## 4 Result Discussion and Analysis  
### Comparative Analysis of Existing Drag Calculation Formulas and Experiments  
The Holtorp resistance estimation formula is derived through regression analysis and experimental data, relying on the geometric characteristics and various parameters of ships. For different types of ships and navigation conditions, these coefficients will vary [18; 19; 20; 21]. The Zwankov formula [22] is a method specifically used for calculating the resistance of inland river ships to water flow, and its accuracy is quite excellent at estimating the resistance of navigation in deep water. The resistance calculation formula for ships in restricted navigation channels obtained by [PERSON] et al. [11] has high accuracy when calculating the navigation resistance of ships of the 1000-t class in restricted Class III navigation channels by modifying the residual coefficient. [PERSON] [23] proposed an empirical formula for estimating the navigation resistance of a steel barge with a square coefficient of 0.748 and a weight of 60 tons, navigating in a channel with a water depth of 2.20 m and a speed range of 1.0-2.5 m/s. In the resistance calculation formula for barges in the Chuanjiang barge formula, the flow velocity at the bottom and sides of the ship increased significantly by 15% to 20% compared to the flow velocity in the navigation channel without the ship [12]. The formula for calculating the resistance of restricted navigation channels proposed by [PERSON] et al. [24] is applicable to barges of the 500-t or 1000-t classes. The applicable range of the resistance calculation formulas for each vessel is shown in Table 10.  
This experimental study is conducted in a navigable tunnel with a width of 30 m and a length of 960 m. The ship used in the study is a 7000-t class vessel, and the navigation method is to tow the ship with a small trolley. By comparing the parameters of the empirical resistance estimation formulas mentioned above with the parameters of this \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multirow{2}{*}{\begin{tabular}{c} **Zwankov and Chuanjiang** \\ **Barge Formula** \\ \end{tabular} } & \multirow{2}{*}{**[PERSON] Formula**} & \multirow{2}{*}{\begin{tabular}{c} **[PERSON]** \\ **Formula** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **[PERSON]** \\ **Formula** \\ \end{tabular} } & \multirow{2}{*}{**Navigation Tunnel**} \\ \hline B/b * & \(>\)8 & 3.42–6.42 & - & - & 1.39 \\ \hline h/T & 2–12 & 1.2–1.6 & 1.5–3.0 & - & 1.35–1.62 \\ \hline n & - & 4–12 & 4–10 & 5–50 & 1.9–2.3 \\ \hline Fr & - & 0.25–0.55 & 0.22–0.54 & - & 0.07–0.71 \\ \hline \multirow{2}{*}{tonage} & \multirow{2}{*}{500–1000-ton barge} & \multirow{2}{*}{\begin{tabular}{c} 1000-ton bulk \\ cargo ship \\ \end{tabular} } & \multirow{2}{*}{60-ton steel barge} & \multirow{2}{*}{500–1000 tons} & \multirow{2}{*}{7000 tons} \\ \cline{1-1} \cline{5-5}  & & & & & \\ \hline shape & natural channel & \
\begin{tabular}{c} trapezoidal and \\ rectangular channels \\ \end{tabular} & natural channel & canal &
\begin{tabular}{c} rectangular \\ waterway \\ \end{tabular} \\ \hline block coefficient & - & 0.8 & - & 0.89 and 0.95 & 0.84 \\ \hline \hline \end{tabular}  
* B/b is the ratio of channel width to ship width.  
\end{table} 
Table 10: Scope of Application of Resistance Calculation Formulas.