Open call for evidence

Decarbonising smaller vessels

Published 25 March 2025

Purpose and aims

The new maritime decarbonisation strategy sets out the government’s aim for UK domestic maritime to achieve net zero fuel lifecycle greenhouse gas (GHG) emissions by 2050.

This will also deliver wider environmental benefits including for air quality, which will support the government missions to become a clean energy superpower, kickstart the economy and ensure people live well for longer.

The strategy includes a commitment to introduce emission reduction measures for vessels below 400 gross tonnage (GT) and in targeted subsectors, recognising that some subsectors will be able to decarbonise more quickly than others.

This call for evidence (CfE) is intended to gather further evidence to inform policy making relating to this commitment and to ensure that government interventions are effective, proportionate, well timed and meet emission reduction goals.

We are seeking input from a wide range of stakeholders. If you would like to provide evidence for a subsector not listed below, then please do so by specifying the subsectors and vessel types being discussed when answering the questions.

Aims of this call for evidence

In this CfE, we will be gathering evidence on:

• the current and expected future capital and operational costs of zero, or near-zero, emission vessels
• the current technology available and expected future technology developments to enable the transition away from traditional fuels such as diesel heavy fuel oil, marine diesel oil and marine gas oil
• the type and quantity of GHG emissions and air pollutants emitted by traditionally fuelled and zero, or near-zero, emission vessels
• the shipbuilding capacity and capability of UK shipyards to build and retrofit zero, or near-zero, emission propulsion vessels
• the infrastructure, such as refuelling, shore power and charging capabilities at ports/marinas/harbours, currently in place and the future infrastructure needed to enable this transition
• current access to finance to buy and build zero, or near-zero, emission vessels
• issues of compliance and implementation, for example, there is no vessel registration system for many subsectors
• the different methods of data collection and whether systems are already in place to measure emissions
• any opportunities or barriers to this transition

Background

Domestic shipping was responsible for emitting around 7 million tonnes of carbon dioxide equivalent (MtCO2e) in 2019 (6% of domestic transport GHG emissions)^{[footnote 1]}.

The UK’s share of international shipping emitted a further 7.5MtCO2e. In relation to air pollution, domestic shipping contributed 86.8 kilo tonnes of nitrogen oxides (NOx) emissions in 2021 (29% of domestic transport’s NOx emissions)^{[footnote 2]}.

The UK became the first major economy in the world to set a legally binding target to reach net zero emissions by 2050, under the Climate Change Act. This requires the UK government to set legally binding carbon budgets, which determine the maximum amount of GHGs that can be emitted in the UK over a 5-year period. Achieving this requires a reduction in GHG emissions across all sectors of the economy and across all modes of transport.

Decarbonisation measures can also deliver other positive environmental impacts, particularly in reducing air pollution. The Environment Act 2021 set 2 new legally binding air quality targets in England by 2040:

•  a 35% reduction in population exposure to fine particulate matter (PM2.5)

•  a maximum PM2.5 concentration of 10 micrograms per cubic metre (µg/m3).

Meeting these targets will require action on precursor pollutants, including NOx.

The maritime decarbonisation strategy is the government’s preferred way to meet these environmental commitments and our 2050 and interim GHG goals for the maritime industry.

Smaller vessels

Vessels below 400GT are not captured by the other policy measures set out in the maritime decarbonisation strategy, such as carbon pricing or fuel regulations, which will target larger vessels (initially those over 5,000GT). However, it is essential the government takes action across the whole maritime sector to meet our goals, ensuring that action taken is proportionate, workable and effective for this diverse sub sector of maritime.

As set out in the strategy, policies are underpinned by Department for Transport (DfT) maritime emissions model. Data from automated identification systems (AIS) transponders forms the basis of the model. A key challenge for the subsector is the relative lack of emissions data as currently only vessels of 300GT or above are required to have AIS transponders. This CfE will help plug this evidence gap to develop effective and impactful policies.

The government welcomes the input and support of respondents, as the data provided for this CfE will assist the long-term development of the maritime emissions model. By providing much needed evidence on subsectors and vessels that are currently underrepresented, the model will more accurately represent a comprehensive view of the sector, enabling us to continue developing effective and targeted policy measures.

Targeted subsectors

We are also seeking evidence about vessels in targeted sectors that could ‘move quickly’ where there are clear or advanced technological pathways for decarbonisation.

Through stakeholder engagement and evidence from projects funded through the government’s UK Shipping Office for Reducing Emissions (UK SHORE) programme, we have considered the following factors to assess those with clear and unclear pathways.

