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November 15, 2005

Rolls Royce introduces Rim Drive thruster technology

The first commercial application of a new type of Rolls-Royce tunnel thruster launches a technology that could have a major impact on marine propulsion.Rim Drive Thruster

Rim Drive is a tightly integrated system combining electrical, mechanical and hydrodynamic elements.

The electrical motor takes the form of a thin ring. Its stator is incorporated in the tunnel and its rotor carries propeller blades that point inwards.

The first application is on an offshore support vessel, in the form of a type RT1600 tunnel thruster rated at 800 kW.

In due course the power range of rim tunnel thrusters will be broadened, and the technology will be used in other types of propulsor.

The electro-mechanical part of the technology will also be applicable to winches, steering systems and other products.

This technology has been developed in Norway over a period of several years by Rolls-Royce in Ulsteinvik and Smartmotor in Trondheim working in close collaboration.

A prototype unit has been subjected to function trials and long periods of endurance testing in Norway, and to detailed hydrodynamic evaluation in the cavitation tank at the Rolls-Royce hydrodynamic research centre in Sweden.

Several features combine to provide advantages for the owner, as R&T Project Manager Gunnar Johnsen explains.

"Water flow through the unit is unobstructed since there is no gearbox in the tunnel, nor are struts needed to support a hub. Propeller blades are attached to the rim, eliminating uncontrolled flow between blades and tunnel. The permanent magnet motor design is very efficient. Together these factors give a high total efficiency and reduced noise and vibration. Because more thrust is produced for a given power input, fuel consumption is reduced, and this saving can be substantial in applications such as offshore support vessels operating in dynamic positioning (DP) mode where thrusters may run for hundreds or thousands of hours a year. Fuel saving is not only a matter of money; the impact of the vessel on the environment is also reduced."

"The Rim Thruster is designed to be mountable and dismountable under water," continues Johnsen, "so that it can be removed for servicing if required without drydocking the vessel. We use water-lubricated bearings, eliminating propeller shaft seals and oil-filled gear housings."

"The motor is an integral part of the unit in the tunnel, so the ship designer no longer has to find space for a bulky electric motor in a thruster room," says Johnsen. "The only parts of the thruster inside the hull are the cables connecting it to the frequency control supply cabinet. The cabinet is similar to that used with any frequency controlled electrically driven thruster, and its location is flexible."

Olympic Shipping, based in Fosnavaag in Norway, has ordered the first RT1600 for a UT 712 CD anchor handler now under construction at Aker Yards Soviknes.

This vessel will have twin CP propellers for main propulsion, and other thrusters to give the station keeping power needed to meet IMO DP2 dynamic positioning standard.

The rim drive unit will be installed in the aft skeg acting as a stern side thruster.

"We are delighted that Olympic Shipping is fitting the new thruster type to their latest vessel," says Helge Gjerde, President-Offshore Propulsion in Rolls-Royce. " As equipment manufacturers we are dependent on forward thinking shipowners to bring new products and systems to market. Olympic's UT 712L is also the first to fit Rolls-Royce's newly developed DP2 dynamic positioning system, and also the equipment for making work on deck safer."

Bjorn Kvalsund, operations director of Olympic Shipping, makes the point that, "Our background in fishing and offshore has shown us that good equipment is the key to success, and that investment in technology that increases efficiency pays off in the long term. We aim to provide our oil company customers with vessels suited to their present and future needs, not their past ones, and to offer fuel efficient vessels with low environmental impact. The safety and well-being of our crews is just as important, and equipment that produces less noise and vibration is a valuable contribution to this."