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Peer-Review Record

Study of Hybrid Propulsion Systems for Lower Emissions and Fuel Saving on Merchant Ship during Voyage

J. Mar. Sci. Eng. 2022, 10(3), 393; https://doi.org/10.3390/jmse10030393

by Cheng Siong Chin^1,*

, Yan-Jie Tan¹ and Mohan Venkatesh Kumar²

Reviewer 1: Anonymous

Reviewer 2: Anonymous

Reviewer 3:

Taek-Kun Nam

J. Mar. Sci. Eng. 2022, 10(3), 393; https://doi.org/10.3390/jmse10030393

Submission received: 11 January 2022 / Revised: 4 March 2022 / Accepted: 7 March 2022 / Published: 9 March 2022

(This article belongs to the Section Ocean Engineering)

Round 1

Reviewer 1 Report

Starting from the fuel consumption, emissions and fuel quality of two-stroke diesel engines, which are commonly used power sources for large intercontinental commercial ships, and considering the latest emission regulations and carbon reduction measures, the author studied the effects of transient characteristics of two-stroke engines on marine fuel consumption, emissions and efficiency, as well as feasibility analysis such as configuring a reasonable battery for power peak regulation.

This is a topic of interest to researchers in the marine battery field, but the paper requires certain revisions before it can be accepted for publication. My detailed comments are as follows:

1. The graphs in the paper lack legends (Fig. 1, Fig. 3, Fig. 4), and it is recommended to have corresponding legends or emoticons for arrow directions, solid and dashed lines;
2. The FastSeas website is mentioned in the text , please describe the necessity of using this weather navigation tool;
3. The battery peak shaving is mentioned in 7.3, but there is no content related to the peak shaving strategy，which is the embodiment of the peak shaving method and generator work instructions , the energy storage object for peak shaving is batteries, and the response characteristics of batteries during peak shaving are not shown in the paper, which is a major defect of this research;
4. Section 6 of the article excessively describes lithium batteries, lead-acid batteries, Compared with batteries such as nickel-metal hydride, there is less content for the targeted configuration design of the target ship, please adjust the content of this section.

Author Response

Dear Professor,

We would like to resubmit the paper for publication. We have made the required changes as suggested by the reviewers. The entire paper was proofread.

We sincerely hope you can give this paper a fair review and provide an opportunity for publication.

We confirm that neither the manuscript nor any parts of its content are currently under consideration or published in another journal.

All authors have approved the manuscript and agree with its submission to Journal of Marine Science and Engineering.

Thank you very much.

Yours Sincerely,

Authors

Reviewer #1

This is a topic of interest to researchers in the marine battery field, but the paper requires certain revisions before it can be accepted for publication. My detailed comments are as follows:

The graphs in the paper lack legends (Fig. 1, Fig. 3, Fig. 4), and it is recommended to have corresponding legends or emoticons for arrow directions, solid and dashed lines;

Reply: Noted. We have revised Figure 1, 3 and 4 by including the arrow direction indicating whether it is mechanical link, electrical link or possible sense of energy.

The FastSeas website is mentioned in the text , please describe the necessity of using this weather navigation tool;

Reply: Noted. We have included the reason for the use of FastSeas. Frankly, there are few software such as Maritime Route Planning Logistic Software - Sinay. But we have chosen FastSeas as it is open source and easy to use. FastSeas is a weather routing tool to compute the quickest route from point A to point B given the information from the current National Oceanic and Atmospheric Administration(NOAA) Global Forecast System (GFS) weather forecast and current oceanic currents.

The battery peak shaving is mentioned in 7.3, but there is no content related to the peak shaving strategy，which is the embodiment of the peak shaving method and generator work instructions , the energy storage object for peak shaving is batteries, and the response characteristics of batteries during peak shaving are not shown in the paper, which is a major defect of this research;

Reply: Noted. The peak shaving strategy is as follows. The battery is charged when the measured power consumption is less than the target peak demand setpoint. When the measured power consumption is greater than the setpoint, the battery is discharged. As the operation of the ship and battery changes, the target peak demand setpoint changes. The battery enables the engine to operate at an average load (see average curve), charging the battery at its lowest, and discharging at its peaks. As seen in Figure 6, both curves represent similar energy consumption. The peak of the actual curve increases the fuel consumption. Peak shaving decreases the overall energy consumption for the dynamic loads such as thrusters or crane operations. In this study, the MAN energy solution provided a maximum of 5% saving due to the peak shaving.

Section 6 of the article excessively describes lithium batteries, lead-acid batteries, Compared with batteries such as nickel-metal hydride, there is less content for the targeted configuration design of the target ship, please adjust the content of this section.

Reply: Noted. In this study, the battery is arranged in the parallel configuration as shown with (at least) two engines (see Figure 5 of the revised paper). One engine is running at 80%, and during the voyage, one auxiliary engine can cover the load while the second be under maintenance due to unforeseen engine fault. On the other hand, the battery can buffer such unexpected cases and optimize the engine's fuel consumption via peak load shaving operation.

Author Response File: Author Response.pdf

Reviewer 2 Report

Dear authors,

Your manuscript entitled: "Simulating Hybrid Propulsion Systems on Bulk Carrier for Sea Route"

refers to a very actual issue related to the search for various methods of reducing air pollution, especially the limits of carbon dioxide, NOx and SOx. In the manuscript, you discuss how to lower the air pollution generated by a two-stroke slow-speed engine used on seagoing vessels. The different analysis were carried out on the basis of parameters of real ship type bulk carrier equipped in real two stroke engine. The analysis were done for two routes.

And it is very important. The manuscript do not presented simulation of any hybrid propulsion system.

I appreciate the various analyses presented, but they are not simulations of hybrid propulsion systems. Additionally, the manuscript has some small errors, and is careless in details.

