Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

I have reviewed the new version of your manuscript. You have made most of the corrections that I indicated. Your work has become more structured and clear. In this form it can be recommended for publication.

Author Response

Dear Reviwer, 

We wholeheartedly appreciate your time and feedback. 

Thank you again.

Sincerely,

Dr Hamed Majidiyan

Reviewer 2 Report

Comments and Suggestions for Authors

Based on operational data from a hydrogen fuel cell demonstration vessel, this study developed a regulatory-compliant competency and training framework for marine engineers, proposing six core competency domains and a 40-hour training module. Its strengths lie in its practical approach, filling a key gap from technical expertise to assessable training, and its systematic framework, including an implementation roadmap. However, its limitations include the limited evidence from small demonstration vessels, and the framework's applicability to large commercial vessels and its integration with existing certification systems require further evaluation.

The content of the manuscript is within the scope of the journal and can be of broad interest to readers. However, in terms of specific content, there is still room for improvement. Therefore, I decided to make the decision of major revision. It is recommended that the author properly absorb the reviewers' comments and make corresponding improvements and enhancements.

1. For the keywords, 'Demonstration Ship Anchoring', 'Regulatory Framework', 'IGF/LNG Incremental Training', and 'Digital Twin/VR Training' should be added to attract a broader readership.  

2. The authors explicitly state that this paper fills the gap between "system development" and "evaluable training" and proposes a framework encompassing six capability domains. This is a valuable contribution. However, the manuscript's explanation of the core methodological contribution of "demonstration vessel anchoring" is somewhat weak. In the current manuscript, the demonstration vessel's data (such as pressure, current, and SOC response) are primarily described as "operational anchor points" rather than calibrated performance verification evidence. This weakens its weight as scientific "evidence."
    It is recommended that the "Introduction" or "Research Methodology" section provide a more in-depth argument regarding why and how to transform the operational data of a small experimental vessel into a general capability framework applicable to a wider range of more complex commercial vessels. This involves a philosophical and methodological discussion of the "scale transfer" problem, which should be more systematically elaborated to strengthen the rationality of the research design.
    
3. The manuscript, in describing the operational data of the demonstration vessel, mentions monitoring 'PEMFC charging behaviour' and temperature. Tang et al.'s research deeply reveals the temperature sensitivity of the PEM fuel cell state of health (SOH) and its impact on durability, providing crucial mechanistic support for the capability domain of "fuel cell system monitoring" [Chemical Engineering Journal 491 (2024): 151951].  It helps authors elevate the simple task of "temperature monitoring" to a theoretical understanding of how temperature fluctuations accelerate ageing and affect long-term safe operation, thereby enhancing the scientific rigour and forward-looking nature of the "preventive maintenance" and "system health assessment" sections in the training framework. It is recommended to discuss this when discussing PEMFC operational monitoring or system durability.

4. The manuscript points out that hydrogen fuel cell systems exhibit the "largest capability increment" in a specific area compared to IGF/LNG training, which is an important finding. However, the current description is qualitative.
     A more systematic comparative analysis is recommended. A simple analytical framework could be designed to compare the capability units in the IGF Code or LNG training model courses with the six capability domains proposed in this paper, clearly marking in tabular form which capabilities are "completely transferred," "partially modified," or "completely added." This would concretise the "increment" and highlight the unique training needs of hydrogen fuel cell systems.

5. Including digital twins/VR as part of an implementation roadmap is forward-thinking, but current discussions remain at the level of "supporting visualisation and repeatability," failing to delve into how it specifically addresses the core training challenges identified in this paper, such as scale transfer and high-risk scenario drills. Therefore, the "Discussion" section should be expanded to include relevant content. Specifically, it should explain which competency domains are best suited for training in a digital twin/VR environment and how it compensates for the limitations of small demonstration vessels in simulating the consequences of large-scale system failures. More literature on the effectiveness of immersive simulation in high-pressure skills training and team collaboration could be appropriately cited to support the arguments.

