New CPP from Rolls-Royce

Computational fluid dynamics (CFD) and cavitation testing were used to refine the contours of the propeller hub and blade roots.

The new Kamewa CP-A hub for controllable pitch propellers (CPP) has been developed from the established XF-5 design. While hubs for CPPs are mature products, the company is claiming that it has been possible to improve the power to weight ratio by about 20 percent without compromising its strength, with the added benefit of greater wearing surfaces for the blade bearings.

The operating principle of the XF-5 hub has been retained: the arrangement in which the pitch of the blades is set by a hydraulic piston connected to a crosshead in the hub, which carries slide blocks riding on pins in the blade feet. Actuating oil is fed along twin tubes through the hollow-bored propeller shaft. A feedback mechanism ensures that the ordered blade pitch is achieved and the system gives full control of propeller pitch, providing ahead, neutral and astern thrust steplessly. A fully feathering version is also available. An associated low pressure oil system lubricates the hub mechanism and the bearing surfaces at the root of the blades. Seals at each blade foot prevent leakage of oil out, or sea water in, and the hub is maintained at a slight over-pressure. The new hub is being offered in two main versions. The CP-A standard covers speeds up to about 30 knots and the CP-A/H is intended for faster vessels. They are suitable for the full range of applications, both commercial and naval, and the new hub will be offered in a wide range of sizes, covering powers above about 500kW with no defined upper limit.