The manuscript can be accepted but under same conditions:

The title have to correspond to the presented issues.
The manuscript should be corrected to be more clear and comprehensible.
Only some samples of many different errors or inconsistencies are given that need to be corrected:

Row :

Figure 1. lack of electric motor/shaft generator for requirement of PTO/PTI, proper numbering of the gensets. Explanation of directions and meaning of arrows.

probably more convenient caption after correction of drawing: “Example of hybrid propulsion configuration”

102

Table1

Row 9: value of BHP; probably should be 7355 kW not 0.7355 kW

Row 11: value of Power: 9660 kW not 9660kW (space between number and unit). Such an editing error is frequent later in the text. All such errors should be corrected.

116

What is this equation for. The sentence in line 114 shows that it is used to calculate LWL !!!!, it is actually used to calculate Vhull. But it is strange that the speed is calculated using such a formula. What's the number 1.34? What about units?

120

Table 2. Route 1 from Australia to China; inside the table are data for two routs!

142

Something wrong with equation 2

149

What does mean ∑MCR?

The symbol “∑” is used some time in other places without explanation!

“g/kwh” should be: “g/kWh”.

A similar problem exists elsewhere where capital letters are converted to lower case and vice versa.

Why there is used unit for one parameter but others without?

155

Table 3. Emission factor for slow speed engine

Should be: factors.

First row of table: there are units with no names possibly factors!

159/160

The statement: ”… four-stroke medium-speed engine working as auxiliary generators to supply the hotel load.” is not true.

176

“Figure 3. Series hybrid configuration” should be on the same pages as drawing.

Maybe better will be: Series hybrid propulsion configuration.

180

The drawing is too simplistic. No propeller. What does systems mean?

181

Maybe better will be: Parallel hybrid propulsion configuration.

198

Table 5. Row 4. (Wh/L) probably should be (Wh/l)

200-210

Not all battery types in Table 5 are covered.

233-236

It is not clear what about the authors' intention.

In this section, the authors should include drawings that will illustrate the proposed modification of the propulsion system. It is interesting how the conventional two-stroke engines commonly used by large bulk carriers will be supported by battery power system.

Overall, section 7 as a whole is unclear. There are many simplifications without explanation.

255, 256, 257

Calculations in this form are unnecessary and should be deleted.

Similar situation concern rows: 266, 267, 269, 270, 272, 273, 326,333, 334, 361, 362, 370, 398, 399, maybe also others.

292

Full words in the equation should be avoided.

Symbols are commonly used in the equation, which need to be described later. It concern many other equations.

339/340

Lack of reference to “…the guidelines published by the IMO,”

343/344

The sentence: “As seen in Table 13, the vessel with overall length of 228.99m gives a significant wave height of 4m and mean wind speed of 15.7m/s.” is not clear in reference to the other texts.

353

Lack of reference to the equation (20). What does mean ∑R_wind?

357

What does mean ∑R_waves?

354

(KN) or (kN)?

387

Table 15,

Without additional data the table is unclear.

Propulsion energy- it is just the fuel oil energy used by Main Engine?

Hotel energy-it is only fuel oil energy spent to supply hotel (in marine industry it is named accommodation).

What about electrical energy generated for supplying auxiliary systems necessary for running the main engine and other equipment as ruder machinery, navigation ect.

391

Form of Equation (25) is not acceptable. Fuel Cost of what oil: HFO or FO (Heavy Fuel Oil or light Fuel Oil ). Ships used different fuel oil depends of sailing mode. During manoeuvring mode ships used light Fuel oil but during deep see sailing ships used only HFO. This aspect was not taken under consideration calculated cost of fuel and additionally by estimating of different aspect of air pollution.

394

Form of Equation (26) is not acceptable: full words!!!

There is mess in the nomenclature: Cost, cost of maintenance and Maintenance !!!!!

401

Lack of reference

Remarks to the References:

There are ONLY 8 items where 5 is a website. There only three websites were available !!!

Surprisingly, hybrid propulsion systems are a very current issue and there are many scientific papers available. The lack of reference in this regard translates into a very low quality of the manuscript.

Comments for author File: Comments.pdf

Author Response

Dear Professor,

We would like to resubmit the paper for publication. We have made the required changes as suggested by the reviewers. The entire paper was proofread.

We sincerely hope you can give this paper a fair review and provide an opportunity for publication.

We confirm that neither the manuscript nor any parts of its content are currently under consideration or published in another journal.

All authors have approved the manuscript and agree with its submission to Journal of Marine Science and Engineering.

Thank you very much.

Yours Sincerely,

Authors

Reviewer #2

The analysis were done for two routes.

And it is very important. The manuscript do not presented simulation of any hybrid propulsion system. I appreciate the various analyses presented, but they are not simulations of hybrid propulsion systems. Additionally, the manuscript has some small errors, and is careless in details.

The manuscript can be accepted but under same conditions:

The title have to correspond to the presented issues.

Reply: Noted. We have revised the title to: Study of Hybrid Propulsion Systems for Lower Emission and Fuel-Saving on Merchant Ship during Voyage

The manuscript should be corrected to be more clear and comprehensible.

Reply: Noted. We have revised the manuscript to be more clear and comprehensible.

Only some samples of many different errors or inconsistencies are given that need to be corrected:

Row :

Figure 1. lack of electric motor/shaft generator for requirement of PTO/PTI, proper numbering of the gensets. Explanation of directions and meaning of arrows.

Reply: Noted. We have revised Figure 1 by including the arrow direction indicating whether it is mechanical link, electrical link or possible sense of energy.

probably more convenient caption after correction of drawing Example of hybrid propulsion configuration

Reply: Noted. We have revised the figure caption.

102

Table1

Row 9: value of BHP; probably should be 7355 kW not 0.7355 kW

Reply: Noted. We have revised to 7355 kW.