Vessel operations

The nature of a vessel’s operational activities impacts the ease with which it can reduce its emissions. For example, vessels that operate close to shore may be able to reduce their emissions more easily as there is more frequent access to refuelling and/or charging infrastructure.  However, we recognise that there will be exceptions.

Vessel design

Larger, slower vessels may be able to reduce their emissions more easily for a given operational cycle, as the energy needs are proportionally less than smaller, faster vessels.

Larger, slower vessels are also more flexible in terms of:

• carrying capacity
• space
• volume on board to fit batteries, alternative fuel tanks and propulsion systems

Existing case studies

There are examples of zero, or near-zero, emission propulsion systems already in use, or being trialled, including as part of the UK SHORE programme. We have assessed projects from a variety of subsectors and used the data gathered to inform our understanding.

Through the application of these 3 factors, we have identified small vessels that have a clear route to decarbonisation. These are vessels that have:

• short duty cycles
• regular opportunity to recharge
• space on board for sufficient battery or hydrogen storage

We have paid particular attention to cases where a representative technology demonstrator is present. This includes:

• offshore wind operations and maintenance vessels
• inland waterways vessels – this includes boats that can no longer be moved under their own propulsion, but excludes fixed floating platforms and structures that are used for permanent dwellings and have no means of self-propulsion
• recreational craft – this excludes personal watercraft, as per Recreational Craft Regulations 2017
• ferries – this only includes ferries travelling between UK ports
• aquaculture vessels – service the aquaculture sector which includes the breeding, raising and harvesting fish, shellfish and aquatic plants
• port service vessels – vessels that support the operations of a port, for example dredging vessels and tugboats

The subsectors we have identified as currently having an unclear pathway to reducing emissions include but are not limited to:

• oil and gas operations and maintenance vessels
• deep sea tugs
• pilot boats
• pipe layer/cable layer vessels
• research vessels
• salvage vessels
• lightships^{[footnote 3]}
• fishing vessels

We want to understand the individual subsectors as fully as we can, which is why we are launching this CfE. Once the CfE has concluded and we have analysed the responses, we will aim to publish a summary of responses in 2025. As we continue to develop this policy, we will continue to engage with the relevant subsectors.

Gathering evidence on individual subsectors is an important first step and does not mean these subsectors will necessarily be impacted by future policy. Any policy which is developed following this CfE will be subject to appropriate consultation.

Policy context

The wider context in which these polices are being developed is set out below.

International Maritime Organization (IMO)

The 2023 IMO Strategy on Reduction of GHG Emissions from Ships set a target for GHG emissions from international shipping to reach net zero by or close to, 2050.

It included interim emissions reduction checkpoints to reduce the total annual GHG emissions from international shipping by 20% to 30% by 2030 and 70% to 80% by 2040, compared to 2008 levels.

The strategy also set a target to increase the uptake of zero or near-zero GHG emission technologies, fuels, and energy sources to make up 5 to 10% of the energy used by international shipping by 2030.

To deliver these targets, IMO member states are developing a package of global regulatory measures, including an international fuel standard, which are due to be approved in spring 2025 and enter into force from 2027.

Maritime decarbonisation strategy

The maritime decarbonisation strategy complements international action regulated through the IMO and explains how the maritime sector will reduce its emissions to support delivery of legally binding UK carbon budgets and net zero.

It sets out our aim for UK domestic maritime sector to achieve zero fuel lifecycle GHG emissions by 2050, with at least 30% reduction by 2030 and 80% reduction by 2040, relative to the 2008 baseline.

Policies to meet these aims include:

• extending the UK Emissions Trading Scheme (ETS) to maritime from 2026

• introducing domestic fuel regulation to complement IMO measures

• introducing measures to reduce emissions from vessels at berth and wider port operations.

The maritime decarbonisation strategy will also deliver wider environmental benefits.

A separate CfE about net zero ports has been launched alongside the Strategy and this CfE. Both CfEs ask for evidence about port infrastructure and capabilities. We will share evidence from both CfEs to ensure joined-up policy development.

UK SHORE

UK SHORE is a £236 million programme within DfT focused on the technology necessary to decarbonise the maritime sector through investment in research and development.

Projects include:

• Tidal Transit, which has developed a zero-emissions capable vessel with modular batteries and range extenders on board, offering significant emission savings of 50 to 100% for the majority of wind farms

•  MJR Power and Automation, which has completed a trial at the Port of Blyth enabling all heavy hybrid and electric crew transfer vessels to connect in the field to a 100% green energy source generated directly by offshore wind turbines for power

Operation Zero

Launched at COP26 in November 2021, Operation Zero is an industry coalition working together to accelerate the decarbonisation of the operations and maintenance vessels in the North Sea offshore wind sector, with a view to making zero emission operations and maintenance vessels a reality in 2025.

