Techno-Economic Analysis of Multi-Purpose Heavy-Lift Vessels Using Methanol as Fuel

Abstract

With the global maritime industry accelerating toward carbon neutrality, the adoption of alternative marine fuels has emerged as a pivotal pathway for achieving net-zero emissions. To identify the most promising fuel transition solution for multi-purpose heavy-lift vessels (MPHLVs), which are widely used for transporting large and complex industrial equipment and have specialized structural requirements, this study conducted a comprehensive techno-economic analysis based on a fleet of 12 MPHLVs. An eight-dimensional technical adaptability framework was established, and six types of marine fuel were evaluated. Concurrently, a total cost assessment model was developed using 2024 operational data of the fleet, incorporating the fuel procurement, the carbon allowances under the EU ETS, the FuelEU Maritime compliance costs, and the IMO Net-Zero penalties. The results show that methanol as an alternative fuel is the most compatible decarbonization pathway for this specialized vessel type. A case study of a 38,000 DWT methanol-fueled MPHLV further demonstrates engineering feasibility with minimal impact on cargo capacity, and validates methanol’s potential as a technically viable and strategically transitional fuel for MPHLVs, particularly in the context of stricter international decarbonization regulations. The proposed evaluation framework and engineering application offer practical guidance for fuel selection, ship design, and retrofit planning, supporting the broader goal of accelerating low-carbon development in heavy-lift shipping sector.

1. Introduction

1.1. Background

The shipping industry remains the cornerstone of global trade, transporting approximately 90% of international cargo [1]. However, this sector remains highly dependent on fossil fuels, annually accounting for approximately 3% of the global greenhouse gas (GHG) emissions [2]. According to the World Bank, if the maritime industry were a nation, it would rank as the sixth-largest emitter globally, surpassing Japan and trailing Germany [3]. As the global economy transitions toward green and low-carbon development [4], the decarbonization of maritime transportation has significantly lagged behind that of other sectors [5]. A critical challenge resides in the limited commercial competitiveness of alternative marine fuels. Due to their higher production costs and lower energy densities, the effective cost per transport unit for alternative fuels can exceed that of conventional fuels by a factor of three [6]. Therefore, technological advancement alone is insufficient to drive the sector’s green transition. Instead, coordinated regulatory mechanisms and economic instruments are essential to enable a structured transformation within a unified global framework.

In the meantime, with the development and expansion of modern industry, including wind power, industrial modules, rail transit, and energy infrastructure, the demands for transporting large, heavy, and irregular cargo are increasing as well [7]. Conventional bulk carriers and container ships often struggle to meet these specialized requirements, especially with regard to deck strength, cargo hold flexibility, and onboard lifting capacity. In this context, multi-purpose heavy-lift vessels (MPHLVs) have grown increasingly important in the modern shipping industry, particularly in response to the global demand for complex logistics solutions [8]. MPHLVs, equipped with high-strength deck structures, reconfigurable cargo holds, and heavy-lift cranes, have become indispensable in heavy cargo logistics and specialized transport operations. Against the backdrop of green transformation in shipping and the application of alternative fuels, research on low-carbon fuel solutions for MPHLVs is particularly significant for supporting the green transformation of these high-value ships.

1.2. Literature Review

The European Union (EU) has taken a leading role by integrating maritime emissions into the EU Emissions Trading System (EU ETS) [9,10], which entered into force from 1 January 2024. The system applies to all commercial cargo and passenger vessels over 5000 gross tons and covers 50% of emissions on voyages between EU and non-EU ports, and 100% of emissions on intra-EU voyages and during berthing [9,11]. Shipping operators must comply with the revised Monitoring, Reporting, and Verification (MRV) regulations [12], which will incorporate methane (CH₄) and nitrous oxide (N₂O) into the EU ETS system starting from 2026. During a two-year transition period, only 40% and 70% of verified CO₂ emissions will be taxed in 2024 and 2025, respectively. Complementing this initiative, the FuelEU Maritime regulation entered into force in 2025, establishing a progressive reduction in GHG intensity standards for marine fuels across their full lifecycle [13]. The regulation imposes financial penalties for exceeding the annual baseline GHG intensity and mandates the use of onshore power supply (OPS) or zero-emission technologies during berthing [14]. The gradually tightening GHG intensity targets and rising penalties are designed to accelerate the adoption of low- and zero-carbon fuels [15].

At the global level, the International Maritime Organization (IMO) adopted a draft amendment to MARPOL Annex VI during the 83rd session of Marine Environment Protection Committee (MEPC) from 7 to 11 April 2025, approving the “IMO Net-Zero Framework” [16]. This regulatory framework represents the world’s first dual-track system combining mandatory emissions limits with a GHG pricing mechanism, targeting net-zero GHG emissions for international shipping by or around 2050. The framework mandates progressive reductions in GHG fuel intensity (GFI) [17,18], measured on a well-to-wake (WTW) basis, and introduces economic instruments such as remedial units to offset excess emissions and incentives for ships adopting zero- or near-zero-emission technologies [19,20]. These regulations will apply to ocean-going vessels over 5000 GT, which account for approximately 85% of total maritime CO₂ emissions, and are expected to be enforced starting in 2028.

In response to global regulatory trends and technological advancements, many newly built vessels, especially in the container and tanker segments, have embraced low-carbon alternative fuels such as LNG [21,22] and methanol [23]. Each fuel option, such as LNG, methanol, ammonia, hydrogen, and bio-fuels, presents distinct advantages and challenges [24]. LNG, the most commercially mature alternative fuel [25], is supported by the established infrastructure and is widely used in various ship types [26]. Nevertheless, it remains a fossil fuel, and its long-term decarbonization potential is limited. Ammonia and hydrogen are recognized as key zero-carbon fuels for the future, but their toxicity, storage complexity, and system immaturity limit their near-term viability [27]. Lifecycle carbon-neutral bio-fuels face uncertainties in supply, cost, and standardization [28]. Methanol, conversely, offers clean combustion, liquid-state storage, relatively straightforward retrofitting, and an increasingly mature production and distribution network [29]. The adoption of green methanol further enhances its long-term appeal as a scalable maritime fuel, including for application in MPHLVs. A comparative overview of key alternative fuels for shipping decarbonization is summarized in

Table 1. Comparative overview of key alternative fuels for ships [30,31,32].

Fuel Type	Carbon Reduction Potential	Technology Maturity	Storage Conditions	Volumetric Energy Density (GJ/m3)	Key Challenges
LNG	20–30% CO2 reduction	High	Cryogenic storage at −162 °C or high-pressure tanks	20.8–24.8	Methane slip; fossil-based; limited long-term potential
Green Methanol	83–94% CO2 reduction (WTW)	Medium	Liquid storage at ambient temperature and pressure	15.8	Immature supply chain; higher cost than fossil fuels
Ammonia	Zero Carbon (CO2-free combustion)	Low	Low-temperature storage; highly volatile	12.6	High toxicity; safety and regulatory issues unresolved
Hydrogen	Zero Carbon	Low	−253 °C cryogenic or high-pressure storage	4.5–8.5	Very low density; high storage volume and cost
Bio-fuels	Low carbon	Medium to High	Conventional liquid storage	33–38	Limited feedstock availability; cost and sustainability

, highlighting differences in carbon reduction potential, energy density, and technology readiness.

With increasingly stringent global regulations on maritime GHG emissions, the development and selection of alternative marine fuels has become a prominent focus in green shipping research. The choice of alternative fuel is not only a technical decision but also involves multi-dimensional considerations including economic viability, sustainability, regulatory compliance, and operational feasibility. Accordingly, techno-economic analysis (TEA) has emerged as a key methodology for evaluating the suitability of alternative fuel pathways in the maritime sector [33,34]. TEA enables the establishment of integrated system models that incorporate technical factors such as fuel adaptability, energy efficiency, engine compatibility, and retrofitting feasibility, as well as economic elements including capital expenditures (CAPEX), operational expenditures (OPEX), maintenance costs, fuel price volatility, and carbon allowances [35]. This comprehensive framework allows for the quantitative comparison of multiple fuel options under consistent criteria, supporting both technical feasibility assessments and long-term economic competitiveness forecasting.