Row 11: value of Power: 9660 kW not 9660kW (space between number and unit). Such an editing error is frequent later in the text. All such errors should be corrected.

Reply: Noted. We have revised all the errors.

116

Reply: Noted. The ship requires much greater power to accelerate beyond its hull speed, which is determined by the length of the waterline and can be calculated using the formula: Vmax (in knots) = square root of LWL (in feet) x 1.34. The hull speed is the speed at which the wavelength of the bow wave stretches out to the length of the waterline.

120

Table 2. Route 1 from Australia to China; inside the table are data for two routs!

Reply: Noted. We have revised the caption to “Routes from Australia to China and Japan”

142

Something wrong with equation 2

Reply: Noted. We have revised the equation 2.

where EF is the emission factor; fuel is the fuel consumption; Sulphur content depends on fuel; fuel is the fuel consumption. The number 2 refers to the pounds of sulphur dioxide per pound of sulphur. In this case, the sulphur content of 2.7% is used.

149

MCR?

Reply: Noted. MCR is the Maximum continuous rating of the engine. It is the maximum power output engine can produce while running continuously at safe limits and conditions. It is specified on the engine nameplate and in the Technical File of the marine diesel engine

in other places without explanation!

Reply: Noted. We have checked the entire paper for any missing acronym explanation.

A similar problem exists elsewhere where capital letters are converted to lower case and vice versa. Why there is used unit for one parameter but others without?

Reply: Noted. We have checked and revised the entire paper.

155

Table 3. Emission factor for slow speed engine Should be: factors.

First row of table: there are units with no names possibly factors!

Reply: Noted. We have checked and revised Table 3.

159/160

The statement: " ... load." is not true.

four-stroke medium-speed engine working as auxiliary generators to supply the hotel

Reply: Noted. We have revised the sentence.

176

Figure 3. Series hybrid configuration" should be on the same pages as drawing.

Maybe better will be: Series hybrid propulsion configuration.

Reply: Noted. We have revised the figure caption.

180

The drawing is too simplistic. No propeller. What does systems mean?

Reply: Noted. We have revised the figure to include the propeller.

181

Maybe better will be: Parallel hybrid propulsion configuration.

Reply: Noted. We have revised the figure caption.

198

Table 5. Row 4. (Wh/L) probably should be (Wh/l)

Reply: Noted. We have revised the unit.

200-210

Not all battery types in Table 5 are covered.

Reply: Noted. We would like to include the common types of batteries used.

233-236

It is not clear what about the authors' intention.

Overall, section 7 as a whole is unclear. There are many simplifications without explanation.

Reply: Noted. We have provided the proposed parallel configuration of hybrid battery system in Figure 5.

255, 256, 257

Calculations in this form are unnecessary and should be deleted.

Similar situation concern rows: 266, 267, 269, 270, 272, 273, 326,333, 334, 361, 362, 370, 398, 399, maybe also others.

Reply: Noted. We have removed all the unnecessary working.

292

Full words in the equation should be avoided.

Symbols are commonly used in the equation, which need to be described later. It concern many other equations.

Reply: Noted. We have shortened the name of the equations.

339/340

Lack of reference to " ... the guidelines published by the IMO,"

Reply: Noted. We have included the reference by IMO GHG Emissions. Available online: http://www.imo.org/en/OurWork/Environment/PollutionPrevention/AirPollution/Pages/GHG-Emissions.aspx

343/344

The sentence: "As seen in Table 13, the vessel with overall length of 228.99m gives a significant wave

height of 4m and mean wind speed of 15.7m/s." is not clear in reference to the other texts.

Reply: Noted. The wave height and mean wind speed are obtained from the adverse weather condition in the following references. We have cited the references.

MSC 93/21/5 (2014) Safety evaluation of the interim guidelines for determining minimum propulsion power to maintain the manoeuvrability of ships under adverse weather conditions, submitted by Greece
Shigunov, V. Manoeuvrability in adverse conditions: rational criteria and standards. J Mar Sci Technol 23, 2018, pp. 958–976.

353

Lack of reference to the equation (20). What does mean wind?

Reply: Noted. It refers to mean wind speed.

357

What does mean IRwaves?

Reply: Noted. We have revised the symbol. It refers to resistance caused by waves.

354

(KN) or (kN)?

Reply: Noted. We have made the change to kN.

387

Table 15,

Without additional data the table is unclear.

Propulsion energy- it is just the fuel oil energy used by Main Engine?

Reply: Noted the data can be found in https://www.man-es.com/docs/default-source/marine/tools/batteries-on-board-ocean-going-vessels.pdf?sfvrsn=deaa76b8_12 . We have added the reference.

Hotel energy-it is only fuel oil energy spent to supply hotel (in marine industry it is named accommodation).

What about electrical energy generated for supplying auxiliary systems necessary for running the main engine and other equipment as ruder machinery, navigation ect.

Reply: Noted. We have revised the sentence.

391

Reply: Noted. We assumed the cost of heavy fuel oil for sailing as it dominates the cost of the entire voyage.

394

Form of Equation (26) is not acceptable: full words!!!

There is mess in the nomenclature: Cost, cost of maintenance and Maintenance !!!!!

Reply: Noted. We have shortened the words to “Main_cost”

401

Lack of reference

Remarks to the References:

There are ONLY 8 items where 5 is a website. There only three websites were available !!! Surprisingly, hybrid propulsion systems are a very current issue and there are many scientific papers available. The lack of reference in this regard translates into a very low quality of the manuscript.

Reply: Noted. We have included 9 more references.

