1. Introduction
The 21’st century is an era of high oil prices. Companies are trying to maximize efficiency in response to with the everincreasing price of oil. Development is a key word for survival in this era when the shipbuilding is currently lagging behind as the technology being catched up by China. Currently, shipbuilders are investing heavily in manufacturing and designing parts that are maximized for efficiency. Considering as the efficiency, the company aims to gain an upper hand in competition among countries on the basis of high performance in comparison to price. Therefore, there is the problem which part can be increased on efficiency. Changing the design of the propeller is also one of the ways to increase the efficiency of ship. The propeller has had a great influence on human life, especially on ships and airplanes. As the history of ships has changed with the history of mankind, so has the propulsion method of ship. Representatively, Propeller has become the propulsion system of ship. There are many different types of propellers. In this study, the FPP (fixed pitch propeller) used in the majority of ships is investigated. Each of the fixedpitch propeller models of A, B and C were analyzed with the same material, inputting the same value for flow. Flow analyses are also carried out according to the number of these propeller blades. As the flow analysis result, model C is shown to be higher than the models of A and B on strength and efficiency^{[1~3]}. Currently, the number of propeller blades becomes three or four shapes which the shipbuilding company manufactures, while the latest technology involves using a propeller with a total of six wings by overlapping two threewinged propellers. In future, propeller models are expected to be more efficient due to the technological advance^{[4~12]}.
2. Analysis Results
2.1 Analysis models
In this study, ship propellers were modeled similar to actual features, and the number of wings was composed of three types, three, four and eight, respectively, as shown in Fig 1. 3D modeling used CATIA and was then interpreted using ANSYS. Table 1 shows the properties of structural steel, which is propeller material.
2.2 Structural analysis
2.2.1 Structural analysis conditions
Fig. 2 shows the analysis conditions at each model representatively. When the propeller is driven, the force of water is applied to the surface of the propeller. Therefore, the propeller centre was fixed as the supported face and a force of 10 N was applied in Z direction.
2.2.2 Structural analysis results
Fig. 3 shows the contours of equivalent stresses at models A, B and C.
At Fig. 3, the maximum equivalent stress values become 11.885 MPa, 9.9155MPa and 5.4244MPa at models A, B and C respectively. The maximum equivalent stress values of three models are made of the same material, but the equivalent stress values vary by depending on the geometry. The maximum equivalent stress of model A becomes more than two times by comparing with that of model C^{[13]}. Fig. 4 shows the contours of total deformations at models A, B and C. As shown by Fig. 4, three models appeared to have the largest deformation at the tip of the propeller's wing.
The values of the maximum total deformations become 0.15983 mm, 0.13251 mm and 0.063387 mm at models A, B and C, respectively. As the maximum equivalent stress value becomes, The maximum total deformation of model A becomes more than two times by comparing with that of model C. So, model C showed less overall maximum equivalent stress and less structural deformation than models A and B.
2.3 Flow analysis
2.3.1 Flow analysis conditions
Fig. 5 shows the flow zone of model 1representatively. In order to proceed with flow Analysis, the total length and diameter at each flow zone becomes 100 cm and 5 cm, respectively.
The flow velocity at inlet and the pressures at Boutlet are set as 8.5 m/s and 1 pa, respectively.
2.3.2 Flow analysis results
As flow analysis results, Figs. 6, 7 and 8 show velocity and pressure at the middle plane of flow at models 1, 2 and 3. Also, Figs. 6, 7 and 8 show the velocity and pressure of output and the plane section of wing at models 1, 2 and 3. As shown by Figs. 6, 7 and 8, the velocity at the inlet was same at models 1, 2 and 3. The flow velocities at the exit at models 1, 2 and 3 were 19.8449 m/s, 19.0107 m/s, and 24.812 m/s, respectively. It is shown that the speed of the exit increases with the increase in the number of blades. The flow velocity at inlet and the pressures at outlet are same at models A, B and C. The pressures at the exit at models 1, 2 and 3 were 18,595.9Pa, 65,606.1Pa and 173,294Pa, respectively, respectively. The results show that the pressure at the exit increases with the number of blades. So, the velocity and pressure of flow at the exit at model C become greater than models A and B ^{[14~15]}.
3. Conclusion
In this study, the propeller of any vessel was modelled by using CATIA like the actual shape. And the structural analysis and flow analysis were carried out with models 1, 2 and 3. So, the following results of this study were obtained:

In common, models A, B, and C all showed the most deformation at the tip of the propeller's wing. Model C showed less overall maximum equivalent stress and less structural deformation than models A and B.

the velocity and pressure of flow at the exit at model C become greater than models A and B.

Summarizing the results of this study, the arbitrary models are set as the same input pressure and velocity values as the number of wings increases. The number of wings is shown to be optimized as six.