Design Of Lightweight Marine Propellers Based On Numerical Methods

Bronze alloy is typically used to make marine propellers. It is hard, high yield strength and small bending deformation, but also has many weaknesses like inducing fatigue crack easily, serious cavitation, poor vibration performance and high weight. With the development of new materials, it is possible to design new lightweight propellers in recent years. For instance, the aluminum alloy is low weight, good corrosion resistance, easy forming, excellent weld ability and no low temperature brittleness, etc.In this thesis, a combination of Lifting Surface Method (LSM) and Finite Element Method (FEM) will be available to calculate the performance and strength of a marine propeller. Firstly, the hydrodynamic performance of a propeller is verified, based on the LSM. Also, the strength of its blades is also checked by the FEM. Then the influence of the hydrodynamic performance and the strength by changing its thickness is analyzed, so that we get the lightweight material propellers which also meet the requirements for original design.We take a real propeller of a 46 meter semi-planing boat for example to calculate its hydrodynamic performance. The relative errors of thrust and torque coefficients are both less than 6%. Besides, increasing the thickness of the propeller will diminish the thrust and torque coefficients a little and improve its cavitation performance obviously. While if decreasing, the thrust and torque coefficients would be a little bigger than the values of original thickness, the cavitation performance would become worsening.We take two propellers of different diameters for examples to analyze the strength. The results show that the stress of a bronze alloy propeller with 30% thickness increased can meet the allowable stress of the aluminum alloy.At last, with calculating, analyzing, we obtain an aluminum alloy propeller and a carbon fiber composites propeller respectively. Compared with the bronze alloy propeller, the weight of the first one loses up to 158.3kg, loss ratio is 59.2%. The other one's loses up to 207kg, loss ratio is 77.4%. So the purpose of losing propellers'weight comes true, which also gives a reference method for designing lightweight propellers.