Factory acceptance tests on the engines for Grupo Ibaizabal's newbuild LNG bunkering vessel achieved methane slip levels of 0.9%, significantly below the FuelEU Maritime default value of 3.1% for dual-fuel medium-speed engines, according to Wärtsilä.

The 18,600 cbm vessel, under construction at China's Hudong-Zhonghua Shipbuilding, is to be powered by three Wärtsilä 25DF dual-fuel engines equipped with NextDF technology.

Methane slip refers to unburned methane that escapes with exhaust gases from engines using LNG as fuel. Under FuelEU Maritime regulations, which came into force in January 2025, vessels must account for methane emissions on a well-to-wake basis.

Jose Maria Torre, fleet director at Grupo Ibaizabal, said: "Customers have put their trust in us because of our pioneering approach to vessel design, which prioritises low emissions and high operational flexibility. LNG bunkering vessels have an important role to play in supporting the decarbonisation of shipping because LNG is a key transitional energy source for the maritime industry."

The factory acceptance tests are also said to have showed that diesel pilot fuel consumption was 30% lower than initially indicated by Wärtsilä. The engines can operate from 0 to 100% load in gas mode, minimising diesel fuel use.

Torre noted: "Wärtsilä can offer guarantees for engine performance, especially methane slip reduction. These guarantees were backed up by hard data. For us, it was also important that the Wärtsilä 25DF could operate from 0 to 100% load in gas mode, which minimises the use of diesel fuel."

Wärtsilä introduced NextDF technology for the 25DF engine in October 2024, claiming it reduces methane emissions to less than 2% of fuel use across all load points, achieving as low as 1.1% in a wide load range. The technology was first introduced for the Wärtsilä 31DF engine in 2023.

Ibaizabal is said to have secured charters from a major global energy company as a direct result of the low methane slip level of its new LNG bunkering vessel.

Torre stated: "Our charterers are very satisfied with the engine performance, which is a milestone in the industry and has significant reputational value for everyone involved."

Vessels operating below the FuelEU Maritime default methane slip values can avoid financial penalties under the regulation, which sets maximum limits for the yearly average greenhouse gas intensity of energy used by ships above 5,000 gross tonnage calling at European ports.