{}5.0 \\
800 & 0–1.0 & \textless{}1.5 & \textgreater{}5.0 \\
1000 & 0–0.5 & \textless{}2.0 & \textgreater{}5.5 \\ \hline \hline \end{tabular}
\end{table}
Table 12: Navigation suggestions.  
4. The results calculated by the existing resistance formula deviate significantly from the experimental values. The total resistance of ships in the towed navigation tunnel is 7-138 times the calculation results of the existing formula, among which the calculation value of the Zwankov formula is the closest to the experimental value, ranging from 7 to 30 times. Due to the increase in wave-making resistance or frictional resistance, the wave-making resistance coefficient or frictional resistance coefficient of the ship also needs to be adjusted accordingly.