ABB’s new, cycloidal-type propulsor concept – ABB Dynafin – significantly increases a vessel’s efficiency and promises to substantially reduce emissions across the marine industry.

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_{Jani Hakala, Janne Pohjalainen, Veli-Pekka Peljo, ABB Marine and Ports Helsinki, Finland jani.hakala@fi.abb.com, janne.pohjalainen@fi.abb.com, veli-pekka.peljo@ fi.abb.com}

Most international trade relies on waterborne transportation. Despite providing the most cost-effective means of moving the goods involved in this trade, the shipping industry suffers from the drawback that ships typically burn heavy fuels that produce greenhouse gases (GHGs), such as carbon dioxide (CO₂), making the marine sector responsible for around 2 percent of human-made CO₂ emissions globally [1]. Indeed, if shipping were a country, it would be the sixth-largest emitter of GHGs worldwide [2].

To address these emissions, the International Maritime Organization (IMO) has declared the ambition to achieve net-zero emissions from international shipping by 2050. Alternative energy sources and advanced propulsion technology are seen as crucial elements of the plan to accomplish this goal.

In May 2023, ABB presented a breakthrough solution that looks set to revolutionize marine propulsion – ABB Dynafin, a cycloidal-type propulsor that meets the urgent demand for higher efficiency and emissions reduction.

ABB Dynafin

The innovative ABB Dynafin generates thrust by means of blades that project outward from the bottom of the ship →01. The blades rotate around their own axis and around the axis of the rotatable wheel upon which they are mounted. In this way, and under the control of a sophisticated control system (see the article “Command and control” on page 174 of this edition), ABB Dynafin can achieve very high hydrodynamic efficiencies and change thrust direction almost instantaneously, giving far better maneuverability than arrangements in which a conventional propeller is rotated about a vertical axis to direct thrust.

The ABB Dynafin concept is essentially a cycloidal propeller with individually controlled blades following a trochoidal path, analogous to that of a whale’s tail. (A trochoid is the curve generated by a point on the radius of a circle as the circle rolls on a fixed straight line.) Trochoidal propellers have been studied before, but until now, technology constraints have prevented them from being commercialized and introduced to the market.

Rotational movement of the main wheel is produced by an electric direct-drive motor. The main wheel rotates at a relatively low 40 to 80 rpm and has four to six identical blades →01. The direction of rotation is kept the same under all operational situations and thrust amount and direction are determined by a combination of main wheel rpm and blade adjustment. Initially, ABB is concentrating on developing ABB Dynafin units in the power range of 1 to 4 MW per propulsor →02.

Models and modeling

The development of ABB Dynafin was greatly aided by using computational fluid dynamics (CFD) simulations to evaluate hydrodynamic performance as well as by scale-model open-water testing →03a-b Much of the detailed work was carried out in collaboration between ABB and a team from the VTT Technical Research Centre of Finland in Espoo, Finland (see the article “Bubbling under,” on page 168 of this edition.)

The next step in hydrodynamic performance testing was to expose ABB Dynafin to conditions closer to those in the real world by retrofitting propulsors to a platform support vessel’s hull. Performance could then be compared against existing Azipod® units in the same power range. Following the successful simulations and scale-model and vessel-hull tests, ABB engaged in productive discussions with several ship design offices, shipyards and ship owners and operators to validate the feasibility of the concept.

Key efficiency factors

Several factors drive the high efficiency of ABB Dynafin, such as its larger propulsive area, which lowers the propeller loading, giving the lowest thrust loading coefficient. The lower this coefficient, the higher the ideal open-water efficiency of a propulsor.

Further, ABB Dynafin’s geometry makes it ideal for shallow-water vessels as it protrudes less far than an equivalent screw propeller. In contrast to a traditional vessel, which has a rudder and struts for the shaft that create drag, a cycloidal propulsor only has the blades protruding from the hull, giving a better hydrodynamic performance.

A further factor that drives efficiency is the ability to control each blade individually. Each blade is controlled by an electric motor, a frequency converter (to control torque and rpm) and control logic. This arrangement enables the imitation of a high-efficiency whale-tail movement and adjustment of the blade movement (eccentricity, advance ratio and angle of attack) depending on different vessel operational situations, maximizing efficiency and thrust in both transit and dynamic positioning modes →04.

ABB Dynafin has a major advantage over fixed pitch propellers, which are optimized to a single operational point, in that it can adjust the movement of the blades continuously to meet optimal performance over a wide speed range and different wake fields. The unit’s control and software technology allows continuous vessel performance optimization throughout its lifetime, creating the concept of a “digital propeller.” ABB Dynafin can also be operated in “rudder mode,” meaning that all the blades are controlled as conventional rudders. This feature brings benefits not only for double-enders and sail--assisted vessels but also increases redundancy in failure situations, providing partial steering capability.

In addition to having a direct electrical power train for both the main wheel and the blade modules, a mechanical bevel gear may be used, allowing connection to the main engine and extending the benefits to vessel segments where electrical power trains are typically not used.

Other efficiency gains can be made because Dynafin’s superior performance allows for smaller power plants (and fuel tanks) to be used. This improvement reduces capital outlay and maintenance costs, enables a more flexible ship layout and frees up room for cargo and passengers. This power-reduction aspect is particularly beneficial to hybrid or fully battery-powered vessels, as the size of costly battery banks can be minimized.

Dynafin vessels make the least noise

Limits on underwater radiated noise are expected in the near future due to its potential effect on aquatic ecosystems. ABB Dynafin minimizes electromagnetic noise by having the electric motors inside the vessel’s hull and minimizes hydrodynamic noise by limiting cavitation and turbulence. In addition, individual blade control enables optimized trajectories to curtail hydrodynamic noise in different operational situations.

High reliability and easy maintenance

ABB Dynafin’s modular structure and high degree of standardization simplify spare part management. There are, in any case, fewer components due to the combined propulsor and steering and a direct electrical power train.

The absence of wear-sensitive gears and the main wheel’s moderate 40 to 80 rpm minimizes component wear, but when component inspection or replacement is needed, the main wheel is easily accessible from inside the vessel.

A sea of application possibilities

ABB Dynafin delivers a fuel consumption reduction of up to 22 percent compared to a conventional shaftline and a propulsion efficiency of up to 85 percent. Less space is needed for the ship’s power plant and fuel tanks. In addition to high efficiency, ABB Dynafin also simplifies maintenance and enables superior vessel maneuverability. ABB’s expertise in hydrodynamics, mechanical systems, ship electrification and automation and control puts the company in a unique position to further improve the ingenious ABB Dynafin. This propulsion system adds a new level of adaptability and intelligence to vessel performance and changes how the shipping industry thinks about propulsion systems.

_{References

[1] Transport and Environment, “Climate impact of shipping.” Available: https://www.transportenvironment.org/topics/ships/climate-impact-shipping [Accessed February 29, 2024].

[2] Statista, “Shipping emissions worldwide – statistics & facts.” Available: https://www.statista.com/topics/11288/shipping-emissions-worldwide/#topicOverview. [Accessed February 29, 2024].

[3] Fasse, G. et al., “An experimental blade-controlled platform for the design of smart cross-flow propeller.” Available: https://www.sciencedirect.com/science/article/abs/pii/S0029801822003547. [Accessed February 29, 2024].}

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