France’s Loiretech, a designer and manufacturer of tooling for large and complex thermoplastic and thermoset composite parts, has partnered with the French Defence Procurement Agency (DGA), Mecafrance and Naval Group in the Fabheli collaborative project to develop and commercialize a ship propeller molded from an epoxy carbon fiber thermoset composite. The aim was to develop and produce, on an industrial scale, a propeller with a reduced environmental footprint and lower energy consumption (around 15% lower).
|Composite ship propeller improves fuel economy, reduces noise levels.|
The project started in April 2016 with a digitization and calculation phase conducted by Mecafrance for the mechanical side and Naval Group for the hydrodynamic side, in order to dimension the carbon fiber composite propeller, which was twice as light as its metallic counterpart. The goal was to meet highly demanding specifications—the propeller is subject to significant mechanical loads when in use, so it was necessary to develop design concepts, production technologies and surface treatment to bear them.
A single-shot resin transfer molding (RTM) process is employed to mold the thick (up to 30 mm) epoxy composite blades individually. Three-part tooling with a moving core is used to accommodate blade foot undercuts. During processing there is three-bar of pressure at the mixing head, and the resin cures at 60°C. The blades are attached individually to an overmolded metal hub.
The composite design delivers numerous advantages according to Loiretech. For example, each of the five blades can be removed individually for maintenance. Further, the propeller is molded in a net shape without the need for post-process trimming and milling, which eliminates concerns regarding moisture ingress. In addition, tailing edge cavitation, and thereby noise levels, can be reduced through both the blade design and application of a special coating over the blades, while the flexibility of the blades results in hydrodynamic deformation contributes to improved fuel economy as well as less noise. Lower noise levels have positive implications in military applications.
Shipping company AML replaced a metal propeller on one of its ship with the new 1.1-meter-diameter composite propeller and conducted a sea trial conducted in March 2018 with the aim of subjecting it to high strain levels: numerous maneuvers at the ship’s maximum power made it possible to validate the intrinsic qualities of the composite propeller with the support of the Bureau Veritas certification agency. At the end of this trial, the propeller maintained a suitable appearance.
The project will now be continued to optimize propeller functionality and the manufacturing process with the objective of commercial production. Loiretech notes that while composite propellers are more expensive to manufacture in low volumes, they become affordable at production levels of 30–50 blades, and when added to the potential of enhancing fuel economy by 15%, commercial prospects look positive.