Renewable Transport Fuel Obligation (RTFO)

Existing policy on fuel supply to encourage the use of zero and near-zero emissions fuels includes the Renewable Transport Fuel Obligation (RTFO), which is a certificate trading scheme to incentivise the use of renewable fuels in eligible modes of transport (including inland waterway vessels that do not normally operate at sea).

In 2021, the RTFO was amended, making renewable fuels of non-biological origin (RFNBOs), such as electrolytic hydrogen and ammonia used in maritime, eligible for support.

How to respond

See the Ways to respond section of the consultation page on GOV.UK to find out how you can respond to this consultation.

The consultation period began on 25 March 2025 and will run until 25 July 2025. Please ensure that your response reaches us before the closing date.

When responding, please state whether you are responding as an individual or representing the views of an organisation. If responding on behalf of a larger organisation, please make it clear who the organisation represents.

Please note that we do not expect you to submit evidence or views in response to every question listed if not applicable.

If you have any suggestions of others who may wish to be involved in this process, please contact us.

We are aware that in the responses to this CfE there may be commercially sensitive data and information provided. To ensure open and comprehensive returns, we will ensure that responses are treated confidentially and anonymously and commit that no data submitted will be linked to individuals or organisations.

Next steps

A summary of responses, including the next steps, will be published within 3 months of the CfE closing on. Paper copies will be available on request.

If you have questions about this CfE, email: MaritimeVesselsCfE@dft.gov.uk

Call for evidence questions

To respond to the call for evidence, visit the Ways to respond section of the GOV.UK home page for this consultation.

You can respond online by completing the survey or by downloading a Word response form and sending it back via email or post.

The online survey and Word response form will ask you to answer different questions, specific to your area of work. You can see a full list of all the questions in the Word response form.  

Note: we do not expect respondents will answer every question listed below. 

Technology 

Question 1: What type of technological solutions for reducing emissions do you anticipate will be available in the next 5 to 10 years within your sector?

For example, fully electric, electric with an extender, hybrid, zero or near-zero emission fuels (such as green hydrogen), or something else? Alternatively, if it is not possible to use zero or near-zero, emission propulsion technologies, state this and explain why. 

Question 2: Is the technology already available to purchase/use/adopt?  

Question 2.1: If not, when do you estimate that it would be, for example, in the next 2 years, in the next 5 years?  

Question 2.2: If already available, why have you not purchased/used/adopted it already? 

Question 2.3: What are the barriers to expediting the above timelines? Specify the exact barriers and where they apply. 

Question 3: What technological and operational solutions are you considering to reduce your emissions? What factors have influenced this?  

Question 4: Do you agree or disagree with the identified subsectors that have a clear technological pathway for decarbonisation? Explain the reasons for your answer.

Question 5: Do you agree or disagree with the identified subsectors have an unclear technological pathway for decarbonisation? Explain the reasons for your answer.

Capital costs 

Question 6: What are the actual or estimated costs to:

• buy a zero, or near-zero emission vessel and a new, traditionally fuelled vessel?
• buy a second-hand zero, or near-zero, emission vessel and a second-hand traditionally fuelled vessel?
• retrofit a traditionally fuelled vessel to reduce or eliminate emissions?

Operating costs 

Question 7: What are the actual or estimated operating costs of a zero, or near-zero, emission vessel and traditionally fuelled vessel? Provide data from 2023 if available. If unavailable, state the year you are referencing.  

Question 8: What are the top 3 factors that contribute most to overall operational costs? Include answers for both zero or near-zero emission vessels and traditionally fuelled vessels. 

Emissions and fuel consumption 

Question 9: If known, what are the average emissions, both GHG and air pollutants, created by each of your different vessel types across a year?  

If possible, include your responses as tonnes of CO2 equivalent (CO2e) for GHGs. If you do not measure your emissions using this metric, provide your estimates using your alternative preferred metric. Include the methodology used and the rationale for using this metric.  

For air pollutants, provide your emissions in grams per kilowatt hour (g/kWh). 

Provide as much detail as possible on the methodology used in estimating your emissions. 

Question 10: How, if at all, does the ageing of a vessel impact the GHG emissions and air pollutants created, and have you ever retrofitted your vessel to mitigate the GHG emissions and air pollutants created? Provide specific examples.  