Recent studies have widely applied TEA to evaluate various alternative fuels such as LNG, methanol, ammonia, hydrogen, and bio-fuels across different vessel types [36,37,38]. Some focus on retrofitting costs and performance for specific ship classes (e.g., tankers, container ships, Ro-Ro vessels), while others combine TEA with policy-driven sensitivity analysis under emerging regulations, such as IMO’s Carbon Intensity Indicator (CII) and the EU ETS, to project future economic viability and regulatory adaptability [39]. TEA has proven to be a robust tool for supporting ship fuel transition strategies by enabling multi-criterion decision-making that integrates environmental, technical, and economic dimensions. For complex and flexible vessels such as MPHLVs, TEA is particularly valuable in evaluating methanol fuel adoption, as it allows for scenario-based assessments across diverse operational profiles and policy frameworks.

MPHLVs are hybrid ship types that integrate the functionality of general cargo ships and heavy-lift carriers. They are capable of transporting bulk cargo, containers, and oversized engineering components such as industrial modules and wind turbine components. In classification terms, MPHLVs are typically registered under general cargo or general cargo/container ship categories, evolving from traditional dry cargo ships since the 1990s to fulfill increasingly specialized logistics demands. With the tightening of maritime environmental regulations, the design and classification of MPHLVs have been re-examined. The IMO Energy Efficiency Design Index (EEDI), Energy Efficiency Existing Ship Index (EEXI), and Carbon Intensity Indicator (CII) were introduced to promote fuel efficiency and emission control [40]. However, due to their operational characteristics—frequently operating at full volume but not full load—the International Association of Classification Societies (IACS) clarified in Document No. 170 (May 2022) that heavy-lift carriers may be exempt from EEDI, EEXI, and CII requirements under certain conditions as defined in MARPOL Annex VI [41]. MPHLVs, which are fulfilling the adapted criterion of “ships engaged in lifting operations” as per 2008 IMO IS Code (as amended by MSC.443(99)) [42], are characterized as follows:

SWL × Outreach ≥ 0.67 × Displacement × (D − T)/B

(1)

where SWL is the maximum safe working load of crane of one single crane; Outreach is outreach from the turning axis of crane; Displacement is the displacement of the vessel at draft T; T is the freeboard draft; B is the molded breadth of the vessel measured amidships at draft T; D is the depth for freeboard.

In recent years, MPHLVs in service have applied to their respective flag states to reclassify their vessel type from general dry cargo ships to heavy cargo carriers. This trend reflects a growing need to align vessel registration with operational characteristics and regulatory exemptions under IMO environmental frameworks. Nevertheless, the term MPHLV continues to be widely adopted across the industry due to its ability to concisely capture the vessel’s hybrid functional and structural capabilities. To support this study, a dataset from typical MPHLVs of varying deadweight tonnage (DWT), including both existing ships and those currently under construction, was compiled. Based on statistics of the global fleet, two DWT ranges, 10,000~15,000 DWT and 20,000~40,000 DWT, were identified as the main capacity groups. Based on this, three typical vessels were selected, along with the currently largest MPHLV in operation (62,000 DWT), to provide a diverse basis for comparison and analysis. Their key technical parameters are summarized in

Table 2. Parameters for typical MPHLVs at present.

Ship Parameter	12,500 DWT	13,000 DWT	14,000 DWT	22,000 DWT	32,000 DWT	38,000 DWT	62,000 DWT
Year of initial order	2014	2015	2024	2025	2022	2023	2020
Overall length (m)	147	149.99	159.75	165	179.9	182.0	199.9
Molded breadth (m)	22.8	25.6	22.8	25.6	30.0	30.0	32.26
Molded depth (m)	11.55	10.65	11.55	13.5	15.5	16.0	19.3
Service speed (knots)	15.3	15.3	15.0	14.0	14.5	14.5	14.4
Crane configuration	2 × 250 t	2 × 450 t	2 × 250 t	2 × 150 t 1 × 100 t	3 × 350 t	2 × 400 t 1 × 200 t	2 × 150 t 2 × 80 t
Cargo hold volume (m3)	17,600	26,600	20,100	28,000	40,000	44,000	74,800
Longest cargo hold length (m)	76.5	105.45	89.25	79.5	68.4	52.8	39.36
Endurance range (nm)	10,200	12,000	11,000	10,000	18,000	15,000	18,000
Fuel type	LFO	LFO	Methanol ready	Methanol ready	Methanol ready	LFO	LFO
Bridge location	Stern	Bow	Stern	Stern	Bow	Bow	Stern

.

1.3. Challenges and Research Gaps

Based on the current status and development trends of mainstream MPHLVs, the following key ship-type characteristics can be summarized:

(a) Moderate vessel size: MPHLVs are typically under 40,000 DWT, with lengths below 200 m and beams not exceeding 32.3 m. This reflects the specialized but limited demand for break bulk and engineering components, which is different from the mainstream bulk or containerized trade.

(b) Reinforced cargo holds with wide openings: The cargo deck is designed to bear more than 20 t/m², and features box-shaped holds with adjustable tweendecks to enhance load flexibility. Hold segmentation is minimized to maximize the loading of long or irregular cargo.

(c) Flat open-deck stowage area: A defining feature is the open-air stowage area atop the hatch covers. Bridge superstructures are located forward, and cranes are installed on a single side to create an unobstructed rectangular deck space suitable for oversized cargo.

Given the small tonnage of MPHLVs and the industry trend toward forward-positioned bridges, the high demand for unobstructed cargo hold and deck loading areas presents significant challenges in the arrangement of fuel storage tanks or cylindrical tanks. For example, installing LNG tanks in hold spaces would reduce cargo capacity, while placing them on deck interferes with stowage of long components. Moreover, the total cost of adopting different fuels is no longer limited to procurement expenses alone, yet there remains a lack of comprehensive models for holistically evaluating the full lifecycle costs of alternative marine fuels, including emissions costs. The lack of dedicated green propulsion solutions for MPHLVs has become a critical engineering gap in the shipping industry’s green fuel transition.

1.4. Objectives and Innovations

This study aims to evaluate the technical and economic feasibility of adopting methanol-fueled power systems in MPHLVs. By focusing on this complex and high-flexibility ship type, the study investigates the fuel system configuration, design constraints, and cost trade-offs associated with methanol application. The main contributions of this study are summarized as follows:

(a) A targeted techno-economic investigation is conducted for the MPHLVs, ad-dressing a gap in the literature and supporting the IMO 2050 decarbonization goals;

(b) A comprehensive evaluation framework is proposed, integrating technical compatibility, policy compliance, and lifecycle cost modeling to support alternative fuel selection;

(c) A comparative analysis is performed using real operational data from a representative vessel fleet, quantifying the total annual cost and emission performance of different fuel options;

(d) A practical methanol-fueled propulsion configuration is designed for a newly built 38,000 DWT MPHLV, providing engineering insights and reference for future vessel development.

2. Methodology

For the issue of fuel transition in MPHLVs, it is necessary to comprehensively consider both technical compatibility and economic feasibility of fuel usage. The comprehensive evaluation method, also known as the comprehensive assessment method or multi-criterion comprehensive evaluation method, is adopted for technical compatibility. This refers to a systematic and standardized approach for evaluating multiple indicators and factors simultaneously. A total cost calculation model for various fuel usage is developed by incorporating the existing and future decarbonization regulations in shipping (e.g., carbon allowances) as additional cost calculation methods related to fuel consumption. Based on the research content of these two methods, an appropriate heavy-lift vessel fleet is selected to collect relevant data.

2.1. Technical Analysis Methods

To systematically evaluate the technical adaptability of various alternative fuels, including methanol, ammonia, LNG, bio-fuels, and hydrogen, for use in MPHLVs, a comprehensive evaluation method was adopted to construct a multi-dimensional technical assessment system. Based on the technical factors that need to be considered in the design and operation of MPHLVs when switching marine fuels for new building, eight technical evaluation dimensions were identified. Different weights were assigned to each dimension, with each 1% of weight equivalent to 1 point in the scoring system. Using conventional fuels as a benchmark (assigned full marks across all eight technical evaluation dimensions), other fuels were comparatively assessed. The Delphi method was employed, where multiple experts provided independent scores, and the average value was taken as the final score for each dimension. The study engaged a panel of experts, including ship designers, shipbuilders, classification society surveyors, and operators/managers of MPHLVs, to conduct multi-perspective technical evaluations. The composite score for each fuel was calculated by summing the weighted scores across all dimensions. This final score enables comparative analysis of the technical compatibility for different fuels for this specific vessel type. The evaluation dimensions, weight distribution, and criteria are detailed in

Table 3. Multi-criterion scoring framework for evaluating the technical adaptability of alternative marine fuels in MPHLVs.

