Investigation of the Viability of Unmanned Autonomous Container Ships under Different Carbon Pricing Scenarios
Piotr Tworek
Round 1
Reviewer 1 Report
Review of: “Investigation of the viability of unmanned autonomous container ships under different carbon pricing scenarios”
I found this paper rather interesting. I enjoyed reading it, and learned a lot. I particularly enjoyed the very nice writeup in Section 2.2 on container shipping (lines 150-198) which made the paper very useful. I want to thank the authors for writing such a great section; I will definitely reference that section in the future in my own work.
At the same time, there are some notable areas that could be improved. Mostly, this paper under review did a great job up through line 198 where it was discussing previous work, but began to get weaker starting in Section 3.
Finally, Figure 11 pretty clearly shows that the ONLY thing that matters here is fuel cost. The authors should make that clearer, and then show the results in a new FIGURE 12 where it is the DIFFERENCE between Conventional and Autonomous in each graph.
This paper needs more analyses:
First, a major point comes at line 239, where the authors should add a number of additional analyses showing what the sensitivity of their results are to the 40% assumption. What if that number varies by ship? What would be the “breakeven” reduction number for each type of ship where autonomous and not would be equal? Surely the cost of the crew quarters (as a percentage of fuel) would vary by the size of the ship if the ship were autonomous? So why not show a table where this percentage varies and show how it affects the results? That way, the reader might look at a small ship but with 50% reduction and a large ship with a 20% reduction (or the other way around) and decide for themselves.
Second, at line 245 the authors add the cost of emissions. How would the results change with and without the emissions issue? Again, isn’t this just basically determined by the 40% assumption above? My feeling is that all that is happening is that “annual fuel consumption cost” is being increased by a constant factor that is the “annual emission cost” as the only place emissions come from here is from fuel. Then, the cost savings is really related to the cost of fuel, which can be calculated with and without a cost of emissions.
Since fuel costs are highly variable, this seems like the entire paper devolves to how much the costs vary based on the price of fuel (either narrowly defined or more broadly defined if the emissions cost is included) and how much the percentage varies. These additional sensitivity tests (different percentages and estimates with varying fuel costs and estimates with and without emission costs) should also be analyzed and shown.
In addition, there are some methodology issues. The biggest issues relate to the TIME VALUE OF MONEY. Since Figures 4 and 5 suggests that prices vary over time, not all years are the same. What is the meaning of Emission costs in $/TEU later in the paper in figure 7 and fuel costs in Figure 8 if these costs vary across time? You cannot just AVERAGE them! Either you need to take a present value of all of these costs across time, or you need to pick a representative year or two. It is not at all clear that showing these changing costs across time is adding much; probably just showing the analyses for year 2030 and again for year 2050 would be sufficient as it seems unlikely that the larger inferences of whether conventional or autonomous would be better would differ greatly across these twenty years.
Similarly, Section 3.3 at lines 283 to 287 and equation 8 are just wrong. You cannot just add across years. So you cannot just take “average annual costs” and add it to “investment cost”. A smarter move might be to assess some kind of cost per year based on using an assumed cost of capital (say 10%) and just adding that to an individual year’s costs. Even better, the authors need to PRESENT VALUE the annual costs and add that to the investment cost (and then divide by TEU). The current method implicitly assumes the cost of capital (or the investment cost across time or the borrowing cost) is 0%, which is clearly not true anymore.
This issue about present valuing and doing things across years is highly relevant. Depending on the relative magnitude of the investment cost and the annual costs, these results could change completely. This is a typical capital budgeting question. There are many resources for the authors to learn about capital budgeting; see for example https://en.wikipedia.org/wiki/Capital_budgeting . The method the authors are trying to use here (incorrectly) is probably most equivalent to the “Equivalent Annual Cost” method described here: https://en.wikipedia.org/wiki/Equivalent_annual_cost . The authors should do that method if they want to continue the way they have been.
Finally, based on figure 11 and Table 3, I think the authors should make another short analysis of the differences between 13,900 and 18,270 TEU conventional and autonomous ships. Kind of a difference-in-differences analysis. The question of whether the larger ship is really better seems important; perhaps the 13,900 TEU ship is the sweet spot for autonomous ships. If so, that seems like an important result that needs to be demonstrated clearly and highlighted more.
Comments in order of line numbers:
Line 13: “ship exploitation”? I am not sure what “ship exploitation” means. Do you mean during the ship’s useful life?
Lines 38-40 and then 49 to 56: Can’t “human error” still come from any time something is “operated remotely” whether “from the shore or other ship”? It is not at all clear why human error would be reduced for autonomous ships if they are operated remotely – wouldn’t the same errors apply?
