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  • Alba Matínez-López1,*,
  • Héctor Rubén Díaz Ojeda1 and
  • Marcos Míguez González2
  • et al.

Reviewer 1: Giacomo Viccione Reviewer 2: Anonymous

Round 1

Reviewer 1 Report

The manuscript is well written, with a clear message delivered to the reader. The abstract gives the whole important points of the work done, however some results with key concrete values are missing. Literature review should be extended, comprehending more recent contributions. Adopted materials and methods should be better explained, results and related discussion are clearly given.

When paste your abstract, ensure the words are not truncated, e.g. “Ship-ping”, “Reyn-olds”, “op-timization”

The literature review seems not comprehensive. A broader discussion could be made by considering some up-to-date reports, e.g.:

Song et al. 2021. Experimental investigation on the effect of heterogeneous hull roughness on ship resistance, Ocean Engineering 223,108590, DOI: 10.1016/j.oceaneng.2021.108590

Abebe et al. 2020. Machine learning approaches for ship speed prediction towards energy efficient shipping, Applied Sciences (Switzerland) 10(7),2325, DOI: 10.3390/app10072325

2.3. Computational Fluid Dynamics (CFD) analysis

Please provide details about time stepping and adopted scheme to march in time.

LINE 368. The sentence is cut (carriage return pressed by mistake)

Thx for your gratitude, however I’m not sure it is orthodox mentioning us in the Acknowledgments. Do not forget giving the Authors contribution and funding statements as they are mandatory.

Check for the reference style, e.g., DOIs and page ranges given in different formats.

Author Response

Reviewer #1: The manuscript is well written, with a clear message delivered to the reader. The abstract gives the whole important points of the work done, however some results with key concrete values are missing. Literature review should be extended, comprehending more recent contributions. Adopted materials and methods should be better explained, results and related discussion are clearly given.

 

Thank you so much for supporting us to improve our work. Thank you for your time.

 

 

  1. When paste your abstract, ensure the words are not truncated, e.g. “Shipping”, “Reynolds”, “optimization”

 

Thank you for the comment. The body text has been reviewed and corrected with special attention to the truncated words.

 

 

  1. The literature review seems not comprehensive. A broader discussion could be made by considering some up-to-date reports, e.g.: Song et al. 2021. Experimental investigation on the effect of heterogeneous hull roughness on ship resistance, Ocean Engineering 223,108590, DOI: 10.1016/j.oceaneng.2021.108590; Abebe et al. 2020. Machine learning approaches for ship speed prediction towards energy efficient shipping, Applied Sciences (Switzerland) 10(7),2325, DOI: 10.3390/app10072325In

 

Thank you for the references. The papers’ results were included in the analysis and conclusions (lines 397-399, lines 469-470).

 

 

  1. 3. Computational Fluid Dynamics (CFD) analysis. Please provide details about time stepping and adopted scheme to march in time.

 

The reviewer can find information about the time step in the table 2, additionally we have included an explanation about the numerical scheme used: PISO algorithm (please see lines 172- 173). In line 178 the turbulence model for the simulation is also introduced in such a way that, the equations are solved by using PISO algorithm and the turbulence model. Finally, VOF use (see line 174- 177) is included for solving the free surface problem in this work. We hope to accomplish so the reviewer’s comment.

 

  1. LINE 368. The sentence is cut (carriage return pressed by mistake)

 

Done. Really, it was a mistake. Thank you.

 

  1. Thx for your gratitude, however I’m not sure it is orthodox mentioning us in the Acknowledgments. Do not forget giving the Authors contribution and funding statements as they are mandatory.

 

Dear reviewer we are fully aware of the time invested by the reviewers to improve our work and we are really thankful, so it is not just orthodox to recognize your task in the acknowledges but also fair.

Thank you for reminding the inclusion of our sponsors (done!).

 

  1. Check for the reference style, e.g., DOIs and page ranges given in different formats.

We have reviewed the format of the reference section. Thank you.  

Reviewer 2 Report

The paper addresses three resistance prediction methods for vessels dedicated to an optimization problem for shipping route velocity and gas exhaust emissions. The authors present in a clear manner the three methods and formulate the optimization problem in a useful way for environmental considerations. The paper concludes about the three models capabilities for predicting shipping aerial pollution. The research presented follows the best standard and the paper could be accepted after following some recommendations/suggestions given here after.

Science

The shipping route analysed (Vigo-St Nazaire) crosses the cap Finisterre where 45°swell can append during winter season. Here, the paper could explain more in details several hypotheses about an investigation independent of meteorological conditions, sea states. It can be underlined also the independence of the investigation with freight mass and goods moored on the ship who can affect the ship draught and consequently the ship resistance. It can be underline that the investigation is made without the interview of ship captain and shipping companies about the real fuel consumption (to be compared with the computed one). The paper could present in a better way the manoeuvre phase in the harbour, because ship consumes oil at quay for commercial operations. In that purpose, the electrification at quay permits to reduce the gas emission and it may be outside the paper scope.

