Vessel design considerations for methanol retrofits

In 2023, the International Maritime Organization revised its greenhouse gas (GHG) emissions strategy, requiring international shipping to achieve net-zero emissions by or around 2050, with a 40% reduction in carbon intensity by 2030. To meet these targets, many owners will need to operate on alternative fuels. However, the capacity of shipyards to build new vessels powered by green energy is limited, making retrofitting existing vessels a critical solution to complement newbuilds.

Retrofitting allows shipowners to convert vessels to operate on alternative fuels like methanol, reducing GHG emissions and enabling compliance with future regulations. Methanol is particularly promising due to its similarities with conventional fuels, which makes it easier to implement in retrofits than other alternatives like ammonia or liquefied natural gas. While methanol presents certain safety risks such as toxicity and flammability, these risks are lower than those from other alternative fuels if proper precautions are in place.

Retrofitting provides flexibility for shipowners to extend the operational life of vessels, especially those between 5-10 years old, while aligning with new environmental regulations. Studies show that methanol fuel retrofits can significantly reduce carbon emissions, especially when using e-methanol or bio-methanol.

The design and technical aspects of retrofitting must be carefully planned to optimize the methanol fuel system, bunkering station, tank arrangements, and overall vessel performance based on the operational requirement. Retrofitting methanol tanks presents several design options, including independent, integral, or on-deck tanks, depending on operational needs and budget constraints. Shipyards must be capable and prepared in handling specialized equipment, methanol-specific technical work, and safety standards related to methanol, while collaboration with engine manufacturers is crucial for successful engine conversions.

This report provides a comprehensive guide to shipowners, operators, ship designers, and shipyards on designing and planning a successful methanol retrofit, underscoring the main technical considerations while complying with regulatory requirements.

The report covers safety, technical, regulatory, and commercial aspects of methanol retrofits.

Topics covered include:

• Assessment of applicable regulations, guidelines, and regulatory gaps or inconsistencies
• Analysis of options for methanol fuel systems (with case studies)
• Explanation of the potential impacts of retrofitting on vessel design and performance
• Options for optimization of methanol retrofits
• Overview of the shipyard technical requirements and capabilities needed for successful methanol retrofits

Designers and shipyards need to balance many considerations when choosing methanol fuel tank types, locations, and capacities:

• The tank type and material should reflect the specific vessel’s operation and budget
• Independent tanks are technically simpler to install
• Integral tanks maximize the vessel’s endurance with minimal structural changes.
• Portable tanks allow quick and flexible bunkering
• Stainless steel is more expensive upfront, but more durable and less technically complicated to install than zinc-silicate-coated steel

The location of methanol tanks must balance ease of installation, stability, capacity, and cost:

• Open-deck tanks are simple to install
• Tanks in the cargo hold improve vessel stability but reduce cargo space
• Double bottom/side/topside tanks maximize fuel capacity and cargo volume, but are complicated to install

The size and capacity of methanol tanks must reflect the vessel’s operational profile, balancing endurance, bunkering frequency, and cargo capacity. With careful and appropriate planning, retrofit designs can be optimized by lengthening the vessel or repurposing existing ballast tanks as cofferdams or fuel tanks.

Shipyards carrying out methanol retrofits need strong project management, careful planning, and the ability to handle procurement of specialized equipment, electrical work, and strict coating procedures. High safety standards and good collaboration with engine manufacturers are also essential.

The insights and advice contained in this document can help shipyards, ship designers, and shipowners plan and carry out successful methanol retrofits, supporting benefits both for individual stakeholders and the decarbonization of the shipping industry as a whole.