Line 79: I realize that SCC is defined in this line as “Shore Control Center” but I kept on looking for what “SCC” meant as I read the rest of the document. I don’t think this is such a common term that it is worth abbreviating. I would suggest that everywhere in the document it says “SCC” that the authors substitute “Shore Control Center” instead.
Lines 85 to 93: These five points were not immediately obvious to me and need a bit more introduction. Why would point 1 be true? Or point 2? Isn’t point 3 the same as point 1 – if there is less energy consumption, wouldn’t it make it greener? Probably these need a paragraph beforehand justifying these points, or at least these three points, before points 1-5 are brought up.
Line 144: “This paper proposed…” Which paper? This paper under review, or Jiang et al.? This sentence needs to be re-written, and get rid of “This” and instead say which paper you mean, which I think is Jiang but I am not sure. In fact, it looks like “This paper” is a typo and should just be deleted.
Line 239: Why was 40% chosen? See comment above
Line 244-245: Isn’t this just completely equivalent of adding a constant additional cost to the fuel cost (that is the cost of emissions)? Holding the price of bunker fuel per liter or gallon constant and the cost of CO2 constant, aren’t fuel costs and emissions costs perfectly correlated, so that these costs vary perfectly together per nautical mile? Lines 278 to 280 sure make it clear that this is true. See comments above.
Lines 278 to 280. See comments just above.
Lines 283 to 287: As mentioned above, this methodology is just wrong and doesn’t consider the time value of money across years. The methodology used here implicitly assumes that the interest rate (or, more accurately, cost of capital) is 0% for the next 25 years, which clearly is not the case. Instead, the authors should calculate the Equivalent Annual Cost (see https://en.wikipedia.org/wiki/Equivalent_annual_cost) and then divide THAT by the TEU to get RFR.
Line 314 to 319: Table 1 is nice and Figure 6 are nice. It is nice to see real ships and real routes.
Lines 320 to 324: These are very nice sentences and references. Thank you for putting them here.
Line 326: Table 2 would be more obvious (and easier to follow) if each column had the name of the ship on top like Table 1 did.
Lines 332-333: Is fuel consumption reduced by 10% or 40%? Is this 10% on top of the 40% described on line 239? Clearly I am confused and so more explanation is needed in the text.
Lines 334-335: First, I think you are missing the “[ ]” brackets around “60”. Second, why 110%? Please show if anything would vary if you used 100% or 125% or 150%.
Line 342-344: First, While Figure 7 is in color, many people might print out the paper (as I did) and then it just looks like grey bars. Can you make one color solid and another color dots or something other than solid so it looks different in black and white? Second, how about this figure being figure 7a, and figure 7b shows the DIFFERENCE between C and A? That is the real number that matters. Also, how can it be emission costs in $ if figure 4 vary per year? Read the comments above about recalculating everything using Equivalent Annual Cost
Line 356-357: Really only the fuel costs seem to matter based on Figure 11. Please recalculate everything not including CO2 costs (just use fuel costs) and show that pretty much you get the same results.
Line 363: Table 3 is great! Now do it NOT including CO2 costs. Pretty much the same % savings, isn’t it? (Also, of course, please fix RFR for Equivalent Annual Costs using the annuity smoothing method; see above.)
Line 374-375: What are “changes in freight rates” – what are “freight rates”? You are using “required freight rates (RFR)” as your variable, so things aren’t sensitive to “freight rates” but “required freight rates” are sensitive to changes in fuel costs. Also, “emission costs” seem no more sensitive than “capital, operating, and port parameters” here so really just fuel costs should be highlighted. However, if you were to make a Figure 11B which is the DIFFERENCE between the conventional and the autonomous lines (or add a third column of graphs which is the difference) then we can really see how much each line matters. Please do that.
Lines 378 to 411: Really, the major point is that RFR is lower for autonomous shipping and that how much it matters seems to be related to fuel costs.
Author Response
Our replies to all 5 Reviewers are given in the enclosed file.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Dear Editor,
The authors proposed an interesting study “Investigation of the viability of unmanned autonomous container ships under different carbon pricing scenarios”. The paper is well-structured and conveys a deal of information. I want to suggest a few suggestions to improve the manuscript quality and better readability.
1. The abstract can be improved by including the existing challenges, motivations and outcomes of the paper.
2. kindly add the description of the environment or carbon-related background in the introduction section. The following studies may help in improving the quality of this paper.
