Comparative Analysis of Carbon Intensity Indicators Applicable to Harbor Tugboats

1. Summary

Thank you very much for taking the time and effort to thoroughly review this manuscript. We sincerely appreciate your valuable feedback, which has allowed us to improve the clarity and quality of our work. Below, you will find detailed responses to each of your comments, along with the corresponding corrections highlighted in yellow in the re-submitted files. We hope these revisions meet your expectations and further enhance the contribution of this research..

2. Questions for General Evaluation

Reviewer’s Evaluation

Response and Revisions

Is the content succinctly described and contextualized with respect to previous and present theoretical background and empirical research (if applicable) on the topic?

Yes

Are the research design, questions, hypotheses and methods clearly stated?

Can be improved

Thank you for noticing. We hope the corrections made have improved the research design.

Are the arguments and discussion of findings coherent, balanced and compelling?

Can be improved

Thank you, We have enhanced the coherence in the results and discussion section.

For empirical research, are the results clearly presented?

Yes

Is the article adequately referenced?

Can be improved

Thank you for your comment. We have added some references to improve this point.

Are the conclusions thoroughly supported by the results presented in the article or referenced in secondary literature?

Yes

3. Point-by-point response to Comments and Suggestions for Authors

Comments 1: Data scope: the study is based on data from a single fleet. Expanding the analysis to include other fleets would enhance the generalizability and robustness of the findings.

Response 1: Thank you for pointing this out. We agree with this comment. Nevertheless, since access to real data from other companies is not available, we are unable to include data from other fleets. This information is confidential.

Comments 2: Consideration of additional operational factors incorporating variables like vessel age, maintenance schedules, and environmental factors (e.g., weather conditions) would provide a more comprehensive understanding of carbon intensity and its fluctuations.

Response 2: We agree with your comment, and we will consider it in a second phase, where we will conduct onboard measurements to refine the estimation and carry out the corresponding sensitivity analyses.

Comments 3: Potential overfitting: as the study uses data from one fleet, testing the model's applicability with external datasets or using cross-validation would increase the reliability and broader applicability of the results.

Response 3: Thank you for bringing this up, we highly value this type of feedback. As mentioned earlier, due to the confidentiality of the information, we cannot include those data. However, given that the global fleet of tugboats is somewhat homogeneous, the model would apply to other tugboat fleets. It would be very interesting, though, to empirically validate its applicability to other fleets.

Comments 4: Interpretation of variability in indicators: the study should explore the implications of the lower variability in energy consumption. Does it suggest operational consistency, or could it reflect inefficiencies that more dynamic indicators might reveal?

Response 4: Thank you for your insightful observation. We have thoroughly discussed and analyzed it, and we can conclude that this lower variability in the indicators suggests operational consistency within the fleet, based on our observations. Additionally, for central measures, it provides representativeness, which would not be achievable with large variations. However, as seen in the coefficient of variation, the selected indicator is not completely homogeneous, meaning that these fluctuations allow for fleet management aimed at reducing the environmental impact.

1. Summary

Thank you very much for taking the time and effort to thoroughly review this manuscript. We sincerely appreciate your valuable feedback, which has allowed us to improve the clarity and quality of our work. Below, you will find detailed responses to each of your comments, along with the corresponding corrections highlighted in yellow in the re-submitted files. We hope these revisions meet your expectations and further enhance the contribution of this research.

2. Questions for General Evaluation

Reviewer’s Evaluation

Response and Revisions

Is the content succinctly described and contextualized with respect to previous and present theoretical background and empirical research (if applicable) on the topic?

Can be improved

We have added some references relevant to the study to better contextualize the research.

Are the research design, questions, hypotheses and methods clearly stated?

Can be improved

Thank you for noticing. We hope the corrections made have improved the research design.

Are the arguments and discussion of findings coherent, balanced and compelling?

Can be improved

Thank you, We have enhanced the coherence in the results and discussion section.

For empirical research, are the results clearly presented?

Can be improved

We have added information to improve the presentation of the results.

Is the article adequately referenced?

Must be improved

Thank you for your comment. We have added some references to improve this point.

Are the conclusions thoroughly supported by the results presented in the article or referenced in secondary literature?

Can be improved

The conclusions are organized by indicator and conclude with a general summary, ensuring clarity and maintaining a logical order.

3. Point-by-point response to Comments and Suggestions for Authors

Comments 1: More literature reviews on the impact of maritime industry's emission on greenhouse gas emissions management could be added.

Response 1: Thank you for your feedback. We agree with the point you raised, which is why we have added four new references to better explain the research context. These references can be found from number 200 to 217 on page 5.

Comments 2: More detailed description of the quality control measures during data collection and processing to ensure the accuracy and reliability of the data.

Response 2: Agree. Accordingly, we have revised the methodology and added a paragraph on page 7, line 280 of the manuscript, to emphasize the data quality. This information was reviewed by the company prior to its use for research purposes."

Comments 3: Sensitivity analyses maybe could be conducted to assess the impact of different parameter changes on carbon intensity indicators and to enhance the robustness of the study.

Response 3: We completely agree with your observation; thank you for pointing it out. What you mentioned is already planned for a second stage, where tugboats with different propulsion technologies (electric, hybrid, and alternative fuels) will be included, and a sensitivity analysis will be conducted to empirically strengthen these conclusions.

Comments 4: This section is well written. However, the statistical graphs in this section need to be further embellished to better present the data and provide a better look and feel.