Assessment Dimension	Indicator Description	Weight (%)	Evaluation Methodology
Storage adaptability	Fuel energy density (liquid/gas), temperature/pressure conditions, and tank arrangement flexibility	15	FMEA analysis; dimensional comparison with conventional tank layouts
Engine technology maturity	Readiness of engine systems for the target fuel and OEM support availability	15	Scoring based on market availability and operational case studies
Cargo capacity utilization	Volume loss due to fuel storage systems relative to total cargo space	15	Ratio analysis between tank volume and usable deck/hold volume
Range capability	Cruising range determined by volumetric energy content and onboard tank size	10	Scenario simulation based on voyage profiles and fuel properties
Cargo loading flexibility	Impacts of fuel system layout on cargo hold and deck loading patterns	15	CAD-based spatial interference and layout analysis
Port compatibility	Availability of bunkering infrastructure and port acceptance worldwide	10	Database query of bunkering ports and regional distribution analysis
Fuel supply chain stability	Reliability of feedstock supply and price volatility risks	10	Energy economics analysis; market forecast review
Safety and regulatory compliance	Conformity with IMO, class society, and flag state safety and regulatory standards	10	IGF Code compliance review and classification society documentation check

.

2.2. Economic Analysis Methods

To assess the economic viability of different alternative fuels in MPHLVs, a cost accounting model was developed that includes both direct fuel procurement costs and indirect emissions-related expenses. In the context of maritime decarbonization, total fuel cost is no longer limited to purchase price alone; it must also reflect GHG emission penalties and carbon allowance obligations. These costs are dynamic and vary with fuel type, policy changes, and market fluctuations.

The total operating cost of marine fuels is thus a multi-factor variable that can be decomposed into the following components (without considering the interest rate factor):

(a)

Annual Fuel Procurement Cost

The base cost is the annual expenditure on fuel, expressed in USD, is:

$${\mathrm{C}}_{\mathrm{f}\mathrm{u}\mathrm{e}\mathrm{l}}={\mathrm{Q}}_{\mathrm{f}\mathrm{u}\mathrm{e}\mathrm{l}}\times {\mathrm{P}}_{\mathrm{f}\mathrm{u}\mathrm{e}\mathrm{l}}$$

(2)

where Q_fuel is the total fuel consumption per year, t; P_fuel is the average annual price of fuel, USD/t.

(b)

Carbon allowances Under the EU ETS (Until 2027)

From 2024 onward, ships operating in EU/EEA (European Economic Area) regions are subject to carbon allowances [9], based on their verified CO₂ emissions as Equation (3) in EUR:

$${\mathrm{C}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}\mathrm{o}\mathrm{n} \mathrm{a}\mathrm{l}\mathrm{l}\mathrm{o}\mathrm{w}\mathrm{a}\mathrm{n}\mathrm{c}\mathrm{e}}={\sum }_{\mathrm{i}}({\mathrm{Q}}_{\mathrm{f}\mathrm{u}\mathrm{e}\mathrm{l},\mathrm{E}\mathrm{U}}\times {\mathrm{C}}_{\mathrm{F}})\times {\mathrm{P}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}\mathrm{o}\mathrm{n}}$$

(3)

where C_F is the carbon emission conversion factor defined by IMO for each fuel, tCO₂/t-fuel; P_carbon is the EU ETS carbon price, EUR/tCO₂; Q_fuel,EU is the fuel amount used in the EU/EEA, t.

(c)

FuelEU Maritime GHG Intensity Penalties (From 2025)

The FuelEU Maritime regulation requires compliance with annual GHG intensity baselines [13]. If exceeded, a penalty is calculated as Equation (4); the unit is EUR.

$${\mathrm{C}}_{\mathrm{F}\mathrm{u}\mathrm{e}\mathrm{l}\mathrm{E}\mathrm{U}\mathrm{P}\mathrm{e}\mathrm{n}\mathrm{a}\mathrm{l}\mathrm{t}\mathrm{y}}={\displaystyle \frac{\left|\mathrm{C}\mathrm{o}\mathrm{m}\mathrm{p}\mathrm{l}\mathrm{i}\mathrm{a}\mathrm{n}\mathrm{c}\mathrm{e} \mathrm{b}\mathrm{a}\mathrm{l}\mathrm{a}\mathrm{n}\mathrm{c}\mathrm{e}\right|}{{\mathrm{G}\mathrm{H}\mathrm{G}\mathrm{I}\mathrm{E}}_{\mathrm{a}\mathrm{c}\mathrm{t}\mathrm{u}\mathrm{a}\mathrm{l}}\times 41000}}\times 2400$$

(4)

where GHGIE_actual is the actual annual GHG intensity of the energy used onboard a ship, calculated for the relevant reporting period, gCO₂eq/MJ; 41,000 is the energy equivalent of 1 t VLSFO (Very Low Sulfur Fuel Oil), MJ; 2400 is the unit penalty per t VLSFO equivalent, EUR.

The compliance balance is calculated as Equation (5) [13]:

$$\mathrm{C}\mathrm{o}\mathrm{m}\mathrm{p}\mathrm{l}\mathrm{i}\mathrm{a}\mathrm{n}\mathrm{c}\mathrm{e} \mathrm{b}\mathrm{a}\mathrm{l}\mathrm{a}\mathrm{n}\mathrm{c}\mathrm{e}=\left({\mathrm{G}\mathrm{H}\mathrm{G}\mathrm{I}\mathrm{E}}_{\mathrm{t}\mathrm{a}\mathrm{r}\mathrm{g}\mathrm{e}\mathrm{t}}-{\mathrm{G}\mathrm{H}\mathrm{G}\mathrm{I}\mathrm{E}}_{\mathrm{a}\mathrm{c}\mathrm{t}\mathrm{u}\mathrm{a}\mathrm{l}}\right)\times ({\sum }_{\mathrm{i}}^{\mathrm{n}}{\mathrm{M}}_{\mathrm{i}}\times {\mathrm{L}\mathrm{C}\mathrm{V}}_{\mathrm{i}}+{\sum }_{\mathrm{k}}^{\mathrm{c}}{\mathrm{E}}_{\mathrm{k}})$$

(5)

where Compliance balance is the grams of CO₂ equivalent, gCO_2eq; GHGIE_target is the annual GHG intensity limit provided by EU; i is the index corresponding to the fuel types delivered to the ship in the reporting period; n is the total number of fuel types delivered to the ship in the reporting period; k is the index corresponding to the Onshore Power Supply (OPS) connection points; c is the total number of OPS connection points; M_i is the mass of fuel i consumed in EU/EEA, gFuel; LCV_i is the lower calorific value of fuel i, MJ/gFuel; E_k is the electricity delivered to the ship per OPS connection point, MJ.

Ships that have a higher GHG intensity than the requirement must pay a penalty corresponding to its compliance deficit as per Equation (4). If a ship has an average GHG intensity below the requirement, the compliance surplus can be banked for use in the subsequent compliance period, or be pooled for other ships.

(d)

IMO Net-Zero Framework Compliance Costs (From 2028)

Once the IMO Net-Zero Framework is implemented (targeted for 2028), compliance costs in USD will be governed by GHG Fuel Intensity (GFI) targets, specifically, the Base Compliance Target (BCT) and Direct Compliance Target (DCT) [16].