Bennabi, N., Charpentier, J.F., Menana, H., Billard, J.Y. & Genet, P. (2016) Hybrid propulsion systems for small ships: Context and challenges. Proceedings - 2016 22nd International Conference on Electrical Machines, ICEM 2016. (October 2018), 2948–2954.
Achilleas Grigoriadis, Sokratis Mamarikas, Ioannis Ioannidis, Elisa Majamäki, Jukka-Pekka Jalkanen, Leonidas Ntziachristos, Development of exhaust emission factors for vessels: A review and meta-analysis of available data, Atmospheric Environment: X, Volume 12, 2021, 100142.
Zakeri, B. & Syri, S. (2015) Erratum: Electrical energy storage systems: A comparative life cycle cost analysis ( Sustain. Energy Rev. (2015) 42 (569-596)). Renewable and Sustainable Energy Reviews. 531634–1635.
Omer Berkehan Inal, Jean-Frédéric Charpentier, Cengiz Deniz, Hybrid power and propulsion systems for ships: Current status and future challenges, Renewable and Sustainable Energy Reviews, Volume 156, 2022, 111965.
Yang, R.; Yuan, Y.; Ying, R.; Shen, B.; Long, T. A Novel Energy Management Strategy for a Ship’s Hybrid Solar Energy Generation System Using a Particle Swarm Optimization Algorithm. Energies 2020, 13, 1380.
Kim, S.; Kim, J. Optimal Energy Control of Battery Hybrid System for Marine Vessels by Applying Neural Network Based on Equivalent Consumption Minimization Strategy. Mar. Sci. Eng. 2021, 9, 1228.
Bennabi, N.; Menana, H.; Charpentier, J.-F.; Billard, J.-Y.; Nottelet, B. Design and Comparative Study of Hybrid Propulsions for a River Ferry Operating on Short Cycles with High Power Demands. Mar. Sci. Eng. 2021, 9, 631.
Litwin, W.; Leśniewski, W.; Piątek, D.; Niklas, K. Experimental Research on the Energy Efficiency of a Parallel Hybrid Drive for an Inland Ship. Energies 2019, 12, 1675.
Shigunov, V. Manoeuvrability in adverse conditions: rational criteria and standards. J Mar Sci Technol 23, 958–976 (2018)

Author Response File: Author Response.pdf

Reviewer 3 Report

This paper addresses the conventional propulsion system of large bulk carriers and the method of constructing a hybrid system that can utilize an electric power from batteries to the propulsion system. It also discusses the effects of applying these systems to ships operation, e.g. peak shaving, boosting for barred speed range and during adverse weather conditions. It is considered that the proposed system in the paper will have the advantage of reducing harmful emission gas as well as fuel consumption from merchant vessel.

However, to achieve these advantages, there must be a prerequisite that there is a hybrid system which can combine batteries with the existing propulsion system. Therefore, it would be desirable to configure the proposed hybrid system using components, i.e., battery and control device, etc. and present the necessary costs.

This is because even if the proposed method is applied to reduce fuel consumption and harmful exhaust gas, it is not expected to be easy to apply in merchant ships if the payback time is too long.

For detailed questions, please refer to the attached PDF file.

Comments for author File: Comments.pdf

Author Response

Dear Professor,

We would like to resubmit the paper for publication. We have made the required changes as suggested by the reviewers. The entire paper was proofread.

We sincerely hope you can give this paper a fair review and provide an opportunity for publication.

We confirm that neither the manuscript nor any parts of its content are currently under consideration or published in another journal.

All authors have approved the manuscript and agree with its submission to Journal of Marine Science and Engineering.

Thank you very much.

Yours Sincerely,

Authors

Reviewer #3

Comments for Authors:

This is because even if the proposed method is applied to reduce fuel consumption and harmful exhaust gas, it is not expected to be easy to apply in merchant ships if the payback time is too long.

Detailed questions about the paper are as follows.

If we consider the PTI in the Figure 1, please check if the arrow direction is correct.

Reply: Noted. We have revised Figure 1 with the correct arrow direction.

BHP 0.7355 kW seems to represent 1 PS in the Table 1. Readers need a definition of this in the table?

Reply: Noted. It is a typo mistake. It should be 7355 kW.

As mentioned earlier, it would be desirable to explain how to composite a hybrid system (series or parallel) considering each components, its cost, advantages and disadvantages.

Reply: Noted. The hybrid propulsion system provides greater redundancy, protection against uncertainty of future fuel cost, insurance against increasing environmental legislation, and noise reduction. Hybrid propulsion also allows for design flexibility as the vessel can be configured to help to balance between the economic constrain and the environmental advantage. However, hybrid propulsion is more complex and requires higher capital costs and knowledge capital. As hybrid propulsion system advances, maintenance and spare part procurement may pose an issue for the long term. We agreed that the hybrid propulsion system is not an option for some merchant ships if the payback time is too long.

Results in Eq (7) and Eq (8) could be understand as fuel consumption in each cylinder? The BP(brake power) in Eq (6) is derived as the value of each cylinder.

11, Line # 335~336

Reply: Agreed. It refers to each cylinder.

Since C rate is 120, the paper supposed that an additional power source different from C

rate 1 should be combined, but what power source can be selected from the ship? Power margin should be obtained by applying a battery-based hybrid system, and it is not well understand that an additional power source should be ensured again.

Reply: Noted. The hybrid battery system provides additional support for the conventional two-stroke propulsion engines. The battery enables the engine to operate at an average load, charging the battery at its lowest and discharging at its peaks. Peak shaving decreases the overall energy consumption for dynamic loads such as thrusters or crane operations. In addition, the boosting helps vessels during operations, such as providing extra power to reduce time spent in the barred speed range region and providing additional power during adverse weather conditions to help maintain the minimum speed requirement set by the IMO

Minutia:

p.12

T in Eq (21) means draught of ships. But, T is expressed as time duration in the overall paper, so it would be better to unify the definition of T .

Reply: Noted. We have revised the draught to “DT” instead of “T”

Line # 371, 82 dwt 82,000 dwt

Reply: Noted. We have revised 82 dwt to 82,000 dwt

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

I think the content of this revision has been greatly improved compared with the first draft. Details such as symbols and units have been displayed and modified, and existing problems have been supplemented in the current manuscript.

