The Use of Tunable Encapsulation for Long-Term Fouling Control

Round 1

Reviewer 1 Report

This is quite innovative, original and efficient research in the control of biofouling in the applied study area. It has an appropriate experimental design and very well described and illustrated methodology. The statistical analysis of the data obtained is relevant to the type of study. The results are clearly presented and easy to interpret. The Discussion and its conclusions are strongly supported by the results obtained. It is suggested to incorporate more updated bibliography.

Author Response

Thank you for the review. We appreciate your time. We have added additional, recent publications to enhance the reference list. 

Reviewer 2 Report

The article investigates a new novel semipermeable encapsulation technology to solve the surface fouling problem with a long experimental period, proves the reliability of this technology through a large amount of experimental data and analyzes its working mechanism. The research content is somewhat innovative, and it is suggested to be modified from the following aspects:

1. The meaning of "stderr" in table 1 is not reflected in the text, and the author is requested to elaborate on it;

2. The legend in Figure 4a is not clearly expressed and it is difficult to distinguish the difference between different types of sleeves. In addition, the time expressions of the horizontal coordinates (A-17 to O-18) are not consistent with those of Figure B. Please standardize the time expressions and explain them in the text;

3. In Figure 5, the interval from A-17 to O-18 is 18 months, and the text mentions that the immersion period is 20 months, so please ask the authors to explain it or complete the experimental data;

4. There are mutations in the O-17 data in Figure 5, please explain them;

5. Line 207 refers to " In contrast, the controls did not significantly vary between months.", which is not reflected in Figures 7 and 8;

6. Line 263 refers to "pH only varied significantly in three months", which is not reflected in Figure 9d;

7. References have been low in recent years.

8. The abstract needs to be supplemented and improved.

Author Response

Thank you for reviewing our manuscript. Your comments led to our catching an error in the figures and have improved things greatly. Below are specific corrections made in response to your comments:

1. The meaning of "stderr" in table 1 is not reflected in the text, and the author is requested to elaborate on it;
   1. This was addressed in lines 164-174 (161-162 in clean copy). Stderr was clarified as the standard error, and the equation used for the calculation was inserted.

2. The legend in Figure 4a is not clearly expressed and it is difficult to distinguish the difference between different types of sleeves. In addition, the time expressions of the horizontal coordinates (A-17 to O-18) are not consistent with those of Figure B. Please standardize the time expressions and explain them in the text;
   1. Line color and style were changed to make the image clearer. Labels on the x-axis were standardized to match Figure B.

3. In Figure 5, the interval from A-17 to O-18 is 18 months, and the text mentions that the immersion period is 20 months, so please ask the authors to explain it or complete the experimental data;
   1. Axis label was updated to make the time clearer. Additionally, the timetable for data collection was clarified in the caption.
4. There are mutations in the O-17 data in Figure 5, please explain them;
   1. Thank you, we rechecked the data and corrected the graphs. 

5. Line 207 refers to " In contrast, the controls did not significantly vary between months.", which is not reflected in Figures 7 and 8;
   1. The language in line 226-227 was corrected to reflect that the difference between the controls was based on the length of time the controls had been immersed. 

6. Line 263 refers to "pH only varied significantly in three months", which is not reflected in Figure 9d;
   1. Colors and line styles were changed to make the variation on the graph more visible. Additionally, the scale of the y-axis was changed to represent the scale of the data better.  
7. References have been low in recent years.
   1. Additional references have been added from more recent publications. 
8. The abstract needs to be supplemented and improved.
   1. More information has been added to the abstract. It has been expanded and clarified. 

 

Reviewer 3 Report

The paper presents interesting results however can be accepted for publication only after major revision. Some issues should be clarified.

The primary focus of this study is antifouling systems, with a particular emphasis on biocides. Surprisingly, the authors have not delved into this crucial topic beyond a brief mention that the biocides used are copper-free and selected for their eco-friendliness. To enhance the paper, it is imperative to provide comprehensive information on the biocides, including their specific type, manufacturer, advantages, and disadvantages. Furthermore, an in-depth discussion is warranted on the mechanisms underlying the antifouling properties, the concentration levels of the biocides employed, and their safety implications for both humans and marine organisms.

The authors mention, "There was no macrofouling...," suggesting that microscopic observations of the polyester fabrics were not carried out. However, such microscopic observations are vital to understanding the dynamics of fouling in this context and should not be omitted.

