Complying with EEXI – how to speed up decarbonisation without slowing down vessels

How can shipowners comply with the Energy Efficiency Existing Ship Index (EEXI) and improve the Carbon Intensity Indicator (CII) of a vessel without reducing sailing speeds? In this article we take a closer look at the potential routes for compliance and the alternative technologies available to improve energy efficiency.

In June this year, the IMO’s Marine Environment Protection Committee (MEPC 76) adopted a number of technical and operational measures aimed at reducing the carbon intensity of international shipping. These measures, which apply from 2023, include the Energy Efficiency Existing Ship Index (EEXI), which defines a minimum energy efficiency level for existing vessels, along with the Carbon Intensity Indicator (CII) rating scheme, which gives vessels an annual rating on a scale of A to E, with A being the least carbon intensive.

It is believed that most shipowners will seek to comply with EEXI by adopting either engine power limitation (EPL) or shaft power limitation (ShaPoLi), with the latter potentially being the preferred choice for multi-engine setups. Regardless of the route chosen, the result will be a reduction in the amount of power delivered to the propeller and therefore a potential long-term impact on a vessel’s economic performance.

Weighing up the alternatives

While speed reduction might be a valid option for vessels with high installed power and high design speed, for vessels such as tankers and bulkers, which are designed to sail at much lower speeds, EPL and ShaPoLi solutions may offer limited benefits in terms of commercial flexibility and attractiveness to charterers.

Wärtsilä has recently been working with a customer to examine the operational profiles of one of its bulkers over the last 12 months. In this case, while a speed reduction of 5% enabled by EPL was acceptable when considering the average vessel speed, it would have impacted around 15% of the vessel’s sailing days over the 12-month period when the vessel needed to sail at higher speeds. Another limiting effect of EPL and ShaPoLi is that they do not result in any real impact on a vessel’s carbon footprint and therefore have no benefit in terms of the vessel’s CII rating.

So, what are the alternatives and how can ship owners improve their EEXI without reducing sailing speeds?

Energy Saving Devices (ESDs)

ESDs have a direct impact on vessel propulsion efficiency by reducing hull resistance and improving propeller thrust. Wärtsilä offers pre- and post-swirl devices such as Wartsila EnergoFlow and Wärtsilä EnergoProFin as well as high-performance hull coatings to reduce resistance and fouling. Installing a replacement propeller that is optimised for the vessel’s current operational profile also offers significant potential benefits. Depending on the vessel type, energy savings in the region of 5–10% can be achieved by combining ESDs and an optimised propeller. The problem is that many younger vessels already have ESDs installed, so the room for improvement is limited. For this reason we may see alternative ESDs such as air lubrication systems and wind rotors – which are also part of the Wärtsilä portfolio – continue to gain traction in the market.

Shaft generator systems

Shaft generator systems, which have been around for several decades, aim to cover a vessel’s onboard electricity needs while sailing by utilising the main engine as opposed to the auxiliary engines. With the help of modern converter technologies and software, these systems can produce electricity across a wide engine rpm range. Due to their positive impact on a vessel’s Energy Efficiency Design Index (EEDI – the corresponding index to EEXI for newbuilds) they are now standard onboard most newbuilds, and with the rapidly approaching EEXI deadline there has been a huge increase in demand in the retrofit market as well.

With the potential to improve a vessel’s energy efficiency by 3–5% and reduce both fuel costs and OPEX, shaft generator systems typically have an ROI of around five years for a bulker or tanker, and this period becomes even shorter as the number of sailing days increases. For vessels with existing ESDs, shaft generators are often seen as the next-best technical option to achieve EEXI compliance while reducing OPEX and positively impacting the CII rating. Over 550 vessels sailing today are benefiting from Wärtsilä shaft generator systems.


A hybrid system typically combines an energy storage system and a conventional engine. It is available as both a standard solution for newbuilds and as a retrofit solution for existing vessels. Wärtsilä has been piloting hybrid systems since the dawn of this technology, starting with an offshore vessel in 2011, and is now the market leader in hybrid systems for newbuilds and existing vessels alike.

