Military and civilian markets generally have different requirements when they commission products made from composite materials. But the French consortium FABHELI had to meet the needs of both groups when producing a 2.9-foot, CFRP propeller prototype. It succeeded in developing a propeller that has the potential to decrease ships’ energy consumption and maintenance costs, improve their hydrodynamic efficiency and cut their acoustic emissions. Plus, the propellers could be manufactured at a price that would appeal to both military and civilian shipbuilders.
FABHELI comes from “fabriqué,” short for fabricated, and “heli,” the French word for propeller. Loiretech, a designer and manufacturer of composite tooling, leads the consortium. Its partners include NAVAL Group, a designer/builder of naval submarines and surface ships, and Méca, which makes innovative composite structures. Subcontractors included Bureau Veritas, a provider of testing, inspection and certification services, and the AML shipyard, which supplied the test vessel for the new propeller.
In this two-year project, the consortium demonstrated several advantages of composite propellers over metallic ones. One was fuel savings, which is important both to military customers and to civilian markets. Fishermen, for example, spend 80 percent of the money they make on each trip for fuel.
To develop an efficient design, the consortium used adaptive profile computing to calculate and then test, using simulations, the effects of the flow of water (hydrodynamic behavior) and the rotation of the blades on various propeller designs.
There are three major components to the blade. “The leading edge is very important, because it has to separate the flow of water,” says Franck Bourcier, Loiretech’s vice president of marketing and innovations. “The second thing is the surface of the blade, because you must always have contact between the blade and the water. If you lose contact at certain moments, you lose accuracy, which is what we are looking for. You must also have a very thin trailing edge to avoid cavitation; the thinner the trailing edge, the better the result will be and the more efficient the blade will be.” (Cavitation is the development of bubbles in liquid caused by the movement of the propeller.)
The military was particularly interested in the composite propeller’s potential to reduce cavitation and thus acoustic emissions, which would make it harder for an enemy to track a ship using sonar. A proprietary coating on the blade helped dampen this noise as well.