Additionally, the paper lacks a comparison with prior studies that have described similar non-fouling systems (e.g., references: https://doi.org/10.1128/AEM.65.4.1603-1609.1999 and https://doi.org/10.1039/C9RA10874B). It is essential to include a detailed discussion of the advantages and disadvantages of the proposed technology in relation to previous works to provide a more comprehensive view of the research landscape.

Minor editing of English language required.

Author Response

Thank you for reviewing our manuscript. I fear there may have been some misunderstanding on the focus and design of our novel antifouling. The encapsulation referred to in this manuscript is covering, enclosing, wrapping or sheathing the surface that we are protecting in a sleeve, bag or cover that prevents biofouling. The fabric cover does have a coating that contains biocide(s), however, this is not the primary focus, nor is it the only protective mechanism. The coated fabric encapsulation (or wrap, if you prefer) is proprietary and provided for testing by Biofouling Technologies, Inc. We cannot divulge the information on the biocides. Again, the biocides are only a small part of the antifouling impact of the holistic fabric enclosures. Please refer to Figure 1 to see that we enclosed a bronze panel (propeller mimic) in a coated, fabric sleeve. There is a gap between the sleeve and the panel (mentioned in the method) so that the panels are never in contact with the biocide.

We did not look at the fabrics under a microscope. In fact, we only report on the fouling on the bronze. There was visible fouling on the wrap, both micro- and macrofouling, but it was not the focus of the experiment so we didn’t report on it.

We have added additional references to increase the number of recent citations. The Hopkins et al and Floerl et al papers specifically refer to encapsulation as we have used the term.  

Reviewer 4 Report

The paper outlines a series of field experiments to determine the efficacy of a modified encapsulation method to control the fouling of propellers (the authors cite other niche areas in the introduction, although it is unclear how widely applicable this method would be).

The work is technically sound and quite interesting - although note the point about controls below.  There are the usual issues common among industry-funded projects, of little (in this case zero) information being provided about the biocides being tested.  It is for the editor to decide whether this should prevent publication.  I presume the authors would argue that the nature of the fabric, rather than the biocide, is the factor under investigation.

Some minor comments:

Line 16 (and throughout) - For the avoidance of doubt, the authors should use the term ‘biofouling’ rather than ‘fouling’ to describe active settlement/adhesion/accumulation of living things, as opposed to deposition of non-living material.

Line 56 - The first few lines of the methods are confusing.  They describe the production of fabric sleeves but then immediately shift to discussing a proprietary antifouling coating.  At this point in the paper it is unclear if this coating on the sleeves, or on the substrate inside the sleeves, or somewhere else.  Please provide more detail, even very general, about the manufacturing process of the fabric.

Line 59, 61 - It would help readers outside the US if metric units were used (as on line 66), with imperial measurements in brackets if necessary, as done later for pressure.  A yard is pretty abstract to most people.

Line 281 - I think it would be useful to include (in supplementary materials) the previous unpublished data for uncoated fabric.  One of the things I struggled with in this paper was the lack of context for how a ‘control fabric’ would perform, as opposed to an unencapsulated metal surface (which is not really a control for the experiment).  If we are being picky, the work as presented contains no real control, since for all we know an uncoated fabric could screen out all biofouling entirely with the unspecified biocide having no effect.  It is also only really at this stage in the paper that there is any discussion of the material’s coating.  You can’t say much, if it’s proprietary, but I think it needs to be explicit, earlier, that the fabric is biocide-coated and roughly how this was achieved.

Line 299 - Define ‘long term’ in the context of this study.

Is the pore-area to fabric-area ratio of relevance?  I.e the thickness of the material fibres in relation to the pores?  Presumably too thick and these would provide a settlement substrate and foul themselves?

Is there a reason that the bags are porous and not made hermetic? I don’t think this is addressed anywhere and seems to be an obvious point.

Generally fine, but the sentence structure can be a little strange throughout.  Worth a proof-read.

Author Response

Thank you for the detailed review. We have addressed your concerns throughout the manuscript. Detailed responses are below:

The work is technically sound and quite interesting - although note the point about controls below.  There are the usual issues common among industry-funded projects, of little (in this case zero) information being provided about the biocides being tested.  It is for the editor to decide whether this should prevent publication.  I presume the authors would argue that the nature of the fabric, rather than the biocide, is the factor under investigation.