Impact of carbon pricing on distributed energy systems planning
Energy carbon emission reduction of China's transportation sector: an input–output approach
3.Also, the introduction must include the importance of this work can be highlighted at the end part.
4. Methods seem fine to me. However, the author(s) need to deep and systematic analysis about the results should highlight the novelty of this manuscript. Also, this part can be improved by comparing the study findings with previous studies.
5. The authors should increase policy recommendations aimed to articulate policy decisions.
6. Overall, the quality of English used in this study requires significant improvement.
Author Response
Our replies to all 5 Reviewers are given in the enclosed file.
Author Response File: Author Response.pdf
Reviewer 3 Report
Dear Authors,
Thank you for the opportunity to review your paper.
Let me start with the positive aspects:
· The language is appropriate.
· The abstract is well written - short and shows the essence of the text.
· The methodology is correctly written. The requirement for replicability of the study is ensured.
· The introduction is well written as it introduces the reader to the subject matter.
· Conclusions are also well written.
Notes on the rest of the text:
- You must indicate the source of the Figures. If the figures are prepared by yourself, you should note this.
- Rewrite this sentence:
Jiang et al. [32] This paper proposed, developed and tested a novel three-body 11,000 m rated autonomous and remotely-operated vehicle.
3. State the hypotheses or actual research questions separately.
Good luck.
Author Response
Our replies to all 5 Reviewers are given in the enclosed file.
Author Response File: Author Response.pdf
Reviewer 4 Report
Please revise the paper by addressing the following issues:
1. Introduction is too short. Introduction establishes the context of the research being conducted by summarizing current understanding and background information about the topic, stating the purpose of the work in the form of the hypothesis, question, or research problem, briefly explaining your rationale, methodological approach, highlighting the potential outcomes your study can reveal, and describing the remaining structure of the paper. Would you please reason both the novelty and the relevance of your paper goals?
2. In the Literature Review section, the authors provide many citations and related works. However, what is the research gap?
3. Is there any theoretical underpinning of the methodology used?
4. line 200: It’s figure 3 not 2.
5. A detailed discussion of your results with reference to existing literature is required.
6. The conclusion is pretty generic and fails to provide any improvement in the existing knowledge base. A conclusion is not merely a summary of your points or a re-statement of your research problem but a synthesis of key points. It offers new insight and creative approaches for framing/contextualizing the research problem based on the results of your study.
7. Please include practical implications of your study findings in the conclusion.
8. Limitations of the study should be discussed under separate heading.
9. Authors used so many abbreviations in the manuscript, it will be better if a list of abbreviations provided in the end of manuscript.
10. References require some revisions for uniformity in pattern according to the style recommended by the Journal.
11. Please proof read the manuscript before submitting the revision. See for example line 145.
Author Response
Our replies to all 5 Reviewers are given in the enclosed file.
Author Response File: Author Response.pdf
Reviewer 5 Report
The topic of the paper is interesting. In addition to theoretical considerations, it also includes a quantitative analysis carried out with the use of specific mathematical measures, which should be considered its strength. However, the final part of the publication is very weak. The parts related to the discussion and conclusions should be extended with the basic conclusions drawn from the considerations presented earlier. The last part of the paper (conclusion) seems to be too short. In the paper the following should be corrected: (1) the introduction does not precisely define the research gap based on a literature query conducted on the basis of internationally recognized and prestigious databases such as Scopus or Web of Science Core Collection; (2) in terms of the literature review, the text of the paper lacks a clearly defined key that would allow for a correct literature search. What keywords were chosen to make the right choice of literature? Was the selection made on the basis of abstracts or an analysis of the content of entire papers? These questions should be answered in the text of the paper; (3) in general, the results of analyses and theoretical considerations do not raise serious objections. In the central part of the paper, a bit more in-depth analysis and interpretation of the results should be made. In addition, the reader should be indicated what are the differences and similarities between the results of the authors' calculations and the existing research results, i.e., those published so far in the scientific literature; (4) the final part (conclusion) is a very weak part of the paper. The conclusions should thoroughly and clearly answer the question about the contribution of the research results presented in the paper to science. Next, it is necessary to underline what the implications of the presented results for the organizational practice are. This part of the paper may contain subsections, i.e., research input and implications for practice; (5) the paper should be proofread by a certified English translator. Nevertheless, applying all the corrections indicated in this review will allow the paper to be published in this journal. The review is positive. I emphasize once again that the paper may be published in this journal, provided that the comments contained in the review are taken into account and that the approval of the editor-in-chief is obtained.
Author Response
Our replies to all 5 Reviewers are given in the enclosed file.
Author Response File: Author Response.pdf
