Azipull thrusters with pulling propeller and streamlined underwater skeg have proved popular propulsion units since they were introduced in 2003 (photo: Rolls-Royce)

Rolls-Royce has successfully completed a year of sea trials of its new Azimuth Permanent Magnet Thruster and is making it available to customers for the first time at this year’s SMM.

The thruster has been in operation aboard the 31-metre long research vessel Gunnerus, owned by the Norwegian University of Science and Technology (NTNU)Trondheim, since April 2015 and has clocked up 3,000 hours of operation – 1,500 on each unit.

On installation aboard the Gunnerus, the vessel’s existing shaftlines and rudders were converted to PM azimuth thrusters but the existing generator sets were maintained. This allowed exact comparisons to be made of performance before and after installation.

Over the course of the trial researchers found a very high motor efficiency, 97% at nominal speed and very high over the whole load range, an increase in bollard pull (+20%) and speed – approximately one knot over the range for the same input power – with airborne and structural noise readings lower or similar to previous performance. Hydro acoustic noise was improved.

Reflecting on the vessel’s performance, the Gunnerus’ Captain, Arve Knudsen, says, “Station keeping and propulsion thrust response are better, maneuverability has improved and course stability is good. It’s a very impressive product.”

The PM Thruster has fewer moving parts than conventional thrusters. It combines a ring-type permanent magnet electric motor, propeller and nozzle in a tightly integrated propulsion unit. Simple bearings in the rotor hub carry all loads, and only a small oil circulation pump is required. This system carries less oil than conventional thrusters reducing the risk of environmental damage if spilled. The system uses biodegradable oil, which has the Vessel General Permit (VGP) for Environmental Acceptable Lubrications (EAL) approval.

Gunnar Johnsen, Rolls-Royce, Head of Electrical System R&T – Marine, says, “Tests of the new Rolls-Royce Azimuth Permanent Magnet Thruster prove it can meet customer demand for a highly efficient, reliable and sustainable thruster with low noise and vibration which is easy to install and service. We expect to see a reduction of 50% on the maintenance costs and in case of any maintenance, our condition based monitoring system shows you the current health of the units and allows you to plan maintenance ahead.”

From 2017 a new azipull AZP-PM model will be on offer – the AZP-PM 120 – rated at 1,800-3,500 kW continuous. This will be followed by two smaller frame sizes, 085 and 100, and one larger, the 150. They will be available for powers from 900 to 5,000 kW and speeds up to 24 knots.

Introducing the new AZP-PM, Gunnar Johnsen, Rolls-Royce, Head of Electrical System R&T – Marine, says, “The PM motor provides a very high efficiency over a wide speed range and reduces the space required in the thruster room. The propulsion system is well qualified for ships with ice class demand. Combined with the proven high propulsive and hydrodynamic efficiency of the azipull, this will be a winning combination.”

Tags: Rolls-Royce