Response 4: We appreciate you pointing out this issue. We have updated all scatter plots by removing the brackets from the Y-axis and the vertical lines, aiming to enhance the visual experience for readers.

Comments 5: The logical structure of this section could perhaps be further optimized, e.g., by presenting the findings of the study in several different areas, which might make the conclusions clearer and more salient.

Response 5: Thank you for your feedback. Since this research focuses on carbon intensity indicators, the conclusions are structured around each of the analyzed indicators, which we have categorized as distinct 'areas' to provide greater clarity and organization

4. Response to Comments on the Quality of English Language

Point 1: English expression is relatively good, there is no reading difficulty, you can pay attention to the correct expression of technical terms.

Response 1: A review of the technical terms was conducted with the company's engineering team, and no errors were identified. However, if there is a specific term that requires closer attention, we are open to working on a suitable technical synonym.

1. Summary

Thank you very much for taking the time and effort to thoroughly review this manuscript. We sincerely appreciate your valuable feedback, which has allowed us to improve the clarity and quality of our work. Below, you will find detailed responses to each of your comments, along with the corresponding corrections highlighted in yellow in the re-submitted files. We hope these revisions meet your expectations and further enhance the contribution of this research.

2. Questions for General Evaluation

Reviewer’s Evaluation

Response and Revisions

Is the content succinctly described and contextualized with respect to previous and present theoretical background and empirical research (if applicable) on the topic?

Can be improved

We have added some references relevant to the study to better contextualize the research.

Are the research design, questions, hypotheses and methods clearly stated?

Yes

Are the arguments and discussion of findings coherent, balanced and compelling?

Can be improved

Thank you, We have enhanced the coherence in the results and discussion section.

For empirical research, are the results clearly presented?

Can be improved

We have added information to improve the presentation of the results.

Is the article adequately referenced?

Yes

Are the conclusions thoroughly supported by the results presented in the article or referenced in secondary literature?

Can be improved

The conclusions are organized by indicator and conclude with a

3. Point-by-point response to Comments and Suggestions for Authors

Comments 1: Clarification of Terms (Lines 9, 41):

The manuscript references “SAAM” towage fleet and “PAS 2060” without providing their full meanings or definitions. Determining these terms upon first mention in the text is essential for clarity.

Response 1: Thank you for pointing this out; you are absolutely right. For this reason, we have clarified the meaning of each of these abbreviations. However, since they do not form an acronym, we have explained their references, providing context in lines 41 and 125, on pages 2 and 3, respectively.

Comments 2: Literature Review:

While the manuscript reviews the framework of the International Maritime Organization (IMO), it lacks a comprehensive review of similar studies in the field. Including a detailed literature review would provide valuable context, highlight the novelty of the work, and position the study within the broader body of research on carbon intensity indicators and GHG management for harbor tugboats.

Response 2: Thank you for your comment. You are right; a detailed literature review is essential. However, this study focuses on carbon intensity indicators specifically for tugboats. Since there is limited literature available for this type of vessel, much of the reference material relies on the guidelines provided by the International Maritime Organization.

Comments 3: Data Representation (Lines 240–242, 248–253):

The data and findings presented in these sections would benefit from being represented in tabular or graphical formats. 

Response 3: Excellent suggestion. We have included a table that enhances the reader's experience when reviewing this data. It can be found at line 279, serving as a summary of the previous paragraph.

Comments 4: Supplementary Data:

The study would be significantly strengthened by presenting the data as supplementary data to provide more details about the analysis. Specifically: 

• Information about the number of tugboats in each category.

• The raw data used for the scatter graph and other analyses.

Response 4: The supplementary information you mentioned is confidential to the company and, therefore, cannot be included as an annex or shared with other readers. Nevertheless, we appreciate your comment as it allows us to clarify this point.

Comments 5: Fuel Type and Emission Factors (Lines 297–298):

The manuscript mentions specific emission factors but does not specify the type of fuel used by the tugboats that corresponds to these factors. Since emission factors are fuel-dependent, explicitly stating the type of fuel is crucial to ensure the results are interpretable and accurate.

Response 5: We greatly appreciate you pointing this out. We have now included the specification of the fuel used, which aligns with the emission factors mentioned in the document. This addition can be found on line 324.

Comments 6: Interpretation of Results:

While the results are presented and explained, the discussion lacks sufficient interpretation regarding how these findings apply to the study. 

Response 6: We are pleased that you mentioned this point. We have taken your suggestion into account and added two paragraphs in the results section to enhance the clarity of the information presented. The first paragraph appears between lines 554 and 556 on page 18, while the second spans lines 580 to 586 on page 19.

Comments 7: Figures 3, 5, 7, and 9

The manuscript refers to “ID Tugboat” in these figures, but it is unclear what “ID Tugboat” represents. 

Response 7: To improve the understanding of the manuscript, we clarified the meaning of "ID Tugboat," which essentially serves as an identifier to avoid filling the X-axis with the names of each tugboat. Additionally, it helps safeguard the confidentiality of the results presented in the graphs for each vessel. This explanation can be found in line 431 on page 12.

Comments 8: Discussion of Limitations:

Acknowledging limitations will enhance the integrity of the research and provide valuable context for interpreting the results. It will also help readers understand the broader implications and potential areas for future research.

Response 8: Thank you for the suggestion. We have made the change in the manuscript by adding a paragraph that discusses the limitations of the study. In this section, we outline certain guidelines that can be followed to further deepen the research, with the expectation that they will complement the conclusions presented here. This new paragraph was included at the end of the conclusions, from line 626 on page 19 to line 631 on page 20.