Question 11: If known, what is your average fuel consumption per year? Include your responses as tonnes and the specific type of fuel you are referring to. 

Question 12: If you do not monitor your GHG emissions and air pollutants, tell us why and if you intend to start monitoring them? What would make you start monitoring your GHG emissions and air pollutants and are there any barriers preventing this? Do you expect the transition to zero, or near-zero, emission propulsion systems to have any negative wider environmental impacts?

Examples of environmental impacts include, but are not limited to, water quality, biodiversity, climate change adaptation and noise pollution.  

Purchasing and building vessels 

Questions 13 to 15 are for vessel operators and owners.

Question 13: Do you tend to buy vessels new or second hand? What factors do you consider when making this decision? 

Question 14: State which countries your vessels were built in. 

Question 15: What percentage of your fleet will you be able to retrofit with zero or near-zero emission capability?  

• include your vessel type and then number of vessels you are referencing
• what technology/machinery is retrofitted in these cases? 
• what steps have you taken to understand the opportunities and challenges of retrofitting your vessels? 
• what are your estimated time frames for future retrofitting?  
• are you aware of what shipyards are doing outside the UK to maximise their retrofitting capabilities? 

Question 16: When reaching the end of its useful life, how do you dispose of a vessel? Explain whether this is through scrappage or selling and whether this scrappage or selling occurs within or outside the UK.  

Questions 17 to 23 are for shipbuilders.

Question 17: What zero, or near-zero, emission vessels do you have experience in designing and building?  

Question 18: How many zero, or near-zero, emission vessels1 do you currently have on order to build and have built to date? Use data from 2023, or state otherwise.  

• what percentage of your overall output does this reflect? 
• are these vessels for the use in the UK or to be exported? Do you expect this to change over the next 10 years? If yes, indicate why.  

Question 19: What are the typical timeframes for: 

• building new zero, or near-zero, emission vessels? 
• retrofitting existing vessels to emit zero, or near-zero, emissions? 

State if you are referring to bespoke vessels or standardised designs. 

Question 20: How much additional time, if any, would it take to build comparable vessels with zero, or near-zero, emission propulsion technologies compared to vessels with traditional propulsion systems? 

Question 21: What are the barriers you face in building zero, or near-zero, emission vessels? 

Question 22: What changes, if any, are needed at your shipyard to build a greater number of zero, or near-zero, emission vessels? What type of investment is needed?  

Question 23: If you are already building zero, or near-zero, emission vessels, where is the majority of your clean technology supply chain located? Are you aware of what shipyards are doing outside the UK to maximise their retrofitting capabilities? 

Infrastructure 

Question 24: How much fuel or electricity would you require to bunker or charge a zero, or near-zero, emission vessel? 

Question 25: Do you tend to charge/bunker at the same location?  

Question 26: How much choice do you have over where you refuel?  

Question 27: What factors influence where you refuel? How do infrastructure considerations influence investment decisions in reducing emissions? 

Questions 28 to 31 are for ports/harbours/marinas (coastal and inland waterway) shoreside operators.

Question 28: What is the electricity capacity of your operating site currently? Consider the following:

Question 29: What is the capacity for producing and storing zero or near-zero emission fuels at your operating site currently? 

Question 30: What is the additional cost of upgrading your existing infrastructure to support zero, or near-zero emission fuels/energy carriers? 

Question 31: Are you planning to upgrade your capabilities in these areas in the next 5 to 10 years?  

Barriers to switching to zero, or near-zero, emission vessels 

Maritime sector and inland waterways 

Question 32: What are the barriers to switching to zero, or near-zero, emission propulsion systems for specific vessel types? 

Question 33: Have you faced difficulties accessing finance when switching to zero, or near-zero, emission vessels? 

Question 34: What would reduce those barriers (for each vessel type)? 

Regulations and reporting emissions 

Question 35: Are your voyages reported and/or subject to any regulations? If yes, state which regulations.

Question 36: Do you currently report your GHG emissions and air pollutants and to where do you report them?  

Question 37: Detail how you currently calculate your emissions. For some users, this may be calculated through fuel purchase and use. 

Question 38: If you do not report your emissions, estimate the benefits and costs of having to do this in the next 5 to 10 years. 

Question 39: Would you support the introduction of a registration system for sub-sectors that do not currently have one, such as inland waterways or recreational vessels, for supporting decarbonisation goals?  

Exemptions 

Question 40: Are there any specific vessels and/or subsectors that should be exempt from potential future policy which may aim to accelerate the adoption of zero, or near-zero, emission propulsion systems? State your reasons why.

