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Electric propulsion key to a zero-emissions future in cruise

Technological advancements are a natural part of the evolution of the cruise industry – from oars and sails to steam and diesel. Electric propulsion systems are the latest step in this progression

In the last few years, regulators in the maritime industry have set lofty goals for carbon emissions reduction and improving energy efficiency. While much of the progress towards these goals depends on adopting future fuels, electric propulsion systems also can play a critical role, especially in the cruise segment, which is uniquely sensitive to public pressure and customer feedback.

Fortunately, the cruise segment has been at the forefront of adopting electric propulsion technology.

In 1995, a landmark project on the Costa Victoria became the first integrated electric propulsion system installed on a cruise ship by Wärtsilä. The electric propulsion system linked all onboard systems from bridge to propeller including automation, navigation, electrical distribution, the switchboard, and complete cabling.

By connecting to Costa Victoria’s decentralised power management system, the electric propulsion system optimised load sharing, frequency control, protection for gensets, and automatic black-out recovery. It was seen as a revolution in the cruise segment, and electric propulsion systems have continued to evolve ever since.

Approximately 60% of ships were using electric propulsion systems by the end of the 1990s, and today it is the cruise industry standard to implement electric propulsion systems for newbuilds, according to Uwe Heine, Chief Technologist, Marine Electrical Systems at Wärtsilä.

Heine has been working in the industry for 27 years and has witnessed the dramatic expansion of electric propulsion systems. He remembers the installation of the first electric propulsion system on the Costa Victoria and has monitored the progression of the technology ever since.

“It’s an evolution, not a revolution,” he says. “The basics are still the same. Diesel engines and driving electric generators that form the power station that supplies everything on board of the vessel.”

Optimising efficiency

Maritime vessels need constant sources of power to operate not only the propellers, but also every other system onboard. Ship engines, the tunnel thrusters, galleys, air conditioning and the hotel load require electricity to operate, and without it, a vessel would cease to function. Without the power station principle, vessels require at least two power sources in order to maintain both electrical systems and propulsion. On the other side, an electric cruise ship is able to operate with only one engine at low load.

With an electric propulsion system, a vessel’s engines are not connected to the propeller shafts. Rather, engines are linked with electricity-producing generators that power electric motors. The newest technology for these motors is with permanent magnets at the rotors. By this evolution in design, the propeller shaft optimises efficiency at a 25% reduction – from 8% losses with a traditional electric excited motor to only 6% losses with permanent magnet technology from generator shaft to the propeller shaft.

Benefits to passengers

Electric propulsion systems not only optimise ship operations in a variety of capacities, but also help improve the number one focus on cruise ships: passenger safety. According to Heine, Wärtsilä specialises in crafting integrated electric propulsion systems portfolio with safety features that go above and beyond what regulations require. These extensive backup systems are necessary since losing total electrical power is not an option onboard a cruise ship full of passengers.

Electric propulsion systems can also help increase passenger comfort because these systems make very little noise and produce no vibrations.

Hybridisation

In the 1990s, when the landmark project Costa Victoria was delivered, electric propulsion was an attractive option due to efficiency and reliability, and its potential for enabling OPEX savings.

Seen as such, it existed in competition with more traditional propulsion systems, to be judged on a fairly typical ratio of investment to measurable value.

Today, with the advent of hybrid, electric propulsion can be considered in a different context.

While the systems themselves perhaps demonstrate only modest "evolution," according to Heine, the introduction of an electric power system to a vessel paves the way towards total hybridisation. This has also guaranteed a future-proof, sustainable, and efficient upgrade path for customers who undertook the choice to invest in electric propulsion systems.

The key to a zero-carbon emissions future is hybridisation between electric propulsion systems and diesel engines, batteries, and fuel cells, because at the end of the day, all systems are linked by electricity.

Wärtsilä’s electric propulsion systems were designed to have low lifecycle costs for maintenance, repairs, or spare parts and are even hybrid-ready for older vessels. Electric propulsion systems also decrease carbon emissions and fuel consumption, which improves the overall sustainability of the vessel, as well as maximising efficiency and optimising gensets to meet power requirements across a range of speeds.

“At Wärtsilä, we have people who specialise in the engines and systems integrations and hybridisation and the electric propulsion systems,” Heine says. “Everyone at Wärtsilä is available and is working jointly together to develop a cohesive portfolio. Wärtsilä has developed energy management systems that link together all of the hardware and the software which produce energy.”

Digitalisation

Connecting electric propulsion systems to computers and utilising remote service options have been a part of the cruise segment since the 1990s. According to Heine, even the earliest electric propulsion systems utilised remote service and today increased digitalisation plays a key role in data collection to continue to advance technology onboard cruise ships.

Digitalisation also plays a key role in data collection, which helps continue to advance the technology onboard cruise ships. By digitally connecting a vessel’s systems to shore, voyages can be optimised to reduce fuel consumption, cruising speeds, port arrival times, and routes based on weather patterns and other factors. Data also becomes more transparent as it can be shared with stakeholders in real time.

By investing in digitalisation, ship owners are able to make the most of technological advancements and capitalise on enhanced optimisation, data collection, and interconnection between onboard systems. The future of the maritime industry is increasingly digital, and vessels that invest in digitisation are at the front of the curve.

Looking to the future

Heine says that given the technology available today, running diesel engines on liquefied natural gas (LNG) in combination with batteries is more efficient than using fuel cells. It is also cleaner since the engines run with no visible smoke and produce less nitrogen gas, which means batteries are particularly desirable for use in highly protected areas such as the Norwegian fjords, especially as the cruise segment expands into developing more exploration cruises into remote or protected locations.

“Evolution is driven by society,” Heine says. “Society is now aware that we have environmental issue we need to solve, and electric propulsion systems are the base for zero emissions.”

Ships that operate with hybridisation using batteries also can decrease operating hours, maintenance needs, lubeoil costs of the engines, and increase fuel savings. With diesel propulsion, ships can also use bio-hybridisation to allow for better utilisation of the engine. Someday Heine predicts larger batteries will even be able to power ships without an engine.

Ultimately, the goal, according to Heine, is to continue to advance and find better sources of green energy. Batteries and fuel cells are only the beginning, but new types of fuel – such as liquid hydrogen or ammonia – that have been expensive up until now, may play a greater role in the future.

Wärtsilä is currently investigating several future fuels including synthetic methane, ammonia, hydrogen, and methanol with the goal of providing fuel flexibility around the globe and across engine types. With modern technology, internal combustion engines are adaptable to burn all fuel types and dual-fuel, or spark-ignited engines, are capable of burning LNG, while diesel engines can run on liquid biofuels, biodiesel or e-diesel. Other sources of power are being explored such as solar hybrid power plants also provide clean, sustainable energy to power the maritime segment.

“The sources of energy create an ecosystem; everything is linked to each other,” Heine says.

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