Analysis of long-term mechanical grooming on large-scale test panels coated with an antifouling and a fouling-release coating

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1 Biofouling The Journal of Bioadhesion and Biofilm Research ISSN: (Print) (Online) Journal homepage: Analysis of long-term mechanical grooming on large-scale test panels coated with an antifouling and a fouling-release coating John Hearin, Kelli Z. Hunsucker, Geoffrey Swain, Abraham Stephens, Harrison Gardner, Kody Lieberman & Michael Harper To cite this article: John Hearin, Kelli Z. Hunsucker, Geoffrey Swain, Abraham Stephens, Harrison Gardner, Kody Lieberman & Michael Harper (2015) Analysis of long-term mechanical grooming on large-scale test panels coated with an antifouling and a fouling-release coating, Biofouling, 31:8, , DOI: / To link to this article: View supplementary material Published online: 11 Sep Submit your article to this journal Article views: 3 View related articles View Crossmark data Full Terms & Conditions of access and use can be found at Download by: [John Hearin] Date: 14 September 2015, At: 09:28

2 Biofouling, 2015 Vol. 31, No. 8, , Analysis of long-term mechanical grooming on large-scale test panels coated with an antifouling and a fouling-release coating John Hearin*, Kelli Z. Hunsucker, Geoffrey Swain, Abraham Stephens, Harrison Gardner, Kody Lieberman and Michael Harper Center for Corrosion and Biofouling Control (CCBC), Florida Institute of Technology, Melbourne, FL, USA (Received 29 April 2015; accepted 4 August 2015) Long-term grooming tests were conducted on two large-scale test panels, one coated with a fluorosilicone fouling-release (FR) coating, and one coated with a copper based ablative antifouling (AF) coating. Mechanical grooming was performed weekly or bi-weekly using a hand operated, electrically powered, rotating brush tool. The results indicate that weekly grooming was effective at removing loose or heavy biofilm settlement from both coatings, but could not prevent the permanent establishment of low-profile tenacious biofilms. Weekly grooming was very effective at preventing macrofouling establishment on the AF coating. The effectiveness of weekly grooming at preventing macrofouling establishment on the FR coating varied seasonally. The results suggest that frequent mechanical grooming is a viable method to reduce the fouling rating of ships hulls with minimal impact to the coating. Frequent grooming could offer significant fuel savings while reducing hull cleaning frequencies and dry dock maintenance requirements. Keywords: ship hull grooming; antifouling coatings; fouling release coatings; biofouling; biofilms; macrofouling Introduction Biofouling, or the settlement and accumulation of unwanted plants and animals, is problematic in the marine environment, especially on ship hulls. Biofouling on ship hulls may lead to increases in drag, fuel consumption, emission of exhaust gases and operational costs (Swain et al. 2007; Schultz et al. 2011). The most common method of preventing fouling is through the application of antifouling (AF) coatings. These coatings may use a biocide to kill the fouling organisms, create a surface to which they find it difficult to attach (fouling-release [FR] systems) or form a hard inert surface that requires cleaning (Swain 2010). The most effective biocide-based coatings were the tributyltin (TBT) self-polishing copolymers, which were developed in the early 1970s, and were efficient at preventing growth, selfsmoothing, and had a long lifetime. Unfortunately, TBT had detrimental impacts on the environment which led to the ultimate ban for use on commercial ships in September 2008 (IMO 2001) and TBT AF paints are no longer available in most countries. These regulations created the need for replacement technologies that are as effective as TBT, but do not adversely impact the environment. Current biocidal coatings can be divided into copper-based and copper-free systems. Cuprous oxide has been used as an AF agent in paints for >200 years (WHOI 1952) and is usually combined with a co-biocide such as zinc pyrithione or 4,5-dichloro-2-octyl-4-isathiazoline-3-one to enhance its effectiveness (Finnie & Williams 2010; Muthukrishnan et al. 2014). The present shipping industry practice is to mechanically clean ship hulls when they become heavily fouled. The US Naval Ships Technical Manuals (US Navy 2006) states that when hulls have macrofouling covering >20% of the hull they must be cleaned. Cleaning cycle times vary depending on ship schedule, coating type, coating age and area of operation. This practice tends to degrade the hull coatings, release biofouling and biocides into the environment, and is being regulated and or restricted in many ports (IMO 2011). The grooming of ship hulls while in port has been proposed as a viable method to reduce the growth of biofouling on the hulls. Grooming is defined as the habitual and frequent mechanical maintenance of submerged ships hulls in order that they remain free from extraneous matter such as fouling organisms and particulate debris, with minimal impact to the coating (Tribou & Swain 2010, p. 1). Promising results from experiments that investigated the use of rotating brushes to groom small panels (Tribou & Swain 2015) has led to long-term grooming studies and the construction of a large-scale seawater test facility (LSTF) located in Port Canaveral, Florida. Grooming tests were performed for 12 months on steel test panels coated with an AF and a FR coating to determine the effectiveness of a mechanical grooming tool at reducing the growth of biofouling. *Corresponding author. jhearin@fit.edu 2015 Taylor & Francis

