Business Sectors
Events
Contents
Register to read more articles.
Pilot viewpoint: best options are HVO, methanol and batteries
Uzmar pilot Mustafa Sokukcu reviews the options for tug owners to reduce emissions using alternative fuels and energy storage solutions
Lowering fuel consumption and greenhouse gas (GHG) emissions from the shipping industry has emerged as one of the most dominant concerns of the maritime sector, driving interest in developing alternative fuels and green propulsion technologies, which have pros and cons compared to diesel fuels.
The main alternative fuels include methanol, ammonia, hydrogen, LNG and biofuels, and technologies like electric energy, batteries, fuel cells and hybrid/dual-fuel systems. Although the alternatives are cleaner and promise lower emissions than diesel (MGO) fuels, there are many uncertainties when using them in tugboats, including suitability, availability, useability and cost.
Alternative fuels
Methanol is a significant alternative since it may be supplied and stored on a tugboat, and its energy density is similar to diesel fuels. But its flash point is low, so even a small amount of flammable material can cause a fire.
Another disadvantage is methanol is water-soluble; using water alone will be insufficient for fire fighting. Methanol is harmful to human health, meaning storing it on tugboats carries risks making safety precautions vital.
There is not enough methanol production capacity, and the supply infrastructure has not yet been established. It can be used together with MGO as dual fuel in newbuild tugboats due to its storage and replenishment properties. Compared with diesel, methanol will take up around twice as much space on the tugboat in terms of volume and weight.
Ammonia is an alternative in terms of compliance with emissions, but it has disadvantages such as a lack of infrastructure, not being easily accessible, and not being tested at sufficient levels.
It is an extremely toxic chemical that must be cooled to -33˚C or kept under pressure to store as a liquid. Since it requires six to seven times more storage space on the tugboat than diesel fuels, its application does not seem possible at this stage, except on oceangoing vessels with enough storage space.
Hydrogen is difficult and risky to store on a tugboat for safety reasons. Its flammability and explosivity are high and it requires very large volumes of storage. Other disadvantages are the lack of trials with this fuel and undeveloped production technologies.
Supplying hydrogen to the tugboat is a difficult, lengthy operation. It must be cooled in its liquid form to -253˚C, or highly pressurised, increasing maintenance costs on fuel pipes and equipment in the medium and long term. It is not currently considered possible to use due to the high volumes requiring storage on the tugboat and the complex cooling system requirements to keep it in liquid form.
Liquefied natural gas (LNG) is a fossil fuel with no sulphur, low NOx emissions and less CO2 than MGO. It is already used on tugs, and engine technology and infrastructure is available for newbuilds and retrofits.
But LNG is not completely carbon neutral and needs four to five times more storage space in tugboats compared with MGO. LNG also needs to be cooled at very low temperatures when stored in liquid form. This will increase freezing-related wear on fuel lines and equipment in the long term and increase maintenance costs. Keeping it under pressure also increases the risks. Another big concern for tugboats operating in narrow places and dangerous waters is safety measures.
Hydrotreated vegetable oil (HVO) biofuel is one of the most important alternatives to diesel fuels, especially for tugboats. It has 99.9% biofuel content and promises zero emissions in terms of well-tank-wake emissions.
HVO is being used on tugboats in the UK by Svitzer. It can be used in the engine of existing tugboats without modification, which is a lower-cost solution compared to other alternatives. It has similar properties to diesel oil in terms of storage and safety in the tugboat.
Further technologies
These fuels can be combusted in engines or generators, or could be used with fuel cells, which have attracted great attention recently with their advantages, such as having a higher energy density compared to batteries and taking up less space on the tugboat. Engine manufacturers are conducting research on fuel cells that can operate with different fuels, and among these, hydrogen appears to be the most important option.
There are projects based on the principle of obtaining hydrogen by processing methanol or ammonia and producing hydrogen from seawater through electrolysis using electricity from renewable resources.
Fuel cells are not being fully assimilated yet and standards are limited. Storing hydrogen on the tugboat is challenging and the cost of installing fuel cells is high compared to other alternative fuels.
Batteries are one of the most important alternatives for zero emissions and are increasingly used in tugboats. The necessary infrastructure and technology requirements have also been determined.
The biggest disadvantages of current battery technology today (based on lithium ion) are their large size, required storage space and high cost. The initial production costs for battery powered tugs are 1.5 times higher than diesel tugboats. The operational costs are lower than other alternatives and at approximately the same level as diesel fuels. The lifespan of batteries and their subsequent recycling or disposal processes are also important criteria.
Factors such as charging the batteries too many times and how low the charge level is before charging can play a role in extending the life of the batteries. Another important point is whether the battery modules have safe management systems.
Furthermore, when replacing a battery, it is critical to consider if the appropriate battery is readily available or compatible with other battery types. The safety precautions and storage conditions required by batteries on the tugboat are other negative aspects.
Batteries pose a fire risk, and battery fires take a long time to extinguish. Sparks and fire may occur due to seawater leaking into the battery compartment, so they must be insulated and watertight.
There should be no leaks from the condensation circuits of the cooling system onto the batteries and no seawater ingress through the ventilation gaps, while their high voltage poses a danger to the crew. Other disadvantages are charging infrastructure in ports is insufficient and electricity is still not green.
Conclusion
Pure biofuel, such as HVO, appears to be the most important potential alternative because it can be used in existing tugboats without requiring engine modifications and is currently being produced in the market, but production costs need to come down.
Methanol is another important alternative. Although there are safety concerns, methanol is less dangerous and less harmful than other potential alternatives and is relatively easier to supply and store on tugboats. Compatible tugboat engines need to be developed and tested for methanol.
Batteries on electric tugboats can do three consecutive manoeuvres under normal port conditions, so different power charges are required. Therefore, hybrid-electric systems appear to be a preferable and sustainable model, as they promise the potential to reduce emissions and safer manoeuvring operations compared to batteries alone.
For electric tugboats, instead of charging from a single point within the port area, charging stations can be positioned at a distance from each other, allowing charging in the gaps between manoeuvres, or there may be floating charging stations.
The proportion of alternative fuel tugboats produced worldwide in the last three years is below 5%; and it seems the most common alternative fuel trial is full electric or diesel-electric. In terms of capital costs, HVO, methanol and electricity are preferable. The biggest advantage of HVO is it does not require modifications. Methanol and electricity offer solutions close to each other in terms of price.
The 27th International Tug & Salvage Convention, Exhibition & Awards will be held in association with Caterpillar in Dubai, UAE, 21-23 May 2024. Use this link for more details of this industry event and the associated social and networking opportunities; and this link to book your ticket for the exhibition, social gatherings and awards night.
Related to this Story
Events
Maritime Regulations Webinar Week
16 Dec 2025
GMT - ONLINE
Floating energy: successfully unlocking stranded gas using FLNGs and FSRUs
24 Feb 2026GMT - ONLINE
© 2024 Riviera Maritime Media Ltd.
