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 31m long research vessel Gunnerus, owned by the Norwegian University of Science and Technology (NTNU) Trondheim, since April 2015 and has clocked up 3000 hours of operation – 1500 on each unit.

Rolls-Royce Azimuth Permanent Magnet Thruster

Rolls-Royce Azimuth Permanent Magnet Thruster - Image courtesy: Rolls-Royce

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, said: “Station keeping and propulsion thrust response are better, maneuverability has improved and course stability is good. It’s a very impressive product.”

New Rolls-Royce Azimuth Permanent Magnet Thruster available

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.

The Azimuth Permanent Magnet Thruster is designed to be space saving and easy to install and maintain. The only components to be found in the thruster room are the slipring case, that transfers power to the thruster, the compact electric steering motors and a small lubrication swivel. With a submerged motor, no cooling equipment is required which saves further space and reduces installation cost.

Gunnar Johnsen, Rolls-Royce, Head of Electrical System R&T – Marine, said: “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.”

GUNNERUS - IMO 9371361

Research vessel GUNNERUS - Image courtesy: Trondheim Havn

The Azimuth Permanent Magnet Thruster is the latest in a range of Rolls-Royce propulsion and deck machinery products using permanent magnet technology. The first PM thruster application was installed on a test-bed vessel, the Olympic Octopus, in 2007 to 2009 and then commercially modified and re-installed in 2012. It has been operating for over 5000 hours without requiring maintenance.

From 2017 a new azipull AZP-PM model will be on offer – the AZP-PM 120 – rated at 1,800-3,500kW 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 900kW to 5,000kW and speeds up to 24 knots.

The new AZP-PM will have an L-drive configuration. It uses the same underwater unit as conventional azipull thruster but with a vertical shaft permanent magnet (PM) motor integrated into a new upper unit. A compact PM motor fits within the diameter of the mounting flange giving a small footprint and eliminating an upper gearbox. This avoids the complication of a coupling, foundations and motor for a conventional Z or C-drive.

Installation is simplified with the introduction the new weld-in tube hull fitting. This is a cylindrical steel element with a conical section to the mounting flange, which is easy to weld into the vessel’s hull structure, especially for a thruster inclined in all directions.

Three propeller types, controllable pitch, fixed pitch and fully feathering, will be offered for the AZP-PM, with the choice dependent on the vessel and its operation. All three types have been proven in use on existing azipull models.

Introducing the new AZP-PM, Gunnar Johnsen, Rolls-Royce, Head of Electrical System R&T – Marine, said: “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.”

Azipull thrusters with pulling propeller and streamlined underwater skeg have proved popular propulsion units since they were introduced in 2003. Over four hundred and fifty units have been manufactured to date with either direct mechanical transmission, or a separate electric motor.

Source: Rolls- Royce