Azimuthing Permanent Magnet Thruster

Marine

NEW Azimuthing permanent magnet thruster

1 Propulsion Azimuthing permanent magnet thruster (AZ-PM)

AZ-PM combines a ring-type permanent magnet electric motor, propeller and nozzle in a tightly integrated propulsion unit. It offers improved efficiency and simplicity compared to conventional geared azimuth thrusters with separate electric motors in the thruster room.

The rotor of the motor forming a ring around the propeller blades combined with advanced blade shapes, suppresses or eliminates cavitation. The motor stator is incorporated in the nozzle which controls water flow and provides increased thrust over a wide speed range. The underwater unit can be rotated in azimuth to give steering and vectored thrust in any direction. A steel structure carries the steering bearing and this is simply bolted into the hull. Only limited footprint space and headroom is required in the thruster room as the only components there are the slipring case that transfers power to the thruster and the compact electric steering motors. Speed control is by varying the frequency of the voltage supplied to the thruster motor. A very high motor efficiency, 97% at nominal speed and high efficiency over the whole load range, and the submerged motor mean that no cooling equipment is required, saving space and reducing installation cost. Simple bearings in the rotor hub carry all loads, and only a small oil circulation pump is required.

AZ-PM benefits: • Reduced hull space demand Typical applications: • Improved propulsion efficiency • No inboard cooling system • Construction vessels • Improved fuel efficiency • No hydraulic pumps or powerpacks • Ferries • Reduced noise and vibration, • Environmentally friendly • Wind turbine support both airborne and structural • Less maintenance on board vessels • Reduced hydro acoustic noise • Reduced maintenance at docking intervals • Towing and workboats • Reduced or no cavitation • Reduced steering gear torque • etc. • Uses EAL (environmentaly acceptable oil) • Equipped for condition monitoring with reduced volume

2 PM technology

The AZ-PM thruster is the latest in a range of Rolls-Royce propulsion products using its permanent magnet technology.

This technology is based on electric drive where the motor is in the form of a ring round the propeller. The moving part of the ring is a rim around the propeller blades which carries a series of strong permanent magnets. The rotor, fitted within a series of magnets, turns within an outer ring which form the stator. When current is supplied to the motor from the variable frequency power supply the electromagnets are excited in a particular sequence and the resulting magnetic fields interact with the 1 field from the rotor magnets creating a torque that turns the rotor and its propeller blades. At the centre of the thruster the propeller blades are joined to a hub, which has two functions; to carry the bearings taking propeller thrust and provide radial location of the rotor, and to improve the hydro-dynamic efficiency of the thruster. Loads are transferred to the stator through struts. Both rotor and stator are sealed against water ingress and operate fully submerged.

Rolls-Royce PM technology is flexible, and is currently applied in this integrated propeller drive form to tunnel thrusters (TT-PM) and azimuth thrusters (AZ-PM). Other versions in which the PM rotor is arranged to turn an output shaft provide a high torque, low speed, drive for winches.

Among the advantages of this PM thruster technology are high efficiency (at nominal speed) over the entire speed range, leading 2 to low thermal losses and eliminating the need for separate cooling systems of the submerged motor. Thrusters are compact 1. Permanent magnetic tunnel thruster (TT-PM) and robust, and require less space within the hull. They are 2. The electric motor forms a thin ring around the propeller. simple, with far fewer components than geared thrusters and No gears, and motor inside the hull. are also quieter, with reduced structure and airborne noise.

Speed control of the monoblock fixed pitch propeller is by varying the electric supply frequency using an Active Front End system or 12-pulse converter.

3 Propulsion Development and verification

Rolls-Royce has invested heavily in research, development and verification programmes to ensure that the existing and future PM thruster products are robust, efficient and reliable, also meeting customers’ wishes for ease of installation and servicing.

Around the millennium PM technical possibilities were explored and calculations made, resulting in a 50kW tunnel thruster whose physical proportions were chosen to give answers on the electrical side that would apply to larger units. This unit was run for long periods in a water tank. The results were encouraging enough for a full size 800kW technology demonstrator to be designed, built and installed as a stern tunnel thruster on the offshore anchorhandler Olympic Octopus for evaluation under real conditions including much time in dynamic positioning (DP) mode. Performance and efficiency were good, but it was concluded that water lubricated peripheral bearings had marginal durability in demanding worldwide service and long term DP operation. The propeller already had a hub for good hydrodynamic reasons so it was decided to use bearings in this hub on a static shaft supported by stream- lined stays, simple and effective. In 2011 the first TT-PM 1600 tunnel thruster was manufactured and began a six month test programme A TT-PM 1600 tunnel thruster was installed in Olympic Octopus in 2012. in a quayside rig. At the same time installation details were final- ised for flexible mounting in the tunnel and underwater exchange Two AZ-PM technology demonstrators were manufactured for a and in 2012 the unit was fitted to Olympic Octopus. long term evaluation programme on the research ship Gunnerus.

