ClassNK has released the world's first guidelines on composite propellers covering the manufacturing process and product inspection.
The strength and corrosion resistance of composite materials makes them attractive for various applications, ships propellers included. A propeller made from carbon-fibre reinforced plastic (CFRP) weighs just 20% of a conventional one made from aluminium-bronze.
This weight reduction allows CFRP propeller shafts to be manufactured with smaller diameters, reducing costs. In addition, capitalising on the composite's strength, it is possible to produce thinner propellers with smaller blade areas, potentially increasing the propeller's efficiency.
For a marine setting, the material must have the required performance at least equal to existing aluminum-bronze composite materials, and it is necessary to confirm in advance that composite propellers can be manufactured with uniform quality.
In May 2014, ClassNK granted approval for the design and manufacturing process of the CFRP propeller. The propeller was developed with support from the ClassNK Joint R&D for Industry Program and marked the world's first installation of a CFRP propeller on a merchant vessel. Based on the knowledge gained in this project, the Japanese classification society formulated guidelines for assessing the manufacturing process and the post-manufacture testing/inspection regime.