Waterjet propulsion has been introduced for smaller vessels and workboats after three years of technical development to increase pump and steering efficiencies.
Rolls-Royce introduced its A5 Series of Kamewa waterjets at the International Workboat Show, in New Orleans, USA. These are designed for boats and craft up to 25 m in length, including workboats, motor yachts, smaller passenger vessels, pilot and patrol boats and other high-speed, shallow-draught vessels.
A5 Series is built from high-grade marine aluminium for low weight, and a more compact inboard footprint compared with steel-based waterjets, but without loss of thrust.
This series will eventually replace the FF range of existing waterjets, with size 29 set to be the first to be introduced. Eventually Rolls-Royce will offer seven sizes with power outputs between 100 kW and 1,230 kW.
Rolls-Royce general manager of waterjets Fredrik Appel said A5 was developed to improve performance compared to the steel series. “Overall pump efficiency is improved by 3%. Steering and reversing efficiency is improved by 8% and bollard pull is improved by 13%.”
“Besides the propulsion improvements, we have reworked the mechanical design to gain the benefits of a harmonised series,” Mr Appel explained. “We have adapted the design by reducing the space by 20%. However, we have also maintained an inlet waterway to accommodate the propulsion improvements.”
During its design, Rolls-Royce used computational fluid dynamics analysis and model scale testing at its own hydrodynamic research facility in Kristinehamn, Sweden. It incorporated elements from the S4 and S3/CA steel series of waterjets to improve performance.
“We have produced an axial flow waterjet that has a smaller footprint yet delivers improved steering and reversing efficiency, higher thrust at low to medium speeds and increased bollard pull performance,” Mr Appel explained.
He expects Kamewa A5 Series will provide best performance versus cost for vessels operating at speeds between 25 and 40 knots.
Rolls-Royce successfully carried out in-service trials of the new waterjet on board its own demonstration vessel, a crew transfer and harbour patrol vessel, operating in Kokkola, Finland.
Rolls-Royce has gained contracts this year to supply Kamewa waterjets for fast ferries, including two high-speed newbuildings that will be operated by Fred Olsen around the Canary Islands.