Edition

 t is tons line 106

Usually we see the Froude number with Fr and not Fn, may be explained

Check section 2.4, equations number (4) is div u=0

GWP could be presented

Time step (s) units Table 2

Typos

., line 95

]is line 170

.This line 178

Being positive line 336

(with line 343

Edit line 369

Edit refs 7 8 11 17 20 30 34

Convergences line 274

Author Response

Reviewer #2: The paper addresses three resistance prediction methods for vessels dedicated to an optimization problem for shipping route velocity and gas exhaust emissions. The authors present in a clear manner the three methods and formulate the optimization problem in a useful way for environmental considerations. The paper concludes about the three models capabilities for predicting shipping aerial pollution. The research presented follows the best standard and the paper could be accepted after following some recommendations/suggestions given here after.

 

Dear reviewer, thank you so much for accepting to review our work. Thank you so much for your time.

Science:

  1. The shipping route analysed (Vigo-St Nazaire) crosses the cap Finisterre where 45°swell can append during winter season. Here, the paper could explain more in details several hypotheses about an investigation independent of meteorological conditions, sea states.

Thank you for your comment. The scope of the current paper is assessing the environmental consequences of applying several resistance prediction methods under calm water conditions for optimization of vessels. Even though the results achieved regarding the methods performance (accuracy level among methods) are valid regardless of waves effects, the overall environmental costs will be increased in all cases when the waves effect is considered. Indeed, the waves effect on the vessel´s resistance is relevant, and it is a ‘’pending task’’ in this work. This is collected in the further research lines of the paper, concretely in the last paragraph of the paper (conclusions), where the need of a joint assessment for a particular route (sea state) and vessel (technical and operative features) is delighted.   

  1. It can be underlined also the independence of the investigation with freight mass and goods moored on the ship who can affect the ship draught and consequently the ship resistance.

Thank you for your comment. This paper is framed in the context of SSS vessels optimization and the operative research of them. By default, the resistance is analyzed under summer draught conditions (design load draught condition) to optimize the vessels in the design phase. Obviously, the load conditions of a vessel are numerous and indeed affect to their resistance through their draught. However, this work assumes identical conditions (summer draught as design draught) for all methods evaluated to establish a realistic comparison among them. Different draughts will expectedly lead to different total results but the relative performance among methods should be the same.

To address this comment, we have detailed this assumption for the analysis of the application case section: line 237 and 240.

  1. It can be underline that the investigation is made without the interview of ship captain and shipping companies about the real fuel consumption (to be compared with the computed one).

Well, we agree with the reviewer and in fact the fuel registration is required by the current legislation (compulsory from 2019, MEPC.278(70)and resolution MEPC.349(78)) for the built vessels….so, it is interesting and feasible to consider real data to test prediction models of resistance based on real vessels.

However, this paper analyzes the environmental consequences of optimizing a vessel in the design phase (not built yet) based on low accuracy resistance prediction methods. After this step, when the preliminary design was already selected, tank tests valid the resistance obtained through numerical methods prediction before its construction and, the power curve is finally verified in sea trials (full scale ship in open water test) when the vessel is built. However, the features’ selection of the vessel and its operative performance estimation were carried out before its construction. 

 

  1. The paper could present in a better way the manoeuvre phase in the harbour, because ship consumes oil at quay for commercial operations. In that purpose, the electrification at quay permits to reduce the gas emission and it may be outside the paper scope.

The paper assumes as a maneuvering stage the time from arriving at the Port area (Fairway Buoy) to the berth, by excluding so the berthing time (mooring and loading/unloading operations), since in the latter, there is not advance resistance for the vessel (main engines are not operating).

We agree with the reviewer, on shore power supply (OPS) during the berthing time involves significant environmental advantages for SSS in regions where the electric network has a high RES (renewable energy sources) share.

In order to attend this comment we have argued the exclusion of the berthing stage for the analysis in lines 185-188 and clarified the manouverig stage meaning (lines 194-195). Additionally, we have included the potential advantage of OPS for SSS by considering previous findings in this regard [188-190].

Edition

  1. t is tons line 106

Done!

  1. Usually we see the Froude number with Fr and not Fn, may be explained

Both expressions are valid (at least from our experience), so we have changed it to Fr to implement the comment.

  1. Check section 2.4, equations number (4) is div u=0

Thank you for the comment. In the Eq 4, the div u is expressed through  where the sub index “f” only means the use of a fluid (in this problem could be water or air). This is in line with Fluid Mechanics 8th Edición by Frank White (among other books).

  1. GWP could be presented….

We are not sure to understand this comment completely….the last paragraph before section 3 collects the methane emissions impact through its GWP (line 227) , additionally CO2 = 1 GWP….however both values together do not offers the overall GWP of the vessel trip… since other emissions (that were not assessed by this model) contribute to GWP of the vessel. For this reason, the CO2 and CH4 are shown in a desegregated mode in the figure 4…we are not sure if the reviewer is referring to this…

  1. Time step (s) units Table 2

Done. Thank you

Typos:

., line 95

]is line 170

.This line 178

Being positive line 336

(with line 343

Edit line 369

Edit refs 7 8 11 17 20 30 34

Convergences line 274

The typos were solved and the bodytext reviewed. Thank you