Author Response

Comment: I think the content of this revision has been greatly improved compared with the first draft. Details such as symbols and units have been displayed and modified, and existing problems have been supplemented in the current manuscript.

Reply: Thank you very much for the review.

Reviewer 2 Report

Dear authors,

Thank you very much for your cover letter.

First of all, you only sent the "Final: Show Markup" version for review, which is correct, but with all the revision markings it is difficult to estimate the final version. Therefore, it will be very useful to get both the "Final: Show Markup" and the "Final" versions. For the next round, please send me both versions and additionally the final version of the current manuscript.

If the Editorial Board has given you another chance for a review, please take my comments very seriously. This is your manuscript, not mine. The manuscript should be precise and very reader-friendly, and you should realize that the manuscript is a type of presentation of the results of a research work, not a story.

Therefore, despite the many corrections that have been made, the manuscript is still not ready for printing.

The title corresponds to the content of the manuscript
Not all comments have been taken into account without sufficient explanation or discussion, so it is difficult to recommend the manuscript for printing.

99 Previous: 92

The two-stroke main engine runs on fuel. To use electricity for the propulsion system in the above very general case, it is necessary to add element(s) that convert electrical energy into mechanical energy or vice versa. Depending on the detailed configuration, this can be a PTI or a PTO or both.

The drawing without small modification is without sense.

General remarks on the drawings: All figures 1, 3, 4 and 5 should be made in the same graphic style: shapes, colours, letters.

126-129 Previous: 116 Some explanation should be introduced into text.

What is calculated?: “LWL is the length of a ship or boat at the level where it sits in the water. It can be calculated by using the following relationship.”

Since when: ????

146 Carbon dioxide, it is chemical compound, should be marked as: CO₂ not as CO2, please correct it in many other places.

157 Previous 142

a) Proper marking of EF_sox should be EF_SOx taking into account the determination in row of 146.
b) In a scientific and technical article, using words to describe different values, parameters, etc. is not the best solution, even though some manuscripts do so. Please take into account the proposed symbols (acronyms) instead of words. The meaning of the symbols should be explained in the text with the units, if applicable. This approach allows you to better understand the equations and formulas. This also applies to other formulas or equations.
c) Using equation (2) it is possible to calculate the SO₂ emission, not the emission factor. Wrong equation or mistake.

165 Previous 149

What does mean: ∑MCR. I did not ask you about MCR. Explanation which was given in the cover letter about MCR is directly copied from https://www.marineinsight.com/main-engine/12-terminologies-used-for-power-of-the-ships-marine-propulsion-engine/#:~:text=Maximum%20Continuous%20Rating%20or%20MCR,of%20the%20marine%20diesel%20engine. 11 item. The authors aren't even able to add their own comments!

“g/kwh” should be: “g/kWh”.- it was not corrected

Emissions given by equation (3) is the same as given by equation (9)? It is result when the authors use full words in equations.

For all parameters used in equation (3) please give units in such way like for EF. They can be placed in the text.

171 There are two emission factors in the Table 3. One is expressed in relation to power and the other is in relation to the weight of the fuel. Both are named the same. They need to be named separately. Additionally, there is no explanation about mutual relation between them..

193 Figure 3 should be done in the same style as in Figure 1.

198 Figure 4 should be done in the same style as in Figure 1.

276 Figure 5 should be done in the same style as in Figure 1. ( It is partial copy of : Fig. 18: Illustration of operating principle during critical operations with and without battery from “Batteries on board ocean-going vessels”[10]- plagiarism!!!)

General remark: All figures 1, 3, 4 and 5 should be done in the same style. The style can be anything you like.

302 Table 7 probably should be bold

303 Table 8 probably should be bold

Unit for SFOC” (?/kWh)

306 All fonts should be the same size

307 “BP” should be italics

321 “Emission” from equation (6) is the same as “Emissions” from equation (3).

The use of such markings confuses readers and creates room for misinterpretation.

322 “BP” and “EF” should be italics

General remarks: In many places, normal and italic fonts are use for the same parameters. It is unacceptable. Dedicated symbols (acronyms) can be marked in normal font or italics, but must be the same in the text and equations. Please check it in your manuscript and correct it if necessary.

361 The drawing is copy of “Fig. 20: Principle of peak load shaving” from: “Batteries on board ocean-going vessels” [10] - plagiarism!!!)

363 Table 10. Are there any reason that “FC_Route…”are bolt?.

404 All main parameters have to be the same size of fonts. The equation uses acronyms to denote some parameters, but for other full words. I propose to use only acronyms, the meaning of which is explained in the text.

405 “BSR is the barred speed range” is not use in equation (7)

435 Table 13. Are there any reason that “L_pp” is bolt?.

422 All main parameters must be of the same size.

493 No reference.

In the equation (9) for multiplication are use different signs (‧ and ).

In the manuscript, the mathematical signs should be the same for all equations.

Comments for author File: Comments.pdf

Author Response

Comment: First of all, you only sent the "Final: Show Markup" version for review, which is correct, but with all the revision markings it is difficult to estimate the final version. Therefore, it will be very useful to get both the "Final: Show Markup" and the "Final" versions. For the next round, please send me both versions and additionally the final version of the current manuscript.

Reply: we had sent both clean (i.e. final) and track changes (i.e. show Markup) pdf files to MDPI in the previous revision. We will highlight the changes in yellow for this revision.

Comment: If the Editorial Board has given you another chance for a review, please take my comments very seriously. This is your manuscript, not mine. The manuscript should be precise and very reader-friendly, and you should realize that the manuscript is a type of presentation of the results of a research work, not a story.

Therefore, despite the many corrections that have been made, the manuscript is still not ready for printing.

