Study on Composite Material Marine Propellers

Abstract

In this study, the authors conducted mechanical property tests and the vibration characteristic tests of CFRP (carbon fiber reinforced plastics) specimens that can be adopted as new marine propeller materials. CFRP materials exhibited higher strength than NAB (nickel aluminum bronze casting) which is conventionally used as material for marine propellers. The damping ratio of CFRP materials was four times larger or more than that of NAB. In field tests using a small fishing boat, two types of CFRP propellers were manufactured by using CF-prepreg. One propeller was laminated with CF-Fabric and another with CF-UD, to obtain a quasi-isotropic composite. These are the so-called "built-up type" as three CFRP blades were assembled in an NAB boss. An NAB propeller of the so-called "mono-block type" was also manufactured to facilitate comparison with CFRP propellers. Analyses of field test results are ongoing. In vibration tests, the damping ratios of the both types of CFRP propellers were about ten times larger than that of the NAB propeller. Cavitation which can cause erosion on the surface is a severe problem for FRP propellers. Therefore, we cavitation erosion resistances for eight kinds of FRP and an NAB were evaluated in cavitation tests using a magnetostriction ultrasonic transducer. The cavitation erosion resistance of the NAB was much superior to that of FRP materials. However, it was found that aramid fibers on the surface of FRP can improve the erosion resistance. In order to improve the erosion resistance of FRP materials to the same level as that of NAB, the further research is necessary.