The TT-PM 1600 and larger TT-PM 2000 were launched as Gunnerus is owned and operated by NTNU, the Norwegian commercial products in 2012. In parallel with PM thrusters, shaft University of Science and Technology based in Trondheim. The drive high torque PM motors were developed for powering winches. 31.25m long vessel is equipped to carry out research in the fields of biology, technology, geology, archeology, oceanography and Much of the technology and experience transfers to the new PM fisheries, and as such is an asset to many of the courses offered by azimuth thruster, the main developments being in integrating the NTNU. When the ship was conceived the aim was that it should not motor stator into an efficient nozzle and designing an advanced only be a platform from which scientific research could be carried propeller with maximum resistance to cavitation. out, but also be itself a tool for the development of innovative marine technology. This role Gunnerus undertakes in the thruster As with all the Rolls-Royce propulsion products the latest electrical development work. and mechanical design methods have been used to the full, with extensive CFD studies to maximise hydrodynamic efficiency.

PM tunnel thruster 2013 PM azimuthing thruster 2015 PM azimuthing pulling thruster 6600 running houres 3000 running houres to be launched in 2017

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Developement & verification

GunnerusAs built, the is ship owned had diesel and electricoperated propulsion in a traditional twin byscrew NTNU, and therudders Norwegian arrangement. University The original high speed diesel ofgensets Science are and retained, Technology and these based are fitted in with extremely flexible Trondheim.mountings to The stop 31.25m any structure-borne long vessel noiseis potentially affecting equippedresearch results. to carry As part out of research the conversion in the work the propellers, fieldsshaftlines of ruddersbiology, andtechnology, steering gear geology, were removed, and the archeology,sterntubes plugged, oceanography but the skeg and remains fisher -in place and the ies,afterbody and as was such modified is an asset to take to the many PM azimuth of thrusters. theThese courses technology offered demonstrator by NTNU. PM azimuthWhen thrusters have a therating ship of 500kWwas conceived to match thethe test aim vessel’s was available power, but the thatpropeller it should diameter not is only generous be a forplatform the loading, so a thruster with fromthe same which diameter scientific nozzle research can handle could up to 1,100kW. be carried out, but also be itself a tool for the development of innovative ma- Gunnerus, owned and operated by NTNU, is equipped to carry out research rine technology. This role Gunnerus in the fields of biology, technology, geology, archeology, oceanography and undertakes in the thruster develop- fisheries. ment work. As built, the ship had diesel electric Prop. curve, operating profile & efficiency propulsion in a traditional twin screw 100% and rudders arrangement. The 90% original high speed diesel gensets are 80% retained, and these are fitted with 70% extremely flexible mountings to stop 60% any structure-borne noise potentially Prop. curve, Operating profile & Efficiency 50% 100% affecting research results. As part of 40% 90% the conversion work the propellers, 30% 80% shaftlines rudders and steering gear 20% were removed, and the sterntubes time & operation power Propulsion 70% Gunnerus operation 10% profile 60% plugged, but the skeg remains in Old propulsion system The thruster and blade shapes 0% place and the afterbody was modified 10%50% 20% 30% 40% 50% 60% 70% 80% 90% 100% has been optimised by use of to state-of-the-arttake the PM azimuthCFD tools. thrusters. AZ-PM40% 1900 Old propulsion system Propeller power Gunnerus operation prole These technology demonstrator PM 30% azimuth thrusters have a rating of 5 500kW to match the test vessel’s 20% Time & Power Prop. Operation available power, but the propeller 10%

diameter is generous for the loading, 0% so a thruster with the same diameter 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% nozzle can handle up to 1,100kW. Propulsion Reliability, performance and efficiency

The AZ-PM thrusters have now been propelling Gunnerus for more than a year as the ship carries out its intensive research support schedule. Since the conversion was from shaftlines and rudders to PM azimuth thrusters with the existing generator sets, exact com- parisons before and after can be made. Bollard pull has increased by 20%, and speed has increased by about one knot over the range for the same input power. Course stabilty is good, and manoeuvrability greatly improved. Station keeping and propulsion thrust response are better, valuable advantages in this type of vessel. Noise readings are similar or slightly lower. The thrusters have each now run more than 1,500 hours troublefree.

PM tunnel thruster performance and reliability has also been verified. The unit run in the quayside test stand for more than 1,300 hours was subjected to severe ice impact testing, with blocks of hard ice deliverd by chute to hit the propeller blades under full load. Instrumentation and inspection revealed no damage.

The TT-PM 1600 installed in Olympic Octopus as part of the AHTS’s DP thruster outfit has lived up to expectations, and has amassed over 5,000 running hours to date.

Permanent Magnet propulsion products

Tunnel thrusters TT-PM 1600 - 0.5-1.1MW TT-PM 2000 - 1-1.6MW TT-PM 2600 - 2.6MW (from 2018) Azimuth thrusters AZ-PM 1900 - 0.5-1.1MW AZ-PM 2600 - 2.6MW (from 2017)

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