Analysis of number propeller blades on traditional boats 3 GT capacity with engine rotation speed variation

Limited range of fishing areas is one form of loss experienced by fishermen in Indonesia, especially fishermen who still use traditional boats 3 GT capacity. The driving component of one of the problems, one of which is a propeller. Propeller commonly used by fishermen still uses 3 blades propeller with less than maximum thrust distribution and fluid velocity. The purpose of this study is to optimize the number of propeller blades in traditional boats 3 GT capacity with variations in the number of propeller blades 2,3 and 4 and rotational speed of 700 RPM, 1200 RPM, 1700 RPM, and 2200 RPM. The method used to determine the amount of thrust and fluid velocity through CFD simulations. Flow simulation results show the maximum thrust obtained at 1700 RPM rotational and the maximum fluid velocity obtained at 2200 RPM with a pressure of 15.3Mpa and a fluid speed of 3340.16 m/s on a propeller of 2 blades. Whereas the minimum thrust force is obtained at 700 RPM rotational with pressure 0.21Mpa in propeller with 3 blades and the minimum fluid speed is obtained at 700 RPM rotational with a fluid speed 369.33 m/s on propeller with 4 blades.


Introduction
The limited range of fishing grounds is an obstacle for fishermen who use traditional boats 3 GT capacity. The lack of sea catch results, resulting in losses for the fishermen who cannot compensate for the market price with the amount of catch that is obtained. Factors that influence these problems are due to lack of power generated from the ship's propulsion system. The ship propulsion system consists of an engine and propeller. The consequences received by fishermen so as not to experience a large loss one of them by modifying the propeller drive. Propeller is one part of the engine that functions as a mechanical drive, for example on airplanes, ships, hovercraft and others [1]. Optimization of the number of blades on the propeller is very influential on the performance of the boat, especially to increase the thrust and speed of the boat and suction power. However, as the number of blades increases, the suction cavity level tends to decrease [2]. The purpose of this study is to determine the most optimal number of blades used in the traditional boat 3 GT capacity with a variation of blades totaling 2.3 and 4 at 2200 RPM, 1700 RPM, 1200 RPM, and 700 RPM rotations.

Traditional boats 3GT capacity specifications
The traditional boat 3GT capacity specifications which are carried out in this study, have parameters as a reference in the process of determining the calculation of the resistance of a boat or vessel to be used   Figure 1 shows the dimensions of the outer diameter of the propeller of 198 mm, with a thickness of the propeller blade of 1.67 mm. and then the magnitude of the skew angle at above geometry fix pitch propeller of 3.74 degrees and the magnitude of the rake angle on the propeller of 9.97 degrees. For determine the magnitude of the skew angle with measured at the shaft center line, in the projected plane, which can be drawn between lines passing from the shaft center line through the mid chord position of any two sections, so that it determine of the rake angle with between a calculation generator line rake (iG) and skew-induced rake (iS) [2].

Material
Fix pitch propeller material used in traditional boat 3 GT capacity uses Aluminum Alloy material with the following chemical composition [5]:  [6]. Then to determine the magnitude of seawater pressure, the following equation is obtained [7]: (1) From the equation above we get the seawater pressure of 5022.5 Pa (502.25Kgf/m 2 ), the pressure will be used as a propeller domain parameter in the simulation process.   Figure 2 shows the environmental conditions that occur in propeller traditional boat 3 GT capacity. The environment condition is influenced by the speed of seawater currents of 4 m / s [11], with sea surface temperatures around 29 0 C [12]. As well as the hydrostatic pressure and vessel pressure conditions of 602.7Kgf/m 2 with a maximum propeller rotation of 2200 RPM [4], through a CFD simulation in the processing of using SolidWorks software.

Max pressure and max velocity of propeller charts
The charts below shows the comparison between max pressure and max velocity on traditional 3 GT capacity boat propellers based on variations in rotational speed.  The charts on figure 7, shows that the velocity of fluid produced by the propeller from each number of blades has a significant increase in each rotation, while the pressure generated at the propeller each number of blades has a less consistent increase.

Conclusion
The results of research on optimizing the number of propeller blades on traditional boats using 3GT using CFD (Computational Fluid Dynamic) in Flow Simulation, show the most optimal results based on the propeller number of 2 blades with maximum pressure results of 1530440.05Kgf/m 2 or 15.3 MPa with required loading 1700 RPM under environmental conditions with pressure of 602.7Kgf/m 2 and seawater flow velocity of 4 m/s. While the most optimal fluid velocity is the propeller of 2 blades with a maximum speed of 3340.16 m/s at 2200 RPM loading with the same environmental conditions.