The title corresponds to the content of the manuscript

Not all comments have been taken into account without sufficient explanation or discussion, so it is difficult to recommend the manuscript for printing.

Reply: We have tried our very best to reply all comments made by all reviewers. We hope that the replies are treated fairly.

99 Previous: 92

Comments: The two-stroke main engine runs on fuel. To use electricity for the propulsion system in the above very general case, it is necessary to add element(s) that convert electrical energy into mechanical energy or vice versa. Depending on the detailed configuration, this can be a PTI or a PTO or both.

The drawing without small modification is without sense.

General remarks on the drawings: All figures 1, 3, 4 and 5 should be made in the same graphic style: shapes, colours, letters.

Reply: See the updated Figure 1. During the PTO (Power Take Out) mode of operation, the shaft generator is operating as an alternator to provide the primary power supply for the vessel electrical systems. While in PTI (Power Take In) mode of operation, the shaft generator is operating as a synchronous motor. It can either provide a boost in power together with the main engine to allow the main engine to reduce power. In addition, the charge controller ensures the battery is adequately charged and not over-charged. Incorporating battery allows for peak shaving for main engine, thus reducing fuel consumption.

We also made changes to Figure 1 to have the same graphic style Figure 3 and 4. The font of the text used is Arial with size 7 italic. Note that the Figure 5 is redundant as it shows the same proposed Hybrid battery-diesel propulsion configuration. Hence, we remove Figure 5.

Comments: 126-129 Previous: 116 Some explanation should be introduced into text.

What is calculated?: “LWL is the length of a ship or boat at the level where it sits in the water. It can be calculated by using the following relationship.”

Since when: ????

Reply: Noted. We have revised the text. The hull speed can be estimated by using the following relationship in V_hull= (LWL)^0.5 * 1.34 in eqn (1). The LWL varies with the draft of the ship. In this paper, the hull speed of 14 knots is assumed.

Comments:146 Carbon dioxide, it is chemical compound, should be marked as: CO2 not as CO2, please correct it in many other places.

Reply: Noted. We have revised it to CO₂

Comments:157 Previous 142

a) Proper marking of EFsox should be EFSOx taking into account the determination in row of 146.

Reply: Noted. We have revised it to EF_SOx

Comments:b) In a scientific and technical article, using words to describe different values, parameters, etc. is not the best solution, even though some manuscripts do so. Please take into account the proposed symbols (acronyms) instead of words. The meaning of the symbols should be explained in the text with the units, if applicable. This approach allows you to better understand the equations and formulas. This also applies to other formulas or equations.

Reply: Noted. We tried to be clear on the equations used.

Comments:c) Using equation (2) it is possible to calculate the SO2 emission, not the emission factor. Wrong equation or mistake.

Reply: Noted. The emission factor of Sulphur oxide can be estimated can be estimated using equation (2).

Comment: 165 Previous 149

Reply: Noted. It is the maximum output (MW) per year that the generator is able to generate under normal condition.

Comment: “g/kwh” should be: “g/kWh”.- it was not corrected

Reply: Noted. We have revised to g/kWh.

Comment:Emissions given by equation (3) is the same as given by equation (9)? It is result when the authors use full words in equations.

Reply: Noted. We refrained from using the full words. We replace “Emissions” by “E”

Comment:For all parameters used in equation (3) please give units in such way like for EF. They can be placed in the text.

Reply: Noted. We have inserted all the units (e.g. kW, g/kWh, h) in the text for all equations.

Comment:171 There are two emission factors in the Table 3. One is expressed in relation to power and the other is in relation to the weight of the fuel. Both are named the same. They need to be named separately. Additionally, there is no explanation about mutual relation between them.

Reply: Noted. We have named the two emission factors as power based(in g/kWh) and fuel based (in g/kg_fuel). The mutual/common relation is the amount of pollutant (g) present in the emission.

	Emission factor
Pollutant	Power based	Fuel based
Pollutant	(g/kWh)	(g/)
Carbon dioxide (CO₂)	620	3179
Sulfur oxides (SO_x)	10.5	54
Nitrogen oxides (NO_x)	17	82.1

Comments:

193 Figure 3 should be done in the same style as in Figure 1.

198 Figure 4 should be done in the same style as in Figure 1.

Reply: Noted. We have revised the figures using the same styles-font size, gray/white background boxes with arrows.

Reply: Noted. Figure 5 was removed.

Comment: General remark: All figures 1, 3, 4 and 5 should be done in the same style. The style can be anything you like.

Reply: Noted. We have revised the figures using the same styles-font size, gray/white background boxes with arrows.

Comment:302 Table 7 probably should be bold

Reply: Noted. Changed to bold.

Comment:303 Table 8 probably should be bold

Reply: Noted. Changed to bold.

Comment:Unit for SFOC” (?/kWh)

Reply: Noted. It should be “g/kWh”

Comment:306 All fonts should be the same size

Reply: Noted. We have revised the font size.

Comment:307 “BP” should be italics

Reply: Noted. We have revised it.

Comment:321 “Emission” from equation (6) is the same as “Emissions” from equation (3).

Reply: Noted. We have changed the name to be different.

Comment: The use of such markings confuses readers and creates room for misinterpretation.

Reply: Noted. We had checked the paper.

Comment:322 “BP” and “EF” should be italics

Reply: Noted. We have revised both BP and EF to italics.

Comment:General remarks: In many places, normal and italic fonts are use for the same parameters. It is unacceptable. Dedicated symbols (acronyms) can be marked in normal font or italics, but must be the same in the text and equations. Please check it in your manuscript and correct it if necessary.

Reply: Noted. We ensure all parameters used in the equations are italic and they should also appear as italic in the text.

Comment:361 The drawing is copy of “Fig. 20: Principle of peak load shaving” from: “Batteries on board ocean-going vessels” [10] - plagiarism!!!)

Reply: Noted. The figure was removed.