Tier 1 Penalty (GFI exceeds DCT but below BCT):

$${\mathrm{C}}_{\mathrm{T}\mathrm{i}\mathrm{e}\mathrm{r} 1 \mathrm{R}\mathrm{U}\mathrm{s}}=\left({\mathrm{G}\mathrm{F}\mathrm{I}}_{\mathrm{a}\mathrm{c}\mathrm{t}\mathrm{u}\mathrm{a}\mathrm{l}}-{\mathrm{G}\mathrm{F}\mathrm{I}}_{\mathrm{D}\mathrm{C}\mathrm{T}}\right)\times \left({\mathrm{Q}}_{\mathrm{f}\mathrm{u}\mathrm{e}\mathrm{l}}\times {\mathrm{L}\mathrm{C}\mathrm{V}}_{\mathrm{i}}\right)\times {\displaystyle \frac{100}{1000}}$$

(6)

Tier 2 Penalty (GFI exceeds BCT):

$${\mathrm{C}}_{\mathrm{T}\mathrm{i}\mathrm{e}\mathrm{r} 2 \mathrm{R}\mathrm{U}\mathrm{s}}=\left({\mathrm{G}\mathrm{F}\mathrm{I}}_{\mathrm{a}\mathrm{c}\mathrm{t}\mathrm{u}\mathrm{a}\mathrm{l}}-{\mathrm{G}\mathrm{F}\mathrm{I}}_{\mathrm{B}\mathrm{C}\mathrm{T}}\right)\times \left({\mathrm{Q}}_{\mathrm{f}\mathrm{u}\mathrm{e}\mathrm{l}}\times {\mathrm{L}\mathrm{C}\mathrm{V}}_{\mathrm{i}}\right)\times {\displaystyle \frac{100}{1000}}$$

(7)

Additional Tier 1 Penalty (gap between BCT and DCT):

$${\mathrm{C}}_{\mathrm{T}\mathrm{i}\mathrm{e}\mathrm{r} 1 \mathrm{R}\mathrm{U}\mathrm{s}}^{\prime }=\left({\mathrm{G}\mathrm{F}\mathrm{I}}_{\mathrm{B}\mathrm{C}\mathrm{T}}-{\mathrm{G}\mathrm{F}\mathrm{I}}_{\mathrm{D}\mathrm{C}\mathrm{T}}\right)\times \left({\mathrm{Q}}_{\mathrm{f}\mathrm{u}\mathrm{e}\mathrm{l}}\times {\mathrm{L}\mathrm{C}\mathrm{V}}_{\mathrm{i}}\right)\times {\displaystyle \frac{100}{1000}}$$

(8)

where GFI_actual is the GHG Fuel Intensity actual, tCO_2eq/MJ; GFI_BCT is the GHG Fuel Intensity Base Compliance Target, tCO_2eq/MJ; GFI_DCT is the GHG Fuel Intensity Direct Compliance Target, tCO_2eq/MJ; 100 means 100 USD per ton of CO_2eq in Tier 1 RUs; 380 means 380 USD per ton of CO_2eq in Tier 2 RUs; 1000 means 1 GJ = 1000 MJ.

(e)

Total Cost Calculation

The total cost depends on which emission control framework is active.

Before 2028 (EU ETS + FuelEU):

$${\mathrm{C}}_{\mathrm{t}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{l}}={\mathrm{C}}_{\mathrm{f}\mathrm{u}\mathrm{e}\mathrm{l}}+({\mathrm{C}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}\mathrm{o}\mathrm{n}\mathrm{a}\mathrm{l}\mathrm{l}\mathrm{o}\mathrm{w}\mathrm{a}\mathrm{n}\mathrm{c}\mathrm{e}}+{\mathrm{C}}_{\mathrm{F}\mathrm{u}\mathrm{e}\mathrm{l}\mathrm{E}\mathrm{U}\mathrm{P}\mathrm{e}\mathrm{n}\mathrm{a}\mathrm{l}\mathrm{t}\mathrm{y}})\times 1.08$$

(9)

When the IMO Net-Zero Framework is officially implemented in 2028 as scheduled, its emission reduction targets are expected to be more stringent and comprehensive than those established under the FuelEU Maritime regulation, as illustrated in Figure 1. In addition to tighter GHG intensity limits, the IMO framework will likely apply on a global scale, extending beyond the regional scope of EU measures.

Industrial consensus suggests that, once in force, the IMO Net-Zero Framework will effectively supersede the existing EU regulations, namely, the EU ETS carbon pricing scheme and the FuelEU Maritime compliance system. As such, this study assumes that after 2028, only the IMO Net-Zero Framework will remain in effect for emission compliance and cost calculation. Accordingly, the total fuel cost model post 2028 is categorized into three distinct scenarios, depending on whether the GHG Fuel Intensity (GFI) of a ship’s fuel use complies with the designated annual targets [16]. The cost calculation methodology under each scenario is described below.

After 2028 (IMO Net-Zero only):

If GFI_actual > GFI_BCT

$${\mathrm{C}}_{\mathrm{t}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{l}}={\mathrm{C}}_{\mathrm{f}\mathrm{u}\mathrm{e}\mathrm{l}}+{\mathrm{C}}_{\mathrm{T}\mathrm{i}\mathrm{e}\mathrm{r} 2 \mathrm{R}\mathrm{U}\mathrm{s}}+{\mathrm{C}}_{\mathrm{T}\mathrm{i}\mathrm{e}\mathrm{r} 1 \mathrm{R}\mathrm{U}\mathrm{s}}^{\prime }$$

(10)

If GFI_DCT < GFI_actual ≤ GFI_BCT

$${\mathrm{C}}_{\mathrm{t}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{l}}={\mathrm{C}}_{\mathrm{f}\mathrm{u}\mathrm{e}\mathrm{l}}+{\mathrm{C}}_{\mathrm{T}\mathrm{i}\mathrm{e}\mathrm{r} 1 \mathrm{R}\mathrm{U}\mathrm{s}}$$

(11)

If GFI_actual < GFI_DCT

$${\mathrm{C}}_{\mathrm{t}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{l}}={\mathrm{C}}_{\mathrm{f}\mathrm{u}\mathrm{e}\mathrm{l}}-{\mathrm{C}}_{\mathrm{T}\mathrm{i}\mathrm{e}\mathrm{r}1\mathrm{R}\mathrm{U}\mathrm{s}}$$

(12)

In the last case, the ship receives Surplus Units (SUs), which can be used to offset future GFI deficits or traded in the emission credit market.

2.3. Data Sources and Processing Methods

This study utilizes operational and technical data obtained from a fleet of 12 MPHLVs, and four new design vessels with a planned DWT of 38,000 tons. These vessels represent a wide range of mainstream MPHLV designs currently active in the global shipping market. The fleet’s diversity in terms of size, operational mode, propulsion systems, energy use patterns, and carbon emission profiles ensures the representativeness and reliability of the dataset. This fleet-level data forms a robust foundation for conducting both the technical adaptability assessment and the economic evaluation of methanol-fueled retrofit or new design options.

2.3.1. Data Sources

The data spans the full calendar year of 2024 and is categorized into two primary types:

Technical configuration data: Includes each vessel’s main engine specifications, fuel tank design and layout, auxiliary power systems, electrical generation architecture, hull arrangement, service life, maintenance intervals, and onboard fuel management strategies.

Carbon emission and fuel usage data: Derived from established reporting systems such as the Ship Energy Efficiency Management Plan (SEEMP), Records of Fuel Oil Consumption (ROC), Monitoring, Reporting and Verification (MRV) submissions, and the Energy Efficiency Operational Indicator (EEOI). These sources were used to compute total annual fuel consumption, regional fuel use within the EU/EEA, and overall GHG emissions.

As a result, the economic analysis focuses on 12 ships.

Table 4. Annual operational data of selected MPHLVs used for techno-economic analysis (year 2024).