General questions

We are also asking the following general questions of everyone who responds to the call for evidence.

Question 41: what, if any, do you think are the main barriers to accelerating the use of zero or near-zero technologies?

Question 42: Are there any specific vessels and/or subsectors that should be exempt from potential future policy which may aim to accelerate the adoption of zero, or near zero, emission propulsion systems? Please state your reasons why.

Question 43: what, if any, are the 3 environmental impacts that you are most concerned about in the transition to zero emission fuels?

Question 44: do you agree or disagree with our identified subsectors having a clear technological pathway for decarbonisation?

Question 45 : do you agree or disagree with our identified subsectors having an unclear technological pathway for decarbonisation?

Question 46: what, if any, other sub-sectors do you think should be included as having a clear or unclear technological pathway for decarbonisation?

Question 47: do you have any other comments?

Definitions

To ensure comprehensive data gathering and informed policy development, it is essential to for industry and government to work from the same definitions.

Vessels

For the purpose of this CfE we will define a vessel to mean any watercraft designed for transportation or other purposes on water. More information on vessel classification and certification.

Domestic journeys

All journeys taken on inland waters are considered domestic. Domestic journeys also include all shipping between:

• Two UK ports, harbours, and marinas
• a UK port, harbour or marina and an offshore installation, for example, a domestic oil rig

Inland waterways

Inland waterways include any area of water not categorised as ‘sea’. This includes: - rivers - canals - estuaries - lakes - lochs

More information on categorisation of inland waterways.

GHGs

The emissions accounted for under the GHG protocol are the 7 gases covered by the Kyoto protocol:

• carbon dioxide (CO2)
• methane (CH4)
• nitrous oxide (N2O)
• hydrofluorocarbons (HFCs)
• perfluorocarbons (PFCs)
• sulphur hexafluoride (SF6)
• nitrogen trifluoride (NF3)

Air pollutants

Air pollutants most relevant to the maritime sector include but are not limited to:

• particulate matter (PM2.5 and PM10)
• ozone (O3)
• nitrogen oxides (NOx)
• sulphur dioxide (SO2)
• non-methane volatile organic compounds (NMVOC)
• ammonia (NH3)

Wider environmental impacts

For this CfE, we have defined wider environmental impacts to cover activities that will affect living organisms, their habitats, land, air and water, as well as wider natural processes, systems and cycles and the need to consider climate change adaptation.

See the Environment principles policy statement for more information on wider environmental impacts.

Emissions

This CfE accompanies the maritime decarbonisation strategy, the primary objective of which is to meet GHG emission reduction targets.

Therefore, when we refer to ‘emissions’ within this CfE we are referring to GHG emissions as referenced above, unless explicitly stated.

Freedom of Information

Information provided in response to this consultation, including personal information, may be subject to publication or disclosure in accordance with the Freedom of Information Act 2000 (FOIA) or the Environmental Information Regulations 2004.

If you want information that you provide to be treated as confidential, please be aware that, under the FOIA, there is a statutory Code of Practice with which public authorities must comply and which deals, amongst other things, with obligations of confidence.

In view of this it would be helpful if you could explain to us why you regard the information you have provided as confidential. If we receive a request for disclosure of the information, we will take full account of your explanation, but we cannot give an assurance that confidentiality can be maintained in all circumstances. An automatic confidentiality disclaimer generated by your IT system will not, of itself, be regarded as binding on the Department.

The Department will process your personal data in accordance with the Data Protection Act (DPA) and in the majority of circumstances this will mean that your personal data will not be disclosed to third parties.

Data Protection

DfT is carrying out this CfE to gather evidence on Emission reduction measures for for  smaller vessels and targeted subsectors. This CfE and the processing of personal data that it entails is necessary for the exercise of our functions as a government department. If your answers contain any information that allows you to be identified, DfT will, under data protection law, be the Controller for this information.

As part of the CfE process, we are asking for your name and email address. This is in case we need to ask you follow-up questions about any of your responses. You do not have to give us this personal information. If you do provide it, we will use it only for the purpose of asking follow-up questions.

DfT’s privacy policy has more information about your rights in relation to your personal data, how to complain and how to contact the Data Protection Officer.

Your information will be kept securely on a secure IT system within the department and destroyed within 12 months after the CfE process has been completed.

1. Emissions figures on a tank to wake (TtW) basis including emissions from inland waterway and leisure vessels, from DfT maritime emissions model ↩

2. Energy and environment: data tables ↩

3. A vessel equipped with a mounted light and moored at a place dangerous to navigation. ↩