Emissions reduction: methanol and batteries take central stage

There are other fuels to consider, particularly for local markets and individual cases – such as LNG, ammonia, hydrogen and ethanol – but the smart money is on methanol hybrid for the long term, particularly if green methanol fuels can be produced at scale from renewable biosources and energy.

For tug operations, diesel is used due to its energy density and ease of transport, which is why it is so prolific – hundreds of tugs are built worldwide each year, almost all run by two diesel-fuelled main engines, except for a few LNG-fuelled and all-electric tugs. Even these have diesel gensets for back-up. This is why biodiesel alternatives are great for the short-term.

However, the maritime industry will be increasingly competing with aviation and land transport for available sustainable biofuel alternatives, such as hydrogenated vegetable oil (HVO) and fatty-acid methyl esters (FAME) and fuel blends. 

Tug owners are among the largest users of HVO and FAME in the maritime sector, in terms of the number of vessels using them. These are easy drop-in fuels that engine manufacturers have approved and can be purchased almost worldwide. However, there is uncertainty about their environmental credentials and prices are rising rapidly, making them more expensive over time. And if they are used to produce biokerosene, they will become even harder to source. 

Thus, tug owners are seeking alternatives that are green certified, available and promise lower emissions – and let’s not forget the importance of cutting NOx and particulates in ports. Clean and green methanol offers benefits such as its relative ease of storage, as a liquid in ambient conditions; energy density that may only be half of diesel, but is better than the rest; abundance of grey methanol now and promise of green in the future; historical transport and usage in maritime; and similarities to diesel for bunkering. However, it is more toxic and has a lower flash and vapour point than diesel, and seafarers will need training in handling this fuel.

While batteries can be installed on tugs working within harbours with charging infrastructure, if they need range extension then methanol will become an important fuel. In local markets such as Brazil, ethanol could be a decent alternative. There could also be local markets for ammonia, however, its toxicity, semi-cryogenic storage, safety challenges and aftertreatment requirements make it difficult. LNG is a good alternative and the second-most abundantly used fuel in harbour towage but methane slip continues to a challenge, as is its storage and handling. 

Hydrogen may have its uses, but storage, safety and depressurising challenges mean it has limited appeal. Tugs using ammonia now are only pilot schemes to prove the technology; those on hydrogen are mainly state funded; as are those on methanol for now, but that is expected to change.

When the world’s largest tug owners select HVO and FAME blends now and methanol-hybrid propulsion for the future, you must follow the money. After a successful Riviera Marine Fuels Webinar Week, it is clear there is a future for all alternative fuels in the maritime industry. For tugs, that is methanol-hybrid, and this will be a main focus of presentations, debates and discussions at TUGTECHNOLOGY ’25. See you on the world’s first methanol-fuelled and hydrogen-fuelled tugs in Antwerp, Belgium on 19 May.