DWT (t)	Distance (nm)	HFO (t)	LSFO (t)	MGO (t)	Total CO2 Emission (t)	Total Fuel Consumption (t-eq)	CO2 Emission in EU (t)	Fuel Consumption in EU (t-eq)
30,000	57,469	4520.07	150.00	802.38	17,121	5498	7987	2565
30,000	54,953	2857.60	1526.70	1172.07	17,467	5609	4217	1354
30,000	68,437	4321.30	897.28	629.30	18,301	5877	6155	1977
30,000	53,919	3482.87	1335.80	914.74	17,987	5776	6708	2154
30,000	52,782	3913.10	300.00	891.17	15,988	5134	5347	1717
30,000	79,751	4266.26	1350.51	640.27	19,593	6292	3534	1135
30,000	63,144	5154.65	0.00	1171.37	19,807	6361	8923	2865
32,000	68,658	4203.03	1175.92	834.97	19,470	6253	7324	2352
32,000	65,424	5884.74	233.40	1081.16	22,527	7234	4217	1354
32,000	66,584	4065.23	629.90	833.87	17,317	5561	7541	2422
32,000	63,717	5040.72	0.00	525.96	17,383	5582	4778	1534
32,000	72,568	5405.69	667.30	230.50	19,675	6318	5753	1847
Average						5958	-	1940

presents the 2024 operational data of 12 representative MPHLVs used in the analysis, including voyage distance, fuel breakdown, and CO₂ emissions inside EU/EEA. The average annual equivalent fuel consumption per vessel is approximately 5958 t, including 1940 t in the EU/EEA.

2.3.2. Data Processing Methods

The raw dataset was first cleaned and pre-processed to ensure consistency and reliability. This included the removal of outliers and incomplete records, normalization of time series, and unification of measurement units across all ships. Subsequently, statistical analysis was applied to summarize the operational characteristics of the fleet, which was further classified and grouped based on ship-type features such as length, beam, and DWT and technical parameters such as engine output, energy efficiency, and fuel tank utilization. To support the subsequent technical evaluation and construction of the multi-dimensional scoring model, three categories of core indicators were extracted from the processed dataset:

(a) Tank capacity and loading flexibility indicators: These reflect the feasibility of integrating alternative fuel storage systems without significantly compromising cargo layout.

(b) Fuel consumption and route efficiency indicators: These influence baseline carbon emission calculations and support comparative analysis of GHG intensity under different fuels.

(c) Engine technology maturity and system adaptability indicators: These determine the level of complexity and integration difficulty associated with methanol fuel system retrofits or installations.

Finally, the fleet serves as a real-world case study for implementing a dynamic, engineering-based techno-economic evaluation framework. This enables a holistic and evidence-based demonstration of the feasibility of methanol-fueled propulsion in the context of new design MPHLVs.

3. Results and Discussion

3.1. Technical Analysis Results

Based on the operational characteristics and long-term data collected from a fleet of 12 MPHLVs, a comprehensive technical adaptability assessment of five alternative marine fuels compared with conventional fuel oil was conducted. The evaluation considered multiple dimensions, including fuel storage requirements, power system maturity, integration feasibility, and market readiness.

Using the methodology described in Section 2.1 and the data processing framework outlined in Section 2.3, a multi-dimensional scoring model was applied to quantify the technical compatibility of each fuel type with the specific design and operational features of MPHLVs. Each fuel was scored across eight weighted criteria (see Table 3), and the total scores reflect the relative adaptability of each fuel under current technological and regulatory conditions. The results of the technical assessment are summarized in

Table 5. Technical adaptability scores of alternative fuels for MPHLVs using a multi-criterion scoring model.

Assessment Dimension	Conventional Fuel	LNG	Methanol	Ammonia	Hydrogen	Biofuel
Storage adaptability	15	2	15	5	2	15
Engine technology maturity	15	15	13	10	2	14
Cargo capacity utilization	15	10	13	12	8	14
Range capability	10	8	10	8	8	5
Cargo loading flexibility	15	2	15	12	2	15
Port compatibility	10	10	8	8	2	5
Supply chain stability	10	10	8	4	2	5
Safety and regulatory compliance	10	10	8	4	2	5
Total Score	100	67	90	63	28	78

.

As shown in Table 5, methanol demonstrates the highest technical adaptability among all alternative fuels (score: 90/100), followed closely by biofuels (78/100) and LNG (67/100). Methanol scores particularly well in storage adaptability, integration flexibility, and compatibility with cargo layout key considerations for MPHLVs. In contrast, ammonia and hydrogen, although promising in terms of long-term decarbonization potential, received significantly lower scores (63 and 28, respectively), primarily due to low technological maturity, poor cargo space efficiency, and underdeveloped bunkering infrastructure.

Figure 2 illustrates the comparative technical adaptability of six fuel types—Conventional Fuel, LNG, Methanol, Ammonia, Hydrogen, and Bio-fuel—across eight evaluation dimensions. The radar chart highlights methanol as the most technically compatible alternative for MPHLVs, achieving near-maximum scores in storage adaptability, cargo loading flexibility, and integration feasibility. Bio-fuels also perform well due to their compatibility with existing systems and low retrofit complexity. In contrast, hydrogen and ammonia score lower, reflecting current limitations in safety compliance, fuel infrastructure, and system maturity. These results confirm methanol’s technical feasibility as a mid-term decarbonization option for MPHLVs under current regulatory and operational constraints.

3.2. Results of Economic Analysis

The results of the technical adaptability analysis indicate that ammonia and hydrogen are currently not viable fuel options for MPHLVs due to significant limitations in safety, infrastructure, and technological maturity. As such, the economic evaluation in this study focuses solely on LNG and green methanol as the two most promising alternative fuels, benchmarked against low-sulfur fuel oil (LFO) as the conventional baseline, based on the average purchase prices and calorific values of these fuels in 2024 market. To support the economic modeling process, key fuel properties, including LCV, carbon conversion factor (CF), and GFI, are presented in

Table 6. Parameter values of conventional and alternative fuels used in economic analysis [30,36,37,38].

Fuel Type	LCV (kJ/kg)	CF (tCO2/tFuel)	GFI (gCO2eq/MJ)	Energy Equivalent Fuel Consumption (t)	EU Region Equivalent Fuel (t)	Average Price (USD/t)
LFO (baseline)	40,200	3.114	91.25	5958	1940	488
LNG	48,000	2.750	76.23	4990	1625	682
Green Methanol	19,900	1.375	32.9	12,036	3919	1113

. These parameters are used to calculate energy-equivalent consumption, CO₂-equivalent emissions, and total cost per ton of fuel under 2024 operational conditions.

As shown in Table 6, green methanol exhibits significantly lower GFI and CF compared to both LFO and LNG, reflecting its strong decarbonization potential. However, its lower energy density results in nearly double the required fuel mass to achieve equivalent propulsion output, which directly affects storage requirements and total operating costs.

In this analysis, LFO is used as the reference conventional fuel, while LNG is modeled based on high-pressure two-stroke dual-fuel engine systems currently in commercial use. For green methanol, a GFI value of 32.9 gCO₂eq/MJ is adopted, corresponding to the mainstream commercial standard available in the current market. Based on the average annual fuel consumption of 5958 tons per vessel observed in the analyzed fleet, the corresponding total energy consumption is calculated as 239.5 TJ. Similarly, the average fuel usage in EU/EEA amounts to 1940 tons, equivalent to 77.988 TJ of onboard energy demand in the regulated region. Using this energy-equivalent consumption as the comparative baseline, the quantities of LNG and green methanol required to deliver the same propulsion output were converted. These adjusted values were then applied to estimate total annual fuel costs, carbon allowances, and GHG compliance penalties under both EU and IMO regulatory frameworks.

The annual GHG intensity baselines defined by the EU FuelEU Maritime Regulation and the IMO Net-Zero Framework are summarized in

Table 7. Annual GHG intensity baseline targets under FuelEU Maritime and IMO Net-Zero Framework (unit: gCO₂eq/MJ).

Year	2025	2026	2027	2028	2029	2030	2031	2032	2033	2034	2035
FuelEU Target	89.34	89.34	89.34	89.34	89.34	85.69	85.69	85.69	85.69	85.69	77.94
IMO GFI BCT	-	-	-	89.57	87.70	85.84	81.73	77.63	73.52	69.42	65.31
IMO GFI DCT	-	-	-	77.44	75.57	73.71	69.60	65.50	61.39	57.29	53.18

. These values serve as key benchmarks in the calculation of compliance performance and penalty costs under each respective regime. While the FuelEU Maritime targets maintain a relatively steady trajectory until 2030, the IMO’s Base Compliance Target (BCT) and Direct Compliance Target (DCT) represent a more aggressive reduction pathway starting in 2028. According to the draft Net-Zero Framework, the GFI targets for the period 2036 to 2040 are scheduled to be determined by the Marine Environment Protection Committee (MEPC) no later than 1 January 2032. However, the framework explicitly mandates that the Z coefficient used to define the 2040 base compliance target must achieve a reduction of at least 65% relative to the 2008 baseline. These evolving targets form the basis for dynamic cost modeling in the economic analysis, particularly in assessing the long-term financial viability of different fuel options under increasingly stringent decarbonization policies.

