More is less with new waterjets

Kamewa S3 waterjets claim a significant increase in efficiency, which translates into reduced fuel consumption for a given workload and consequently reduced CO2 emissions. At the same time there is a reduction in size, weight and life-cycle costs.

For most applications an S3 unit one size smaller than its predecessor will give the same performance. The result is a 25% reduction in the weight of the waterjet and its entrained water, together with a 12% smaller transom flange diameter. If the same frame size as before is specified, the Kamewa S3 offers a higher top speed. Alternatively there is either a larger payload, or less installed power and reduced fuel consumption, while maintaining the original speed.

These advantages for the customer are achieved through a variety of developments. At the heart of the waterjet is the mixed flow pump located aft of the transom flange. The impeller of the SII has been significantly improved, in particular its cavitation margin, by using the latest computational fluid dynamics (CFD) techniques combined with extensive testing in the cavitation tunnels at the Rolls-Royce Hydrodynamics Research Centre.

Optimising the whole pump unit and inlet duct gives a gain in propulsive efficiency of 2-3% compared with the already efficient SII series. An improved bearing design gives ideal running conditions for the shaft seal, reducing wear and tear, and provides close control of the clearance between the impeller and the pump housing, so maintaining the high pump efficiency over a long period.

The pump unit, nozzle and steering/reversing bucket are in stainless steel, and the bucket is now of a lighter but robust cast design incorporating an improved feedback system.

Kamewa S3 waterjets can be supplied as a steering and reversing units, or as simpler boosters giving ahead thrust only, enabling the ideal system to be configured for multi-jet installations or combinations of waterjets and CP propellers. As before, the inlet duct is fabricated by the shipyard to Rolls-Royce drawings and specifications, and the waterjets are optimised for the particular installation, covering a wide variety of vessel types and operating conditions.

A range of frame sizes is being introduced progressively, covering pump diameters from 50cm to 2m, and a power range from 2,000kW for the smallest S3-50 up to 40,000kW for the largest S3-200, the maximum power rating for very high speed vessels.

Waterjets are supplied with the latest developments in Rolls-Royce control systems, from the human/machine interface to hydraulic cylinders for steering and manoeuvring.