6. The manuscript emphasises the importance of integrated monitoring and communication under "abnormal operation" conditions. Li et al. proposed a self-optimising control strategy for the oxygen excess ratio under dynamic conditions, which is the core control issue ensuring the efficient and safe operation of PEMFCs under dynamic conditions such as load changes [Processes 12.12 (2024): 2807]. This content can greatly strengthen the manuscript's discussion on handling "dynamic conditions" and "abnormal responses." It will help authors expand the training framework from basic "monitoring and isolation" operations to a higher level of capability requiring an understanding of advanced adaptive control logic, making the framework more comprehensive and better able to handle complex dynamic scenarios in actual operation. It is recommended to refer to this when discussing dynamic operation, abnormal condition handling, or control logic training.

7. The manuscript mentions the limitations of the demonstration vessel's size and scale transfer issues, but as a study aiming to provide a general framework for the industry, the discussion of its limitations should be more comprehensive and in-depth. It is recommended to include a separate "Limitations and Future Work" section in the "Discussion" or "Conclusion" paragraphs. In addition to size, the following should also be discussed: the framework's universality, such as its applicability to liquid hydrogen or ammonia-hydrogen mixed systems; the potential differences in specific capability requirements for different vessel types; and the institutional challenges that the framework may face when integrated into existing seafarer certification systems (such as STCW).

8. The abstract effectively summarises the research question, methodology, and key findings. However, the concluding sentence, "The framework is proposed as a pilot pathway... not as evidence of commercial-vessel readiness or for full certification," is somewhat defensive and may weaken its impact.
    It is recommended to rewrite this sentence, emphasising the framework's value in a more positive and forward-looking tone. For example: "The framework proposed in this study provides a pilot pathway and structured approach for translating operational testing evidence into assessable maritime education and training, laying an important foundation for the future development of comprehensive commercial vessel crew certification standards."

9. The manuscript explicitly mentions that "voltage sag" is one of the key data points monitored on the demonstration vessel, which is directly related to the voltage stability issues of multi-reactor PEMFC systems during testing or dynamic operation. Zhao et al. (10.3389/fenrg.2026.1731457) focus on improving bus voltage stability through enhanced extended state observer design, and their contents can provide a solid engineering methodology reference for the "battery buffer propulsion monitoring" and "voltage stability management" sections of the manuscript. It connects the observation point of "voltage sag" to more advanced control theories and solutions, thereby strengthening engineers' understanding and response capabilities to system voltage dynamics within the training framework and enhancing the framework's technical depth. It is recommended to involve this when analysing voltage-related anomalies or discussing control system training.

10. The English writing is generally fluent, but some sentences are long and structurally complex, which may affect readability. Some technical terms are not explained upon their first appearance (e.g., "LFP," although it can be inferred to be lithium iron phosphate, it is recommended to spell it out throughout the entire text).
     Recommendations: ① Break down excessively long sentences to ensure clear subject-verb-object relationships; ② In the "Introduction" or "System Description" sections, spell key abbreviations such as "PEMFC-LFP" completely; ③ It is recommended to conduct a thorough polishing of the language, checking prepositional phrases, article usage, and tense consistency to ensure compliance with SCI journal publication standards.

Author Response

Dear Reviwer, 

We wholeheartedly appreciate your time and feedback. Please kindly find the point-to-point response in the attached PDF file under reviewer #2.

Thank you again.

Sincerely,

Dr Hamed Majidiyan

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript develops a demonstrator-informed competency and training framework for marine engineers operating compressed-hydrogen PEMFC–battery hybrid propulsion systems, combining operational observations from a small test vessel with regulatory and training literature. It proposes six competency domains, learning outcomes, assessment approaches, a 40-hour training module, and an implementation roadmap intended as a pilot educational framework rather than validation of commercial hydrogen vessel operations.

The manuscript is relevant and timely, but it is primarily an educational framework paper, not an engineering paper.

Introduction

• The existing competency-framework literature review is limited. No systematic comparison with existing hydrogen training programs.
• Please, try to answer the following questions: What frameworks currently exist worldwide? Why is IGF training insufficient?

Materials and methods

• The narrative synthesis lacks reproducibility and the search strategy is insufficiently rigorous.
  The article does not present a PRISMA-type methodology.
• Were experts consulted about the search?
• This section should include: A PRISMA flow diagram, inter-reviewer reliability and a Delphi validation.

