QinetiQ has successfully completed sea trials of the world’s largest composite propeller, which measures 2.9 metres in diameter and weighs significantly less than traditional Nickel Aluminium Bronze propellers.
Developed to explore the application of composite materials for marine propulsion, this is, according to QinetiQ, likely to have been the first time that a composite propeller of such a large size has been successfully demonstrated on a sea going vessel.
QinetiQ believes it has considerable potential for applications where weight is critical, such as with podded propulsion used by some marine vessels.
‘The use of the lighter composite material meant that the blades could be thicker without significantly adding to the weight of the propeller,’ said Project manager, Colin Podmore. ‘Thicker blades offer the potential for improved cavitation performance so reducing vibration and underwater signatures.’
Consisting of five composite blades bolted and bonded to a NAB hub, the propeller was designed to Navy standards, specifically to replace the fixed pitch propeller fitted to QinetiQ’s own trimaran warship prototype, RV Triton. The ship was launched in September 2000 and, at 90 metres in length with a beam of 22 metres, is the world’s largest motor powered triple-hull vessel.
The propeller was fitted to RV Triton during a routine docking period before undergoing an extensive programme of sea trials in Falmouth Bay. Unique data on loads exerted on the propeller blades was gained from a data logging system. This was built into the propeller tail cone and collected outputs from the strain gauges fitted to the blades.
According to QinetiQ, the information will be invaluable in validating the mathematical models in the hydrodynamic and structural design programmes used in the development of the propeller. Knowledge was also gained about the acoustic performance of a rotating composite structure and its impact on the galvanic environment at the aft end of a vessel.
Dowty Propellers, a part of Smiths Aerospace at Cheltenham, manufactured the composite propeller blades and Wartsila Propulsion in the Netherlands manufactured the NAB hub and assembled the propeller.