Thruster companies are investing in control and condition monitoring systems that will make pods more reliable and affordable for shipowners
When Scandlines chose to upgrade the thrusters on its four hybrid ferries, running between Puttgarden in Germany and Rødby in Denmark, control improvements were a key factor. The company will spend more than €13M (US$14.7M) replacing CTZ35 thrusters provided by Rolls-Royce Commercial Marine with new AZP120 pulling azimuth thrusters.
The pulling thrusters – four per vessel – provide a more homogenous flow of water into the propeller because the stream is not interrupted by the gearbox casing. The result is a more efficient propulsion arrangement and, critically for Scandlines, less noise and vibrations.
The control and automation system relating to the power and propulsion will also be upgraded, offering further efficiencies. According to Rolls-Royce vice president service sales Kjetil Nilsen, Scandlines is taking “a smart approach towards a greener fleet”.
“Our tests of the chosen solution have shown a significant efficiency improvement, which will deliver a reduction of CO2 emissions,” he said.
Meanwhile, Rolls-Royce's investment in the systems behind thruster technologies is continuing. It recently filed two patents that may eventually improve the condition monitoring of azimuthing thrusters.
One of the difficulties of monitoring azimuth thrusters involves reliably powering sensors in the thruster body and transferring data from the rotating to the static part of the thruster. One current method of doing so involves using mechanical slip rings to convey data and power, but this has two major limitations: the first is cost, as slip rings need to be modified for each size and configuration of the thruster; the second is the wear this arrangement causes to the slip ring and shaftline, meaning regular service is needed.
“The power and data transferring parts of the condition monitoring unit can be retrofitted without removing the thruster from the ship’s hull”
Rolls-Royce energy and health management specialists Werner Schiffers and Lars Saarinen believe the answer lies in resonant magnetic induction. Two inductors – one generating a magnetic field, the other generating an electrical current from that field – are configured so they can be rotated fully while still creating the electrical current. This enables power and data to be transferred wirelessly.
“This would simplify wireless data and power transfer during health monitoring of marine thrusters,” said Mr Schiffers. “A major advantage of our idea is that the power and data transferring parts of the condition monitoring unit can be retrofitted without removing the thruster from the ship’s hull.”
There are other benefits too, stemming from the more robust and efficient transfer of power. The sensor in the thruster body would not require a battery, for example, and maintenance intervals could be extended as thruster designs are adapted to accommodate bigger, longer-lasting inductors. The commercialisation of the concept is not yet in sight, but it provides an intriguing example of how control and automation technology can influence the development and performance of thrusters.
ZF Marine has recently introduced a condition monitoring system for its thrusters. The system measures vibrations which indicate the condition of the bearings and gears in the thruster's upper and lower gearbox. This helps operators to identify when early components need to be replaced or maintained. Repairs can be planned and a worsening in the condition of the components can be avoided, all of which prevents downtime and shortens maintenance time. This extends the service life of the monitored systems and components, allowing the operators to concentrate on their main job.
Monitoring and control are crucial to operating thrusters effectively
The company has also introduced an oil cleaning system to improve the quality and service life of thruster oil. By heating up the oil, the water is evaporated while a cotton filter filters out the particles down to 1 µm. Clean oil is pumped back into the system which extends the service life of the oil by 10 to 15 times. Fewer oil top-ups are needed, saving ship operators money.
ZF Marine sales manager Peter Toxopeus says: “Particularly with biodegradable oil, it is important to keep contaminants, such as water, out of the system so as to prevent downtimes caused by mechanical failures.”
Meanwhile propulsion has been selected for another advanced vessel in Norway, where fertiliser company Yara and Kongsberg have chosen pulling azimuth pods and bow thrusters for the world’s first fully electric and autonomous container ship, Yara Birkeland.
Norwegian propulsion company Brunvoll beat competition from a wide field to win the deal for the high-profile project. It will supply two PU74 pulling azimuth thrusters of 900 kW and two FU63 tunnel thrusters of 700 kW each. The pods and bow thrusters feature highly efficient, big, slow-turning propellers of 2.2 m and 1.75 m diameter respectively.
Brunvoll collaborated closely with naval architect Marin Teknikk to optimise the hull and propulsion. The companies conducted multiple model tests to deliver an efficient configuration, including streamlining the thruster gearboxes.
Brunvoll vice president of sales and marketing Per Olav Løkseth said that the company’s strong relationships and reputation helped it secure the fiercely contested contract. The flexibility to deliver the propulsion arrangement within a tight timeframe was also crucial, he said.
Yara Birkeland will be powered by a 6.8 MWh battery pack when it is delivered in 2020. The vessel will transport fertiliser between Yara’s factory at Herøya and the ports of Brevik and Larvik, cutting around 40,000 truck journeys a year.
Bakker repairs Stena Line bow thruster engine
Sliedrecht-based Bakker Repair and Services has repaired the bow thruster engine of a Stena Line ferry Stena Saga within a week of failure. Bakker was hired by Danish electro-technical company Scanel International.
Scanel removed the engine from the ship and transported it by road to Sliedrecht. The 3.5-tonne electric motor was dismantled and inspected, revealing that a complete overhaul was required. The rotor had to be repaired and the stator needed rewinding. Within a week the engine was assembled, tested and sprayed externally. A day later, the repaired engine could be transported back to Denmark to be re-installed.
"Such a job normally takes up to two and a half weeks, but we didn’t have that much time.” says Bakker Repair + Services sales support co-ordinator Sander Peters.
Bakker Repair + Services specialises in the rewinding of electric motors, transformers and generators. It has its own rewinding shop with computer-controlled equipment. In the case of the bow thruster engine, buying a new engine would have been more expensive and would have taken longer, with delivery times of up to two months.