# Toward More Sustainable River Transportation in Remote Regions of the Amazon, Brazil
## 2 Main Considerations to Improve the Efficiency of Boats  
There is no direct method to improve the efficiency of the small boats used for riverine transportation in remote regions. In fact, reducing the fuel consumption and increasing the performance of the boat requires several optimization projects since there are different fuel-optimal working conditions for each boat draft and speed [22].  
[PERSON] and [PERSON] [22] explained that there are several ways of decreasing the consumption of fuel by a vessel: reducing the required power for operation and propulsion; using fuel energy for propulsion and on-board equipment more efficiently; and using hybrid technologies for operation, combining fossil fuels with renewables, such as solar energy. According to [22], there are several factors to be considered to reduce the power required for propulsion, thus improving the performance of a ship. These can be classified into improving the propulsion system and reducing the boat's hydrodynamic resistance, as shown in Figure 1. To improve ship propulsion (Figure 1a), the propeller must operate optimally. Propulsion losses due to rotation of the shaft and propeller must be reduced, as must friction loads between the water and the propulsor, as well as those caused by the generation of tip and hub vortices. The propeller must operate in optimal wake conditions. In addition, the efficiency of the interactions between the components of the engine-shaftpropeller system must be maximized to increase the transmission of power delivered from the engine to the propeller.  
On the other hand, to reduce resistance (Figure 1b), reducing the size of the vessel and its speed may help; however, this practice does not seem to be economically viable for most applications. Other factors that may reduce a vessel's total resistance are: the resistance of the bare hull; the resistance of the waves generated when the bare hull is in motion; the resistance caused by appendages of the hull; the resistance caused by the seaway; the resistance caused by wind; and unexpected environmental conditions. In a practical way, it is possible to define the total resistance of a ship as the sum of frictional resistance (due to the friction of the fluid and the hull surface) and residuary resistance (due to the combination of viscous pressure and the wave-making resistance) [24; 49].  
[PERSON] et al. [24] describe how current attempts to decrease the hull resistance of vessels are related to speed, trim, added resistance in waves, bow shape, bulbous bows, stern shape, hull shape using CFD investigations, and air-bubble lubrication methods.  
As shown in Figure 1, increasing a vessel's sustainability by improving its performance involves several factors. [PERSON] and [PERSON] [32] explained that a reduction in fuel oil consumption of a vessel depends mainly on its type, speed, and working conditions. Therefore, in systematic studies, some parameters must be kept fixed for experimental and numerical investigations [50; 51; 52].  
A permanent long-term means of improving the performance of a vessel is to modify the shape of its hull to reduce resistance [37; 38; 39; 40; 26; 41], as this could yield a constant benefit. Therefore, following [PERSON] and [PERSON] [32], various means of modifying the forebody, midship, and aft body of the hull shapes of vessels can be considered, as shown in Figure 2. The possible gains that each of these modifications produces in reducing ship resistance can also be analyzed. Although these values are theoretical, they provide a preliminary idea about how permanent hull modifications can be useful. For instance, according to these data, gains of ~2-5% can be produced by optimization strategies applied to the forebody hull form.  
Figure 1: Factors that will reduce the power required for propulsion (**a**) by improving propulsion and (**b**) by reducing resistance. Adapted from [22].