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Tugboat propulsion evolves to reduce emissions
Electric propulsion and large propellers will reduce tugboat emissions while new concepts are developed
Thruster manufacturers and system innovators are tackling the challenges facing the towage industry which is adopting new technologies on tugs. Propulsion equipment is being adapted and new technology developed, enabling tug owners to reduce emissions without impacting performance in coastal and harbour towage.
Berg Propulsion managing director for the western hemisphere Jonas Nyberg presented the main propulsion configurations for next-generation tugs at Riviera Maritime Media’s TUGTECHNOLOGY ’23, held in Rotterdam, the Netherlands, 22-23 May.
Variable-speed engines, permanent magnet motors and small power-bank batteries on tugs with no onboard generator sets were discussed. “It is about finding ways to be more sustainable and looking at overall system efficiency,” said Mr Nyberg.
For example, tug owners looking to cut emissions can select an azimuth thruster with a larger fixed-pitch propeller, such as 3.2 m, to be driven by a high-speed engine generating 2,240 kW of power, instead of a 2.8 m fixed-pitch propeller that requires a larger engine developing 2,575 kW and more emissions.
In another example, Mr Nyberg laid out a concept of connecting a generator on the main engine for running hotel loads on tugs and removing the independent generator set from the vessel. This provides redundancy for electric steering, which is more efficient than hydraulic-drive steering systems.
Mr Nyberg also suggested introducing cross connections between the two main engines and thrusters on a tug, “so if there is a failure of the generator or motor, there will be no loss of power to the thruster nor steering.”
To improve efficiency further, and to provide an energy boost, two small power banks could be added to tugs, one on the port and the other on the starboard.
“In future, there would be no need for gensets,” Mr Nyberg said. “There would be energy savings and more redundancies for steering. Batteries would be the engine buffers.”
These tug propulsion configurations – two main engines with linked generators and small batteries – would allow future fuels to be adopted on tugs, reducing emissions without impacting safety. “This would be a way to run a main engine on methanol and not have gensets running on diesel,” said Mr Nyberg.
Schottel director for product management and business intelligence Jan Glas considered the latest propulsion solutions for reducing a tug’s carbon footprint. He provided a holistic evaluation of fuel consumption data and examined future configurations for azimuth thrusters.
Results from monitoring tug performance and simulator analysis suggest tug owners and naval architects could save up to 5% on fuel by changing azimuth thrusters on newbuilds.
“Know your operations, targets and design philosophies,” Mr Glas said. “Change the way to design the whole system – there are potential savings.”
Schottel monitored the performance and fuel consumption on PSA Marine’s Singapore-based harbour tug PSA Thor.
This 2018-built, RAmparts 3200 design tug has twin Cat 3516C HD engines and two SRP 510 fixed-pitched rudderpropellers. It has a full speed of 13 knots, bollard pull ahead of 82 tonnes and astern of 78 tonnes.
Schottel measured the performance of the thrusters, fuel consumption and collated data from engines, oil flowlines and bridge systems, collecting 3.2 GB/day of data since 2020.
“We used deep-learning algorithms to cluster data into operations: light bollard pull, heavy bollard pull, eco-transit, high-speed transit and standard tug operations; and monitored fuel consumption in these scenarios,” said Mr Glas. Bollard pull had the greatest influence on fuel consumption, followed by high-speed transits between jobs and berths.
“The present example shows an adapted optimisation strategy for the propeller design has clear potential for fuel savings and thus a reduced environmental footprint,” he said.
“An open dialogue between all parties involved about future requirements and solution strategies could lead to more sustainable towage operations. Electric or electrically assisted drive concepts could benefit from greater design freedom.”
ABB has developed a new propulsion concept for transit, ship assistance and dynamic positioning (DP) applications, with expectations this can reduce energy consumption by up to 22% compared with conventional shaftlines. The ABB Dynafin concept consists of an electric motor powering "a large wheel rotating at a moderate 30 to 80 rounds per minute" with a series of vertical blades that extend from the wheel, each powered by an individual motor and control apparatus.
The combined motion of the wheel and blades generates propulsion and steering forces simultaneously, enabling operational efficiency and precision for vessels. The concept follows ABB’s proven design philosophy in marine propulsion of gearless power transmission.
ABB Marine & Ports global product line manager for marine propulsion Janne Pohjalainen estimates the technology, still in its concept stage, will reach prototype stage in 2025. “We plan to have this ready in 2025 and have a pilot delivery in 2026,” he said.
His team has worked for more than a decade developing the Dynafin system, inspired by the dynamic motions of a whale’s tail, he said.
“Dynafin has been tested at model scale on a ship hull and using computational fluid dynamics and algorithms,” said Mr Pohjalainen.
In studies by Japanese maritime design and engineering consultancy OSK-ShipTech, Dynafin propulsion was verified using 22% less propulsion energy when compared with a conventional shaftline configuration.
“It will initially be available in the power range of a 1–4 MW unit. It will be highly efficient for offshore support vessels, tugboats, harbour vessels and yachts, and especially good for DP operations and for fast steering.”
Dynafin is fully compatible with zero-emissions battery and fuel-cell technologies, and reduces vibrations and noise levels, improving crew comfort. “Each blade can be individually controlled and moves like a whale tail,” said Mr Pohjalainen. “It is radical and efficient and supports fast changes in thrust direction. It is a giant leap from what is currently available.”
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