Based on the fuel consumption equivalent and regulatory framework described in the previous sections, the total fuel costs of LFO, LNG, and green methanol from 2025 to 2035 were calculated and are summarized in

Table 8. Annual total fuel costs of different fuels under EU and IMO decarbonization policies (unit: USD).

Fuel Type	Cost	2025	2026	2027	2028	2029	2030	2031	2032	2033	2034	2035
LFO	Cfuel	2,907,504	2,907,504	2,907,504	2,907,504	2,907,504	2,907,504	2,907,504	2,907,504	2,907,504	2,907,504	2,907,504
	Ccarbon allowance	363,678	519,540	519,540	-	-	-	-	-	-	-	-
	CFuelEU Penalty	103,200	103,200	103,200	-	-	-	-	-	-	-	-
	CTier 1 RUs	-	-	-	289,795	289,795	289,795	289,795	289,795	289,795	289,795	289,795
	CTier 2 RUs	-	-	-	159,268	323,086	492,364	866,415	1,239,556	1,613,607	1,986,748	2,360,799
	Ctotal	3,374,382	3,530,244	3,530,244	3,356,567	3,520,385	3,689,663	4,063,714	4,436,855	4,810,906	5,184,047	5,558,098
LNG	Cfuel	3,403,180	3,403,180	3,403,180	3,403,180	3,403,180	3,403,180	3,403,180	3,403,180	3,403,180	3,403,180	3,403,180
	Ccarbon allowance	269,019	384,313	384,313	-	-	-	-	-	-	-	-
	CFuelEU Penalty	−708,351	−708,351	−708,351	-	-	-	-	-	-	-	-
	CTier1 RUs	-	-	-	0	15,089	60,594	158,789	256,984	289,795	289,795	289,795
	CTier2 RUs	-	-	-	0	0	0	0	0	246,637	619,778	993,829
	Ctotal	2,963,847	3,079,141	3,079,141	3,403,180	3,418,269	3,463,774	3,561,969	3,660,164	3,939,612	4,312,753	4,686,804
Green Methanol	Cfuel	13,396,068	13,396,068	13,396,068	13,396,068	13,396,068	13,396,068	13,396,068	13,396,068	13,396,068	13,396,068	13,396,068
	Ccarbon allowance	0	0	0	-	-	-	-	-	-	-	-
	CFuelEU Penalty	−3,049,531	−3,049,531	−3,049,531	-	-	-	-	-	-	-	-
	CTier1 RUs	-	-	-	−1,065,775	−1,022,665	−977,160	−878,965	−780,770	−682,575	−584,380	−486,185
	CTier2 RUs	-	-	-	0	0	0	0	0	0	0	0
	Ctotal	10,346,537	10,346,537	10,346,537	12,330,293	12,373,403	12,418,908	12,517,103	12,615,298	12,713,493	12,811,688	12,909,883

Notes: LNG and green methanol generate compliance surpluses under both FuelEU and the IMO Net-Zero Framework. These can be banked or used to offset deficits from other ships in the same fleet, resulting in negative penalty values (i.e., cost savings). “-” indicates an irrelevant item; “0” indicates a relevant item but the value is zero.

. The carbon allowances are calculated at EUR 80 per ton of CO₂, with a currency exchange rate of EUR 1 = USD 1.08. In addition to fuel purchase costs, the calculation incorporates penalties and credits under the FuelEU Maritime Regulation and the IMO Net-Zero Framework. Notably, negative values in the table represent credit offsets, where compliance surpluses (e.g., from LNG and green methanol) can be pooled within the fleet to compensate for traditional fuels’ non-compliance, thereby reducing the total cost of fuel usage across the fleet.

As shown in Table 8, LNG exhibits the most cost-effective profile between 2025 and 2030 due to moderate fuel prices and compliance credits. However, from 2031 onward, the tightening of IMO regulations increases its cost curve. Although green methanol incurs the highest absolute fuel purchase cost, its good emissions performance allows for significant cost offsets through regulatory credit trading, particularly after 2028. In contrast, LFO remains penalized throughout the forecast period, due to high carbon intensity and rising regulatory costs.

Figure 3 compares the projected total annual fuel costs for three different marine fuels—LFO, LNG, and Green Methanol—under EU and IMO regulatory frameworks.

(a) LFO exhibits an accelerating cost increase due to rising carbon allowances and compliance penalties after 2028.

(b) LNG maintains a relatively moderate cost trajectory, becoming more competitive than LFO from 2029 to 2032, though costs rise under IMO tightening.

(c) Green Methanol incurs the highest total cost, particularly after 2028, when the IMO Net-Zero Framework takes effect, despite benefiting from significant regulatory credits. Its high purchase price remains the dominant cost driver.

3.3. Limitations of This Study

3.3.1. Limitations in Technical Analysis

Among emerging zero-carbon marine fuel technologies, ammonia and hydrogen have attracted significant attention for their potential to eliminate GHG emissions. However, based on the multi-criterion technical adaptability assessment conducted in this study, both fuels show clear practical limitations under current conditions. These constraints are primarily observed across several critical dimensions:

(a) Technology maturity: Large-scale marine engines powered by ammonia or hydrogen are still in prototype development or limited testing phases. There are no commercially viable propulsion systems currently available that can meet the power requirements, system integration needs, and safety standards of large ocean-going MPHLVs.

(b) Fuel infrastructure readiness: The global bunkering network for ammonia and hydrogen remains underdeveloped. The lack of dedicated refueling facilities, especially in major international ports, poses a substantial barrier to route planning and operational continuity for MPHLVs.

(c) Operational and engineering challenges: Ammonia is toxic and corrosive, while hydrogen storage requires either extremely low temperatures or high-pressure systems, both of which introduce substantial engineering complexity and risk. These characteristics significantly increase system design and shipyard construction costs, while imposing stringent requirements on crew training and onboard safety management.

In the technical evaluation model developed in this study, ammonia and hydrogen consistently received low scores in multiple dimensions, including system compatibility, storage adaptability, and port accessibility. Even under hypothetical scenarios where fuel prices decline or carbon regulations tighten, these two fuels remain technically unviable for MPHLV applications in the near term. As a result, although ammonia and hydrogen may hold long-term potential, methanol, with its moderate emissions profile, established industrial base, and relatively simple handling requirements emerges as a more technically and economically feasible transitional fuel solution for the current phase of maritime decarbonization.

3.3.2. Limitations in Economic Analysis

To assess the robustness of the techno-economic feasibility of methanol-fueled MPHLVs, an uncertainty analysis was performed on key factors that significantly influence total fuel cost outcomes. This analysis considered four primary fuel types: LFO, LNG, and green methanol.

(a) Fuel price volatility: The unit cost of marine fuels is subject to sharp fluctuations driven by geopolitical instability, supply demand dynamics, and evolving production technologies. Historical trends indicate that LFO maintains the lowest price, followed by LNG and methanol. Green methanol, while currently the most expensive, is expected to decrease in cost as renewable production scales up and supply chains mature.

(b) Carbon pricing and regional compliance mechanisms: The expansion of the EU ETS into the maritime sector has significantly altered the competitive cost landscape for marine fuels. Concurrently, the FuelEU Maritime Regulation imposes escalating penalties for exceeding GHG intensity thresholds, with compliance costs directly linked to lifecycle carbon emissions. Under this policy framework, fuels like LFO incur disproportionately higher emission-related expenses, while green methanol and LNG benefit from regulatory credits or reduced penalties due to their lower GHG intensity.

(c) Global regulatory developments: The forthcoming IMO Net-Zero Framework, scheduled for implementation in 2028, will introduce additional compliance burdens. The dual-track system of GHG intensity targets and economic penalties under the IMO framework will amplify the cost disparities between high-carbon and low-carbon fuels. As carbon pricing increases and regulatory thresholds tighten, economic sensitivity to fuel choice will intensify.

