Design and analysis of a carbon composite propeller for podded propulsion

Though the bulk of marine propellers are almost exclusively manufactured in metal alloys, there has been a recent trend to look into composite materials for propellers. Carbon fibre because of its extremely high strength and favourable strength-to-weight ratio is therefore a strong candidate as an alternate material for propellers. This paper investigates the design, analysis and basic strength aspects of a carbon composite propeller for application as a podded propulsion unit. Propellers are roto-dynamic machines and are prone to fatigue, and therefore, this is one of the important considerations in the choice of the material. Therefore, long-term study in terms of not only strength, hydrodynamic performance, but also fatigue properties must be well established if carbon composite propellers are to be used as substitute for the conventional propellers. This study presents the design of a propeller based on favourable stacking orientation of the multiple layers using unidirectional carbon fibre and epoxy resin, technique of manufacture and test results for hydrodynamic performance. For this purpose, the propeller conforms to standard NACA profiles for high efficiency. The study reports the analysis for strength on the basis of modelling the layer sequence and assigning the directional properties for the carbon fibre. To validate the results, a segmented loading frame has been designed and the deflections measured in the radial direction. The results help to verify the deflections obtained and therefore to confirm the analytical approach to obtain the dynamic stresses and the deflections. The study lays the foundation for redesigning the propeller making full advantage of the strength-to-weight ratio of carbon composite to obtain high efficiency and to obtain the hydro-elasticity-based response characteristic.