Comment:363 Table 10. Are there any reason that “FCRoute…” are bolt?.

Reply: No. The bold was removed.

Comment:404 All main parameters have to be the same size of fonts. The equation uses acronyms to denote some parameters, but for other full words. I propose to use only acronyms, the meaning of which is explained in the text.

Reply: Noted. All acronyms are explained in the text.

Comment:405 “BSR is the barred speed range” is not use in equation (7)

Reply: BSR is the value that we want to determine in eqn (7).

Comment:435 Table 13. Are there any reason that “Lpp” is bolt?.

Reply: No. The bold was removed.

Comment:422 All main parameters must be of the same size.

Reply: Noted. All parameters are now of the same size.

Comment:493 No reference.

Reply: Noted. We inserted the reference from MAN.

Man Diesel and Turbo, MAN B&W: 6L23/30H Project guide, electronically controlled two-stroked engines, 5 Edn., MAN Diesel, Teglholmsgade 41, DK-2450 Copenhagen, Denmark, 2009.

Comment:In the equation (9) for multiplication are use different signs (‧ and ).

Reply: Noted. We have used the standard multiplication sign “´”

Comment:In the manuscript, the mathematical signs should be the same for all equations.

Reply: Noted. All mathematical symbols were standardized.

Author Response File: Author Response.pdf

Reviewer 3 Report

Please check the attached file for additional questions and comments on the paper.

Comments for author File: Comments.pdf

Author Response

Comments for Authors:

It seems that many modifications have been made in the paper. In addition, thank for your detailed answer to the question.

I would like to ask additional questions and check the contents of the paper. In the paper, the parallel hybrid system in Figure 4 is considered.

Comment: Does the ENGINES in Figure 4 mean an engine(main engine) to generate propulsion force?

Reply: Yes. It is a main engine.

Comment: And the BATTERY part in Figure 4 equal to the hybrid battery system in Figure 5?

If the battery is connected with two auxiliary engines to generate electric power, questions will arise about the purpose and usefulness of the hybrid system. In particular, the role of batteries in hybrid systems seems insignificant. If we have two auxiliary engines in hybrid system, we don t have to consider about peak saving and the fuel savings effect shown in Table 1 doesn t look so effective even if we apply peak shaving by using battery.

Reply: Sorry for the confusion. I was thinking on other system configuration while revising the paper. Figure 4 is the proposed hybrid battery system that we used in this paper. To clarify, I have removed the Figure 5 as it seems to cause confusion in this case.

Comments: The feasibility of the management cost of Eq (11) needs to be checked. It is necessary to review whether the generator may not be operated for 1,000 hours in the proposed hybrid system as shown in Figure 5 and whether it can unconditionally save maintenance costs for the generator engine under stop conditions.

Reply: Noted. The maintenance cost per year can be adjusted. Although we used 1000h, it depends on the actual operating hours of the generator which we do not have any actual or average running data on this by ship operators/owners.

Comments: Contents of 7.1 Fuel consumption and 7.2 emission are about conventional system without hybrid battery system, so it seems desirable to separate them from the 7. Applications.

Reply: Noted. We have shifted the Section 7.1 and 7.2 out from Section 7.

Comments: As I mentioned earlier, the applications and its usefulness in Ch. 7 are not accepted partially because this paper mentioned the application method and effectiveness of hybrid systems under the simple premise that hybrid propulsion systems are given. Please check this comments one more time.

Reply: Noted. We have revised the paper and check the comments again.

Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

Dear authors,

The manuscript is much better than before. I appreciate it.

Lots of things have been improved, but sorry not all of them.

Once again, please take my comments seriously. Of course, you have the right not to accept everything, but for everything it is necessary to give a logical answer, comments or explanation.

The third time I indicate there is a problem with equation (1). Please read the text that corresponds to equations (1).

It is not logical

First, you proposed to calculate the hull speed using equation (1). In the following sentences, you write the average speed is between 12 and 15 knots. And then 14 knots were applied. So where does the equation (1) come from when the experimental speed of 14 knots was used?

Text and equation are not consistent. There are some gaps in the information as to why equation (1) is represented. I asked for an explanation of the units. No answer!.

Equation (1) describes the physical parameters, so the left side of the equation and the right side must be the same unit !!!!.

Equation (3) has a similar problem. I asked the authors for units. Not all of them have been placed (load is engine load per day -unit?) But what has been done indicates that the equation shown is wrong. The units on the left are not equal to the right. This is Basic !!!! Looking at the parameters on the right side of equation (3), they are not logical.

Another equation (5), the font size on the right side is not the same as on the left side.

The parameters in Equations 5, 7, and 9 should be the same font size. Different font sizes for the same parameters may be confused with different parameters. From an editorial point of view, this is not a problem. This issue has been identified before and has not been resolved and left without comment.

Equation (6). The FC parameter was used, which in equation (5) is defined as fuel consumption per cylinder. So in equation (6) it should be multiplied by the number of cylinders.

Next. In the first revision, I indicate that the energy consumption of a seagoing vessel cannot be divided into two parts: propulsion and hotel. It's not true. In Table 15, you use data from a source that cannot be treated as a scientific article [10]. It is some specific commercial prospectus or popular science article in which the data has been simplified, which is acceptable. Such a simplification cannot be accepted in a scientific manuscript.

All new drawings should be centred.

References. Please present the quoted positions correctly and accurately in accordance with the template.

From the editorial side, please make sure that tables are not divided by two pages, chapter headings cannot be at the end of pages, and figure captions are on the same pages as the figure.

In this state of the manuscript, I do not recommend printing.

Comments for author File: Comments.pdf

Author Response

Dear authors,

Comments:

The manuscript is much better than before. I appreciate it. Lots of things have been improved, but sorry not all of them.

Once again, please take my comments seriously. Of course, you have the right not to accept everything, but for everything it is necessary to give a logical answer, comments or explanation.

