# Research and Development of Inland Green and Smart Ship Technologies in China
## 3 Current Inland Green and Smart Ship Technology in China
### Inland Ship Technology
#### 3.1.1 Research and Development of Flat Ship Type with Full Form  
The depth of inland waterways is greatly affected by the season [20], so inland ships are generally designed to have variable draft. Based on the requirements of the cargo capacity, ships are generally wide and flat, with full bows and sterns, and relatively long parallel mid-hulls. Based on the most economical ship type parameters, the initial ship profile can be determined. The bow and stern profiles can then be optimized through numerical simulations and model tests to obtain a ship profile with minimal drag forces.  
_Bow type:_ A full-form ship with a shallow draft has a full-line shape, a large wet surface area, and a low Froude number [21]. The wave-making drag accounts for a small portion of the total drag such that the viscous drag accounts for the majority of the total [22]. Optimizing the bow line shape can effectively reduce the bow wave breaking drag and bilge-vortex drag. Bulbous, forward, watermelon, and vertical bows are the four bow types commonly used in inland ships, as shown in Figures 4-7. Commercial software FLUENT (2021 R2) was used to predict the drag at different speeds. The corresponding total drag coefficients are shown in Table 1. The bulbous and vertical bows exhibited similar drag performances. In areas with restricted dimensions, such as ship locks, the vertical bow has significant advantages and was therefore adopted in the inland ship types we developed.  
Total drag coefficient (\(C_{T}\)) in Table 1 is a dimensionless coefficient that represents the characteristics of total drag, which is defined as follows  
\[C_{T}=\frac{R_{T}}{\frac{1}{2\rho V^{2}S}} \tag{1}\]  
where \(R_{T}\) is the total drag; \(\rho\) is the density; \(V\) is the speed of ship; \(S\) is the wet surface area of hull.  
_Stern type:_ For wide, flat, and full-form ships navigating inland waterways, their sterns contract more drastically with a high longitudinal gradient. These shapes easily lead to bilge vortices at the tail [23], resulting in increases in energy dissipation and thus increases the drag on the ship. In addition, the large block coefficient of a stern body causes uneven wake at the surface of the propeller blades [23], which affects the propulsion efficiency. For the twin-skeg ship type, the twin stern fins act as a catamaran, thereby reducing the length-to-width ratio of the ship, and slowing the degree of stern hull contraction, thus resulting in superior performance. Twin-skeg ships use the deflection of the stern fins to pre-swirl the incoming flow, which can also improve the anti-rotating propulsion effect [24] of the propeller efficiency and demonstrate excellent maneuverability. The twin stern fins combine the excellent maneuverability of the twin-skeg ship type with good resistance to slamming, making it more suitable for river-sea-going vessels in both river and sea. Adopting an external rotating twin-skeg stern shape as shown in Figure 8, a pre-swirl is formed at the propeller disc during ship navigation to improve the propulsion efficiency of the propeller.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Vs (kn)** & **Bulbous Bow** & **Forward Bow** & **Watermelon Bow** & **Vertical Bow** \\ \hline
9.0 & 3.139 & 3.214 & 3.342 & 3.139 \\
10.0 & 3.156 & 3.260 & 3.363 & 3.125 \\
10.5 & 3.190 & 3.268 & 3.400 & 3.221 \\
11.0 & 3.256 & 3.339 & 3.517 & 3.322 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Calculation results of the total drag coefficient of different bow types.  
Figure 4: Bulbous bow calculation model.  
Figure 5: Rake forward calculation model.  
Figure 6: Watermelon head calculation model.  
Figure 7: Vertical head calculation model.