• Yes, it is the nature of the fabric and not the biocide. We have tested other coatings and application systems in previous experiments (and other fabrics etc) and had similar or lesser success. While we agree that keeping the identities of the biocides proprietary seems overly protective, it is outside of our control. The presence of biocide is important but the identity of the biocide is not critical to the performance of the technology.

Some minor comments:

Line 16 (and throughout) - For the avoidance of doubt, the authors should use the term ‘biofouling’ rather than ‘fouling’ to describe active settlement/adhesion/accumulation of living things, as opposed to deposition of non-living material.

- Changed the first reference on line 16 and in the abstract. However, we only talk about biofouling when we reference fouling and clearly differentiate between that and non-biological chalks. Clarified this in Line 16 in the text

Line 56 - The first few lines of the methods are confusing.  They describe the production of fabric sleeves but then immediately shift to discussing a proprietary antifouling coating.  At this point in the paper it is unclear if this coating on the sleeves, or on the substrate inside the sleeves, or somewhere else.  Please provide more detail, even very general, about the manufacturing process of the fabric.

- Clarified: Sleeves of three coated polyester fabrics, 40 TXT, 50 TXT and Spun, were fabricated (Figure 1). The sleeves consisted of a fabric that had been coated with a proprietary antifouling coating that was designed to ablate during immersion.

Line 59, 61 - It would help readers outside the US if metric units were used (as on line 66), with imperial measurements in brackets if necessary, as done later for pressure.  A yard is pretty abstract to most people.

- Apologies, we are working with an American company and these were developed to allow us to compare many different combinations of fabric/coating. We didn’t even think to correct units to metric. It has been done.

Line 281 - I think it would be useful to include (in supplementary materials) the previous unpublished data for uncoated fabric.  One of the things I struggled with in this paper was the lack of context for how a ‘control fabric’ would perform, as opposed to an unencapsulated metal surface (which is not really a control for the experiment).  If we are being picky, the work as presented contains no real control, since for all we know an uncoated fabric could screen out all biofouling entirely with the unspecified biocide having no effect.  It is also only really at this stage in the paper that there is any discussion of the material’s coating.  You can’t say much, if it’s proprietary, but I think it needs to be explicit, earlier, that the fabric is biocide-coated and roughly how this was achieved.

- I have added to the methods an explicit statement that the fabric is coated. The process is part of what makes it proprietary. The company has developed a method of applying the coating (also proprietary and made in house). I shudder when I think of the uncoated fabric, because it was a nightmare to deal with after it had been exposed for a short period of time (1-2 months) and became funky and slippery with fouling. It was not sustainable, after seeing the ineffectiveness of the uncoated fabric, to include these with every experiment. I’ve added a couple of graphs to an appendix showing the fouling performance and dissolved oxygen of the uncoated fabric.

Line 299 - Define ‘long term’ in the context of this study.

- Defined

Is the pore-area to fabric-area ratio of relevance?  I.e the thickness of the material fibres in relation to the pores?  Presumably too thick and these would provide a settlement substrate and foul themselves?

- Because of the variability of the pores, especially spun with the fibrous texture, no calculation of this type could be done. I’m not sure what you are asking here.

Is there a reason that the bags are porous and not made hermetic? I don’t think this is addressed anywhere and seems to be an obvious point.

- Anoxic conditions can lead to negative effects with the materials, especially over longer time periods. Mostly the fully sealed wraps are only used for a week or maybe a month at most. Additionally, if something damages the encapsulation, the protection is lost wherever fresh water intrudes. This is discussed starting around line 270.

Round 2

Reviewer 2 Report

3. There are mutations in the O-17 data in Figure 5, please explain them;
   1. Thank you, we rechecked the data and corrected the graphs.

I noticed that the mutations in the revised manuscript has disappeared. Why has the mutations disappeared.

Author Response

In response to your comment, we went and looked back at the data and realized we had made an error when we generated the graphs. It passed through our editing because we assumed that was the hurricane evacuation. However, we realized we just had a copy - paste error when we dug a little deeper. We fixed the data error and inserted the updated graphs. Again, thank you for catching this and causing us to look again. 

Reviewer 3 Report

After a detailed explanation by the authors, I believe that the paper can be accepted in its present form

Minor editing of English language required.

Author Response

Thanks for your re-review. We appreciate your time and effort on this.