Composite prop trials

The world?s largest composite propeller, measuring 2.9m in diameter, has recently completed sea trials. QinetiQ, which undertook the trials on the Royal Naval vessel Triton, describes the outcome of the tests as successful, with a smooth take up of power and reduced vibration achieved.

While the tests were undertaken on a naval ship, QinetiQ believes a composite propeller has considerable potential for any sea-going application where weight is critical.

The propeller on Triton consists of five composite blades bolted and bonded to a Nickel-Aluminium-Bronze hub. The composite propeller, which is considerably lighter than a similar all Nickel-Aluminium-Bronze propeller, was fitted in place of a fixed pitch propeller during a regular docking period and sea trials took place in Falmouth Bay.

“The use of the lighter composite material meant that the blades could be thicker without significantly adding to the weight of the propeller,” explains Colin Podmore, project manager at QinetiQ. “Thicker blades offer the potential for improved cavitation performance so reducing vibration and underwater signatures.”

A data logging system was built into the propeller tail cone to collect outputs from strain gauges fitted to the blades and assess various loads. The data collected will help validate the mathematical models in the hydrodynamic and structural design programmes used in the propeller?s development. QinetiQ says the trials also helped it gather knowledge on the acoustic performance of a rotating composite structure and its impact on the galvanic environment at the aft end of a vessel.

The blades were manufactured by Dowty Propellers, while manufacture of the hub and propeller assembly were undertaken by Wärtsilä Propulsion.

QinetiQ says the development took on board some of the problems encountered during sea trials of a composite propeller developed under the auspices of the European project COMARPROP (Composite Marine Propulsion). This aimed to extend performance enhancements of composite propellers, achieve weight reductions of 50-70 per cent, increase overall fuel efficiency by up to 5 per cent and reduce hull/blade tip pressure fluctuations by up to 5dB. Aside from QinetiQ and Dowty, COMARPROP participants included Marintek from Norway, Cetena, Fincantieri RINa and the Consorzio Armatori per la Ricerca from Italy and the National Technical University of Athens from Greece.

“We learned from the COMARPROP experience and made some technical and design changes to our own composite propeller,” explains a QinetiQ spokesman.