While a retrofit has obvious advantages for vessels with a dynamic positioning system, where total fuel consumption can be cut by up to 20%, the advantages for merchant vessels are not so obvious. A hybrid system can optimise auxiliary engine utilisation on a merchant vessel, reducing running hours by introducing start-stop logic and optimising fuel consumption.

One thing to note is that the benefits of a hybrid system alone are not yet taken into account in the EEXI formula as it does not reduce the total installed power.

An EEXI impact of 4% and a vastly superior ROI can be expected when the hybrid system is intended to be an integral part of a ‘free power-source technology’ installation such as photovoltaic cells. In addition to the onboard energy optimisation described above, the hybrid system is in this case intended to enable an even greater level of optimisation by integrating the functionalities and productivity of solar power production with onboard auxiliary engines and using batteries as a storage buffer. Wärtsilä is currently piloting such a system.

In addition to enabling immediate energy savings, hybridisation should also be viewed as a bridge to the future. New power-production technologies such as fuel cells and engines that can run on cleaner future fuels will likely require hybrid system integration to ensure safety and operational stability, especially in transient load conditions or when connected to shore-power systems in port.

Future fuels

While future fuels have a critical role to play in helping the maritime industry to achieve the IMO’s target to reduce the carbon intensity of international shipping by 40% by 2030, the path ahead is littered with uncertainties.

LNG is both an established reality in the newbuild market and an excellent option for retrofits; it instantly and drastically reduces CO2, NOx, SOx and particulate emissions. It is well established as a maritime fuel around the world in virtually every vessel segment, with mature legislation frameworks and robust bunkering infrastructure.

Methanol is currently attracting a great deal of attention as an alternative fuel for newbuilds and retrofits. Methanol’s physical properties make it an attractive option, and the use of hydrogen from renewable electricity and recaptured carbon to make green methanol would make it carbon neutral.

Wärtsilä is one of the few marine engine builders to have experience with methanol engines. A project to convert a Wärtsilä Z40 engine on the ro-pax vessel Stena Germanica to burn methanol began in 2015. The engine now runs mainly on methanol, and the success of the installation has inspired Wärtsilä to investigate this fuel further. Learn about Wärtsilä’s holistic Marine Methanol Conversion.

In the longer term, ammonia and ultimately hydrogen represent the 100% carbon-free fuels of the future. Interest in these fuels is increasing, and Wärtsilä has already established itself as a technological leader. Read more in our deep-dive article on ammonia as a marine fuel.

It is clear that all these future fuels can have a significant positive impact on a vessel’s EEXI and CII rating. Nevertheless, their implementation requires significant investment in both bunkering infrastructure and onboard fuel storage and handling systems.

Ensuring optimal engine performance

In the discussion around decarbonisation, vessel owners and operators are faced with an array of options in terms of energy-saving hardware and software. But one basic thing is sometimes overlooked: ensuring that the engines themselves are operating as efficiently as possible. Wärtsilä’s range of lifecycle service agreements is designed to offer the right level of service to ensure just that.

The starting point for optimal engine performance – and therefore minimised emissions – is to make sure that the powertrain is set up to match the vessel’s operating profile. Engine retrofits and improvements in operating the engines can enable substantial fuel savings, and therefore a significant reduction in emissions. Equally important is to ensure that these assets are properly maintained. Every single component has a part to play; for example, exchanging a filter or cleaning an air cooler at the right time can help to cut fuel consumption. Data collection and expert analysis can be employed to identify the optimal timing for such maintenance interventions.

Wärtsilä Lifecycle Agreements are available with varying levels of support depending on the customer’s needs, but all are based on solid, actionable data. The three-layered combination of rule-based limits, anomaly detection and human expertise is what keeps our customers’ assets not just up and running but running in a way that contributes to rather than takes away from the overall decarbonisation efforts of the vessel.

The four pathways discussed in this article – ESDs, shaft generator systems, hybridisation and future fuels – are capable of helping ship owners to comply with EEXI without requiring them to accept a loss of speed; in addition they also improve a vessel’s Carbon Intensity Index rating by reducing the carbon footprint, enhancing its reputation in the eyes of investors and financial institutions.

Share with your friends