In summary, this sensitivity analysis highlights the importance of incorporating dynamic regulatory and market variables into the economic evaluation of alternative fuels. While methanol may not currently exhibit the lowest total fuel cost, its relative insulation from future carbon penalties and growing industrial viability make it a strong candidate for near-to-medium-term deployment in the MPHLVs. However, as discussed and concluded in reference [24], the selection of alternative fuels faces various uncertainties, including ship type, ship size, fleet size, carbon trading price, the availability of fuels, ship purchase cost and retrofitting cost, shipping demand and charter rates, the interest rate, etc. Therefore, more sophisticated and robust models than the one established in this article are expected to be developed to achieve a reliable transition to a net-zero emission shipping.

4. Case Study of a Methanol-Fueled MPHLV

4.1. Traditional Fuel Power System

To explore the feasibility of methanol propulsion in MPHLVs, this study selects a 38,000 DWT MPHLV with a latest-generation hull design and conventional fuel-based power system as the reference case. The vessel features a forward-positioned bridge, a large-capacity open cargo hold, and an uninterrupted flat deck loading area, representing a state-of-the-art layout optimized for deck cargo transportation. However, the current power system is configured for traditional fossil fuels. The power system configuration is summarized in

Table 9. Power system configuration of 38,000 DWT MPHLV with traditional fuels.

ME	WinGD 6X52-S2.0-HPSCR Tier III
SMCR	6940 kW@92 r/min
CSR (85% SMCR)	5899 kW@87.1 r/min
Main generator	1000 kWe × 3
Endurance	15,000 nm
LFO	1500 m3
VLSFO	500 m3
MGO	250 m3

. The vessel is equipped with three distinct types of fuel tanks to meet various operational requirements under different environmental zones:

(a) 1500 m³ LFO tanks, for long-range transoceanic operations in non-ECA (Emission Control Area) zones, located within the transverse bulkhead between the forward and aft cargo holds.

(b) 500 m³ VLSFO tank, for compliance in ECA-regulated sea areas, located in the bulkhead between the engine room and the cargo hold.

(c) 250 m³ MGO tank (Marine Gas Oil), for low-emission operations during port stays, located in and near the engine room.

This arrangement efficiently utilizes internal structural compartments without encroaching on cargo space, representing a mature and rational tank layout solution for conventional fuel applications.

4.2. Methanol-Fueled Main and Auxiliary Power Unit

To support the transition from conventional fuels to methanol, this study investigates the selection of main and auxiliary power units for the methanol-fueled variant of the 38,000 DWT MPHLV. The focus is on the application of methanol dual-fuel low-speed marine internal combustion engines, which can operate on both methanol and marine diesel oil (MDO) for ignition support and backup.

Currently, several leading manufacturers—MAN Energy Solutions (MAN, renamed Everllence from June 2025, Augsburg, Germany), WinGD (Winterthur, Switzerland), and China State Shipbuilding Corporation Power Group (CSSC Power, Shanghai, China)—offer mature methanol capable engine models tailored for different vessel scales and propulsion requirements. These engines typically use methanol as the primary fuel and diesel as pilot fuel, featuring seamless switching, high thermal efficiency, and compliance with IMO Tier III NO_x limits when used with SCR or EGR systems. The available methanol dual-fuel engine models with varying power ratings are summarized in

Table 10. Methanol dual-fuel low-speed engine model.

Brand	Model	Application Project
MAN	G95ME-C10.5-LGIM	Maersk 16,000 TEU
	G80ME-C10.5-LGIM	/
	G60ME-C10.5-LGIM	/
	S60 ME-C10.5-LGIM	/
	G50ME-C9.6-LGIM	50,000-ton chemical tanker Guangzhou Shipyard International
	S50ME-C9.6-LGIM	New Dayang 1170 TEU
	S50ME-C10.7-LGIM
	G45 ME-C9.7-LGIM	/
WinGD	X92DF-M-1.0	COSCO SHIPPING 16,000 TEU
	X82DF-M-1.0	/
	X72DF-M-1.0	/
	X62DF-M-1.0	/
	X62DF-M-S1.0	/
	X52DF-M-S1.0	/
	X52DF-M-1.0	/
CSSC Power	CX40DF-M	Testing

.

The final engine selection for this study will be based on the operational profile, design speed, and hull resistance characteristics of the 38,000 DWT vessel, taking into account fuel efficiency, the available methanol supply chain, and integration feasibility with the existing engine room layout. Currently, the only engine with similar power available is MAN’s 6S50ME-C10.7-LGIM-HPSCR, and the fuel consumption rate parameters compared with the original model are shown in

Table 11. Main engine selection table.

Model	SMCR (kW)	Speed (r/min)	CSR (kW)	Speed (r/min)	Tier II Fuel Consumption SMCR, ISO (g/kWh)	Tier II Fuel Consumption CSR, ISO (g/kWh)	Tier II Methanol Consumption Rate SMCR, ISO (g/kWh)	Tier II Methanol Consumption Rate CSR, ISO (g/kWh)
WinGD 6 X52-S2.0-HPSCR Tier III	6940	92	5899	87.1	~161.1	~153.8	—	—
MAN 6S50ME-C 10.7-LGIM-HPSCR Tier III	6940	92	5899	87.1	~165.1	~161.3	~324.2	~312.1

.

In addition to the main propulsion engine, the selection and adaptation of auxiliary power generation units is essential to ensure operational reliability under variable load conditions, particularly during low-load voyages, port stays, and maneuvering in emission-controlled areas. For methanol-powered MPHLVs, the auxiliary generator system must either be dual-fuel capable, allowing switching between methanol and MDO, or operate as a methanol-only system, equipped with a methanol-compatible combustion system and integrated safety features. Several manufacturers now offer methanol dual-fuel medium-speed internal combustion engines, designed for auxiliary power generation. These engines generally operate on methanol with diesel pilot injection and feature automatic switching modules to adapt to variable power demands. This not only ensures fuel flexibility but also supports the ship’s compliance with emissions regulations in both ECA zones and IMO decarbonization pathways. The available methanol-compatible medium-speed engine models suitable for generator applications are summarized in

Table 12. Methanol dual-fuel medium-speed engine models.

Brand	Model	Single Cylinder Power kW/Cylinder	Application Project
MAN (Augsburg, Germany)	L21/31DF-M	220	/
Wärtsilä (Helsinki, Finland)	L32M	580	/
Hyundai (Ulsan, Republic of Korea)	H32DF-LM	500	Maersk 16,000 TEU
CSSC 711 (Shanghai, China)	CS21M3	200	/
CSSC Power (Shanghai, China)	M320DF-M	405	Under development
Zibo Diesel Engine Factory (Zibo, China)	Z170	75	/

.

The final selection of auxiliary generator sets for the 38,000 DWT methanol-fueled MPHLV must comprehensively address the vessel’s operational profile, safety standards, and energy efficiency targets. Specifically, the decision-making process considers the following technical and functional criteria:

(a) Power demand matching: The selected generator set must align with the vessel’s hotel load and auxiliary equipment requirements across various operational modes (cruising, berthing, cargo operations).

(b) Integration with existing systems: Spatial compatibility with the engine room layout and interoperability with control, monitoring, and fuel supply systems is essential for seamless integration.

(c) Safety and ventilation design: Methanol’s low flashpoint and vapor dispersion characteristics require robust ventilation systems and fire suppression measures in enclosed compartments.

(d) Shore power and hybrid compatibility: Auxiliary systems should ideally support shore connection and allow operation under hybrid configurations where required by future port emission standards.

When combined with a methanol dual-fuel main propulsion engine, the tailored auxiliary generator setup provides a holistic low-emission power solution, ensuring the vessel’s compliance with both regional and global decarbonization strategies. Among commercially available and developmental methanol-fueled medium-speed engines, the Wärtsilä L32M is a high-output unit delivering 580 kW per cylinder. While this engine is technically advanced and efficient, its power density exceeds the typical requirements for general cargo and auxiliary applications in MPHLVs, making it more suitable for larger, power-intensive ship types. In contrast, medium-speed methanol engines currently under development or test by MAN Energy Solutions and CSSC 711 Research Institute offer configurations more suited to auxiliary power generation. Their designs favor modularity, better methanol substitution ratios, and adaptability to compact onboard environments. A comparative overview of known engine models and their fuel consumption characteristics is summarized in

Table 13. Main generator selection.