Results

• The results are largely conceptual as the demonstrator data are extremely limited.
• There is no uncertainty analysis.
• Why are only illustrative operational values presented? How representative are the measurements? Were tests repeated?

Discussion

• The discussion mostly restates results, there's limited critical reflection.
• The comparison with previous literature is scarce. 
• There are come questions that this section could answer: How would framework scale to commercial vessels? How would it apply to liquid hydrogen? How would certification authorities adopt it? What costs are involved? How would training effectiveness be assessed?
• Please, discuss economic feasibility and include educational evaluation metrics.

Conclusions

• The conclusions are stronger than evidence supports. The framework validation is absent and the educational effectiveness untested.

Also, for the figures:

Fig1: Replace with a methodology workflow and evidence coding map.

Figs 3 and 4: Provide engineering schematics.

Fig 5: There's no uncertainty, no repetitions and no statistical interpretation.

Overall, the paper presents a potentially useful pilot framework but requires significant strengthening of validation, methodology, and scientific depth before publication in a high-impact journal.

Comments on the Quality of English Language

The English is understandable but requires substantial editing to avoid redundancies and double conjunctions.

Author Response

Dear Reviwer, 

We wholeheartedly appreciate your time and feedback. Please kindly find the point-to-point response in the attached PDF file under reviewer #3.

Thank you again.

Sincerely,

Dr Hamed Majidiyan

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

The reviewer suggests that the authors include some quantitative results in the abstract section.

 

The reviewer suggests that the authors also discuss, in the literature review, about the different hydrogen production system, posing, in particular, the attention on the green ones.

 

What is the hydrogen pressure in the supply?

 

The reviewer suggests that the authors further extend the methodology section. They well describe the structure, but more information is required about system pressure, temperature, mass or volume flow and so on.

 

What is the size of the stack considered?

 

“The records should be interpreted as indicative training values rather than calibrated performance-validation data because full instrument calibration, uncertainty bands, environmental corrections and repeatability trials were not available”. The reviewer does not completely agree with this sentence. In particular I suggest that the authors provide information on the measurement and control instruments including also their accuracies. As example, data from the datasheet can be useful.

 

The reviewer suggests that the authors in figure 2 clearly indicate the y-axis for each curve.

 

The reviewer suggests that the authors include in table also the strategies required to avoid hazards.

 

The reviewer suggests that the authors provide a weighting coefficient for each risk to characterise the different time presented in figure 7.

 

In the reviewer opinion, it is not completely clear if the authors already realized a digital twin of the pilot model or not.

Author Response

Dear Reviwer, 

We wholeheartedly appreciate your time and feedback. Please kindly find the point-to-point response in the attached PDF file under reviewer #4.

Thank you again.

Sincerely,

Dr Hamed Majidiyan

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

As a reviewer, I appreciate the authors' detailed and conscientious revisions in response to the first round of comments. The revised manuscript shows significant improvement in its focus, logical coherence, and articulation of contributions—particularly regarding the clarification of competency gaps, the refinement of training module designs, and the discussion of limitations and future work. The manuscript is now very close to meeting the journal's publication standards. However, during the second review, I identified a few areas that require further clarification. Therefore, I recommend acceptance subject to these minor revisions. Specific comments are as follows:

1. The manuscript astutely identifies the issue of "scale transition" between demonstration vessels and commercial ships, citing "digital twin/VR" technologies as a complementary solution. However, this raises a deeper question regarding training design: within the proposed "40-hour training module," how should instructional hours and content priorities be specifically allocated among "hands-on operation of physical demonstration vessels," "digital simulation training," and "vessel-specific familiarisation"? Is there a guiding principle or matrix to help designers determine which competencies require physical equipment, which can be achieved through simulation, and which must be addressed only after crew members board the actual vessel? Elaborating on this aspect would enhance the implementation roadmap's practicality.

2. A highlight of the manuscript is the description of the research methodology as a "structured purposive narrative synthesis." However, the description of how this method is applied in the specific context—namely, the systematic integration of heterogeneous evidence such as project deliverables, regulatory and safety documents, existing maritime training logic, competency framework literature, and operational records from the demonstrator vessel—remains somewhat brief. Please elaborate on the key steps of the synthesis process (such as the assignment of evidence weight and principles for handling conflicting evidence) and explain how the method ensures the "defensibility" of the final framework, rather than it being merely an induction based on the demonstrator vessel's experience. Addressing this will help anticipate and counter potential methodological challenges.