Reply: Thanks for your interests in our paper. There are not many people working in these areas. We will reject the comments if we feel that the comments are illogical and personal. Some of the comments that related to formatting should be performed during typesetting stage/proof stage. For example, I do not know why the figure are not centered after using centre command in the MDPI template. We think it should be handled by the managing editor during typesetting stage as they are the expert in formatting.

Also under the same font size for the equation, the “fraction” seem to be smaller than others. We do not understand why the MDPI template create such an effect. We think it should be handled by the managing editor during typesetting stage as they are the expert in formatting.

Comments: The third time I indicate there is a problem with equation (1). Please read the text that corresponds to equations (1). It is not logical

Reply: We want to show there is such an equation that can predict the hull speed. We did not use the equation to determine the hull speed. In this paper, we simply assumed that the hull speed is 14 knots. Because, other reviewer wanted us to show how the equation look like in the previous review. I hope you can understand it is quite difficult to satisfy all reviewers simultaneously.

Comments: Text and equation are not consistent. There are some gaps in the information as to why equation (1) is represented. I asked for an explanation of the units. No answer!.

Equation (1) describes the physical parameters, so the left side of the equation and the right side must be the same unit !!!!.

Reply: This relationship was obtained from https://en.wikipedia.org/wiki/Hull_speed . We do not conduct any empirical study to obtain this relationship. We have asked my colleagues working in hydrodynamics for more than 20 years, he told me that it is a standard equation in ship design. As you mentioned in your previous comments, we can show the units in the text. Nevertheless, we just show you how the left side of the equation and the right side must be the same unit.

V_hull is the hull speed (in knots), LWL is the length of a ship at the level where it sits in the water (in feet) and the constant is given as 1.34 knots/feet^-1/2. I hope it clarify your doubt.

Comments: Equation (3) has a similar problem. I asked the authors for units. Not all of them have been placed (load is engine load per day -unit?) But what has been done indicates that the equation shown is wrong. The units on the left are not equal to the right. This is Basic !!!! Looking at the parameters on the right side of equation (3), they are not logical.

Reply: See the working on the unit below. Note that the load is the loading of the engine per day as calculated by interpolation of shop test and sea trial data (no unit).

Comments: Another equation (5), the font size on the right side is not the same as on the left side.

Reply: We had made the changes. Note that this is related to the formatting. It will be addressed during typesetting stage/manuscript proof stage.

Comments: The parameters in Equations 5, 7, and 9 should be the same font size. Different font sizes for the same parameters may be confused with different parameters. From an editorial point of view, this is not a problem. This issue has been identified before and has not been resolved and left without comment.

Reply: We had made the changes. It was due to the fraction that make the numerator and denominator small. Note that this is related to the formatting. It will be addressed during typesetting stage/manuscript proof stage.

Comments: Equation (6). The FC parameter was used, which in equation (5) is defined as fuel consumption per cylinder. So in equation (6) it should be multiplied by the number of cylinders.

Reply: Noted. We made the changes fuel consumption. It should refer to all cylinders not per cylinder.

Comments: Next. In the first revision, I indicate that the energy consumption of a seagoing vessel cannot be divided into two parts: propulsion and hotel. It's not true. In Table 15, you use data from a source that cannot be treated as a scientific article [10]. It is some specific commercial prospectus or popular science article in which the data has been simplified, which is acceptable. Such a simplification cannot be accepted in a scientific manuscript.

Reply: Noted. We think you have made a contradicting comment that confused the authors of this paper. As mentioned by you, we have the right to object to the comments. We shall do it for this comment.

Comments: All new drawings should be centred.

Reply: We had made the changes. Note that this is related to the formatting. It will be addressed during typesetting stage/manuscript proof stage.

Comments: References. Please present the quoted positions correctly and accurately in accordance with the template. From the editorial side, please make sure that tables are not divided by two pages, chapter headings cannot be at the end of pages, and figure captions are on the same pages as the figure.

Reply: We had made the changes. Note that this is related to the formatting. It will be addressed during typesetting stage/manuscript proof stage.

Comments: In this state of the manuscript, I do not recommend printing.

Reply: Noted.

Author Response File: Author Response.pdf

Reviewer 3 Report

Authors’ answers and revisions on the paper were checked.

If the feasibility of the hybrid propulsion system is presented, it is desirable to propose the specific system based on the components shown in Figure 1 and Figure 4 and to address the cost-effectiveness(including payback time) of fuel saving by applying proposed system. Modifications have not been made to this point, this paper only mentioned the application method and effectiveness of hybrid systems under the simple premise that hybrid propulsion systems are given.

However, related researchers can refer to the method of calculating fuel consumption for a designated routes, barred speed range power margin considering external forces induced by waves and wind, and the fuel saving effect of dynamo engine by incorporating battery.

Author Response

Comments: If the feasibility of the hybrid propulsion system is presented, it is desirable to propose the specific system based on the components shown in Figure 1 and Figure 4 and to address the cost-effectiveness(including payback time) of fuel saving by applying proposed system.

Reply: Thanks for your interests in our paper. We are not able to include the payback time for this paper.

Comments: Modifications have not been made to this point, this paper only mentioned the application method and effectiveness of hybrid systems under the simple premise that hybrid propulsion systems are given.

Reply: Yes. This paper only mentioned the application method and effectiveness of hybrid systems under the hybrid propulsion systems given.

Comments: However, related researchers can refer to the method of calculating fuel consumption for a designated routes, barred speed range power margin considering external forces induced by waves and wind, and the fuel saving effect of dynamo engine by incorporating battery.

Reply: Noted. However, we are not able to find a single paper that covers the entire calculation of fuel consumption for a designated routes, barred speed range power margin considering external forces induced by waves and wind, and the fuel saving effect of dynamo engine by incorporating battery.

Author Response File: Author Response.pdf

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