Model	MCR (kW)	Speed (r/min)	Fuel Consumption MCR, ISO (g/kWh)	Methanol Consumption Rate MCR, ISO (g/kWh)	Methanol Substitution Rate (%)
5L21/31DF-M	1100	1000	~192	~380.0	~60
6CS21M3	1200	1000	~197	~390.0	>90

. Preliminary analysis reveals that while the 5L21/31 DF-M engine exhibits a lower methanol substitution rate, the CSSC 6CS21M3 model demonstrates a higher efficiency in methanol-only operation, making it more favorable for use as an auxiliary power unit on this vessel type.

4.3. Methanol Fuel Tank Design

Based on the endurance and operational profile of a 38,000 DWT MPHLV, the total methanol fuel tank capacity is designed to be 3000 m³ to meet the ship’s voyage autonomy and energy consumption requirements. The tank layout scheme incorporates both retrofitting and structural optimization principles, as follows:

(a) The existing 1500 m³ fuel tank located between the forward and aft cargo holds is modified into a dual-purpose fuel/methanol tank, leveraging its central position and structural integrity. The inner surface is coated with MARINELINE 784 by Advanced Polymer Coatings (APC, Avon, OH, USA), a commercially available and proven cargo tank coating solution compatible with both methanol and marine fuels.

(b) An additional 1500 m³ dedicated methanol tank is installed forward of the cargo holds, in the lower section of the bow beneath the accommodation block. The tank’s protective coating uses inorganic zinc-rich silicate paint, suitable for methanol compatibility and long-term corrosion resistance.

As shown in Figure 4, the modified tank arrangement minimally alters the original vessel layout, ensuring negligible cargo hold volume loss and structural efficiency.

The new tank system is configured as a fully enclosed and independent structural unit, surrounded by void spaces for containment and thermal isolation. A-60 fireproof partitions are applied between the methanol tank and adjacent structures to enhance passive fire protection. To ensure safety and environmental compliance, the ventilation system for both methanol tanks is designed as a closed-loop system. Vent lines from both tanks are connected and routed to a gas–liquid separation cabinet installed in the engine room. The cabinet’s gas outlet is further directed to the chimney-side oil mist exhaust box, thereby reducing the risk of vapor accumulation and enabling integrated fire suppression and pressure control.

4.4. Methanol Auxiliary System Configuration

The integration of methanol fuel into shipboard operations requires a comprehensive auxiliary system tailored to the unique physical and chemical characteristics of methanol. For the hybrid configuration of dual-purpose and dedicated methanol tanks, all supporting systems must be engineered in strict accordance with the IGF Code and classification society guidelines. The specific system design requirements are summarized in

Table 14. Methanol auxiliary system configuration requirements.

Name	System Components	Fuel Tank	Methanol Dedicated Tank	Fuel Oil/Methanol Combined Tank
Injection System	Filling station ESD system		×	×
	Fuel filling pipe	×		×
	Methanol injection pipe		×	×
	High level and high-high-level sensors	×	×	×
	Temperature Sensor	×	×	×
	Pressure Sensors		×	×
Breathable System	Open air pipe head	×
	Controlled breather valve		×	×
	Boil-off gas recovery line		×	×
	Cabin pressure sensor		×	×
Supply System	Fuel supply system	×		×
	Methanol supply system		×	×
	In-cabin methanol transfer pump		×	×
	Double wall pipe		×	×
	Oil supply unit steam heating system	×		×
	Methanol unit ethylene glycol heat exchange system		×	×
Fire Protection System	Fixed alcohol-resistant foam fire extinguishing system for filling stations		×	×
	Fixed alcohol-resistant foam fire-extinguishing system for Class A machinery spaces/fuel preparation rooms		×	×
	Methanol tank fixed alcohol-resistant foam fire extinguishing system (when located on open deck)		N/A	N/A
	Fire water	×	×	×
	Water spray system (when methanol tank is located on open deck)		N/A	N/A
	Portable fire extinguisher		×	×
Nitrogen System	Nitrogen generator		×	×
	Nitrogen tank		×	×
	Oxygen detection sensor		×	×
	Nitrogen injection tube		×	×
	Isolate empty space with nitrogen protection or ventilation, or water injection measures		×	×
Bilge System	Tank discharge		×	×
	Isolate the independent bilge water in the empty tank		×	×
Gas Detection Systems	Isolation cabin		×	×
Ventilation System	Double wall pipe mechanical exhaust		×	×
Fire Protection Arrangement	A60 fireproof insulation		×	×
	Isolation cabin	×	×	×

Note: × means Applicable.

, which outlines the functional objectives, safety standards, and design compliance references for each subsystem. This methanol fuel support system architecture ensures operational safety, system integrity, and regulatory compliance, while maintaining the flexibility required for MPHLVs operating across diverse cargo profiles and international routes.

5. Conclusions

5.1. Summary of Main Findings

This study employed a comprehensive evaluation method to evaluate the technical adaptability of alternative marine fuels for MPHLVs. Based on eight dimensions, six types of marine fuel were scored and compared systematically. The results demonstrate that the proposed evaluation system offers a scientifically grounded and quantifiable approach to assessing fuel compatibility across ship types. The evaluation results indicate that methanol fuel achieved the highest score of 90, significantly outperforming LNG’s score of 67. Although biofuels scored 78, their limited production capacity prevents them from being a viable long-term solution. Consequently, methanol fuel exhibited the highest technical adaptability to MPHLVs under current technological and regulatory conditions.

On the economic front, a total fuel cost assessment model was developed using real-world operational data from 12 MPHLVs in 2024. The model incorporates both fuel procurement costs and carbon emission-related expenses, enabling a full life-cycle cost comparison among LFO, LNG, and green methanol. The findings indicate that LNG currently offers the best cost efficiency; despite its environmental advantages, the total cost of green methanol remains approximately three times that of LNG fuel, which is hindered by high production and supply chain costs.

Furthermore, based on a newly designed 38,000 DWT MPHLV, the study proposes an integrated methanol propulsion system solution. This design fills a critical gap in the application of methanol in the heavy-lift shipping segment and provides valuable technical references for future ship design and retrofitting toward low-carbon goals.

5.2. Application Prospects of Methanol Fuel in MPHLVs

Methanol, as a liquid fuel with relatively low storage complexity and mature handling infrastructure, shows promising technical feasibility for application in MPHLVs characterized by complex structures and high demands for cargo space utilization. While green methanol currently lacks competitiveness in cost, especially due to immature global supply chains, its decarbonization potential and regulatory compliance value under future climate policies position it as a strong candidate for medium- and long-term adoption.

In the near term, operators can pursue a hybrid compliance strategy, combining traditional fuels and biofuels with carbon offset mechanisms. In the longer term, as green methanol production scales and unit costs decline, it will become a viable route to meet the IMO 2050 zero-carbon target. Compared with zero-carbon fuels such as ammonia and hydrogen, which still face challenges in safety, storage, and system maturity, methanol offers a more practical transition pathway with better engineering readiness and near-term deployability for MPHLVs.

5.3. Research Limitations and Future Research Directions

Given the analysis of research limitations presented in Section 3.3, this study is grounded in the current state of fuel technologies and infrastructure. While ammonia and hydrogen fuels were evaluated in terms of their technical readiness, their inclusion was limited to qualitative assessments due to the lack of large-scale deployment and real-world validation data. Moreover, the economic analysis is based on 2024 average prices and carbon allowance policies, which are subject to market volatility and policy evolution. The long-term economic viability of alternative fuels will depend on variables such as fuel price dynamics, carbon pricing schemes, and regulatory compliance thresholds. This is the drawback of this research.

Given the ongoing R&D in these areas, the conclusions on their adaptability are inherently time-sensitive and should be revisited as advancements occur in power systems, storage safety, and bunkering infrastructure. Future studies should incorporate scenario-based modeling, accounting for diverse policy trajectories, cost-learning curves, and supply–demand shifts, to enhance the robustness and foresight of economic projections.