3. Pages 2–3 of the manuscript emphasise the need for engineers to monitor fuel cell status but do not delve deeply into the impact of operational behaviours on cell lifespan. For instance, "reversible voltage loss" and the associated recovery phenomena—occurring during start-stop cycles and load fluctuations—directly influence long-term system performance assessment and maintenance strategies. When discussing "specific fuel cell purging and shutdown logic" or the ability to "interpret system status," the authors may refer to Journal of Power Sources 625 (2025): 235634. The related quantitative study on voltage recovery mechanisms in fuel cell lifespan prediction provides a solid scientific basis for explaining why engineers should understand specific operating procedures; linking operational protocols to underlying electrochemical principles would add scientific depth to the training framework.

4. A core contribution of the manuscript is the derivation of six key competency areas based on a demonstration vessel project. However, beyond the comparison with the IGF/LNG framework, has this framework undergone broader validation? For instance, have additional experts on hydrogen fuel cell vessels—from classification societies, shipping companies, or established training institutions—been consulted to confirm the completeness and relevance of these competency areas? It is recommended to add a brief paragraph in the discussion section acknowledging that, while the framework is grounded in a demonstration vessel and existing literature, its general applicability requires further validation through methods such as the expert Delphi technique or pilot training programs on larger vessels; this would lend greater foresight and rigour to the manuscript's conclusions.

5. Regarding the digital twin/VR supplementary training proposed on pages 3 and 5: while this is a valuable suggestion, the current description is somewhat general. Please elaborate on the key scenarios that the envisioned digital twin/VR environment needs to simulate—such as specific fault injection, load management under varying sea states, and multi-person collaborative emergency response—and explain how these scenarios directly link to the "assessable learning outcomes" proposed in the manuscript. Additionally, it is recommended to briefly discuss the current maturity of such technologies in the maritime training sector, cost considerations, or known successful case studies.

6. Page 3 of the manuscript mentions the need for temperature monitoring but treats thermal management merely as a standard parameter. For liquid-cooled PEMFC systems, however, thermal management is central to safety and efficiency, encompassing issues such as cooling system failure, the risk of localised overheating, and system efficiency optimisation. It is recommended to refer to 10.1016/j.jpowsour.2025.237227 within the "Integrated Safety Monitoring" or "Response to Abnormal Operation" sections. This review article systematically summarises the latest advancements, challenges, and solutions regarding thermal management in liquid-cooled PEMFCs, thereby providing essential technical context for the manuscript's emphasis on the need for engineers to understand coupled system interactions. Incorporating this material would significantly enhance the technical currency of the training content and demonstrate that the framework design addresses key challenges in current engineering practice.

7. The manuscript repeatedly emphasises "assessable learning outcomes" and "observable behaviours," which lie at the core of competency-based training. However, the assessment criteria for these outcomes (e.g., "performing satisfactorily" or "correctly identifying") remain somewhat subjective in their current descriptions. Are there plans or recommendations to develop more granular assessment rubrics—incorporating behaviorally anchored rating scales—for these key outcomes? Even if this cannot be fully realised within the scope of the current study, it is important to highlight this as a crucial step toward future standardisation and ensuring inter-rater consistency.

 

Author Response

Dear Reviewer,

We sincerely appreciate the time you have devoted to reviewing our manuscript and your constructive comments. We have carefully addressed each of your concerns and hope that the revisions satisfactorily respond to the points raised.

Best regards,

Hamed Majidiyan

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The article can be accepted for publication.

Author Response

Dear Reviewer,

We sincerely appreciate the time you have devoted to reviewing our manuscript and your constructive comments. 

Best regards,

Hamed Majidiyan

Reviewer 4 Report

Comments and Suggestions for Authors

The authors have addressed all my comments. Therefore, the paper can be accepted

Author Response

Dear Reviewer,

We sincerely appreciate the time you have devoted to reviewing our manuscript and your constructive comments. 

Best regards,

Hamed Majidiyan