3 626 J. Hearin et al. Materials and methods Large-scale seawater test facility The LSTF is located in Port Canaveral, Florida, ( N, W). It is an area of high fouling activity with a mean water temperature range of 24 ± 5 C, an average salinity range of 35 ± 1.2 ppt, and water depths exceeding 4 m (NOAA 2015). The facility includes bays for static immersion testing, dynamic immersion testing, submersible vehicle testing, and grooming testing. The facility also includes a 10.4 m Mainship MK I trawler which serves as a research vessel and floating laboratory. Steel test panel assemblies The grooming tests were conducted on two steel test panel assemblies, one coated with International Intersleek 900 (International Paint LLC, Houston, TX, USA) (IS900), a fluorosilicone FR coating, and one coated with International BRA-640 (BRA640), a copper based ablative AF coating. Each coating was applied by hand as a complete system. The IS900 system consisted of two layers of epoxy basecoat, one layer of white tie coat, and one layer of blue FR topcoat. The mean topcoat dry film thickness for the IS900 coated surfaces was 181 µm. The BRA640 system consisted of two layers of epoxy basecoat, one layer of black ablative coating, and one layer of red ablative topcoat. The mean topcoat dry film thickness for the BRA640 coated surfaces was 134 µm. Each test panel assembly was 4.6 m wide and 3.4 m tall, which included a 76 cm diameter top pipe for flotation, a 4.6 m 2.4 m flat steel plate, two 15 cm diameter side braces, and a 15 cm diameter bottom brace (Figure 1). Each test panel was divided into three sections, one 5.6 m 2 grooming test section, and two 0.74 m 2 control sections. An inspection grid was applied to each grooming test section using a different color of the same top coat used on the panel. Push underwater grooming tool The push underwater grooming tool (PUG) was an electric powered, hand operated tool designed to groom ship hull coatings. The PUG consisted of four major components (Figure 2): (1) a four wheeled chassis and telescoping handle for manual control; (2) a grooming tool with five rotating brushes; (3) an impeller which provided suction to hold the PUG onto the hull; (4) an electric motor control box and battery bank power supply. (See Supplemental material Figures S1 and S2 for photographs of the PUG during deployment.) PUG chassis The PUG chassis was cut from Delrin stock material (Dupont Inc., Edge Moor, DE, USA). The chassis dimensions were 47 cm wide, 43 cm long, and 1.5 cm thick. The rear (bottom) wheels were 20 cm diameter, 4 cm wide, and mounted on a fixed axle with a treaded rubber surface. The front (upper) wheels were 7 cm diameter, 2.5 cm wide, and mounted on rotating casters with a smooth rubber surface. The telescoping handle was a 4.5 m long rod typically used for painting or window washing. PUG grooming tool The chevron shaped PUG grooming tool was 42 cm wide and 24 cm long. The gear box housing was machined from Delrin and the gears were fabricated from acetal. The five brushes were built on 7 cm diameter Delrin hubs with 0.5 cm diameter polypropylene Figure 1. Steel test panel dimensions and inspection grid configuration. Figure 2. Bottom view of the push underwater grooming tool (PUG). Rotating brushes are forward and the suction impeller is aft.

4 Biofouling 627 tufts oriented 45 from the plane of the hubs and extending 3 cm above the hubs. The grooming tool was driven by a 24 V DC Maxon motor (Maxon Precision Motors Inc., Fall River, MA, USA) (part # ) which rotated the brushes at 250 rpm while drawing 1.3 A (31 W). The motor housing and gear box was oil filled and sealed to prevent seawater intrusion. Grooming Phase 2 test Phase 2 was conducted from 17 October 2013 to 6 June Both test panels were groomed weekly using PUG. PUG was translated vertically over the test surfaces by hand at a speed of ~10 cm s 1. Two passes were made over each test section (over and back) to increase the likelihood of complete grooming coverage. PUG impeller The PUG impeller was machined from a 13 cm diameter disk of Delrin. The impeller used 12 radial vanes and a flexible rubber shroud to generate 4.5 N of suction force which could hold the PUG on any reasonably flat surface. The impeller was driven by a 48 V DC Maxon motor (part # ) which rotated the impeller at 1,200 rpm while drawing 1.6 A (77 W). The motor housing was oil filled and sealed to prevent seawater intrusion. PUG motor control box The motor control box housed the circuit boards, switches and fuses required to operate the PUG electric motors. The 24 V and 48 V DC power was supplied by a bank of four deep cycle marine batteries which were housed on the Mainship research vessel. LSTF biofouling intensity measurements Each month four clean control panels were deployed at the LSTF to measure the biofouling intensity at the test site. Each panel was 25.4 cm 30.5 cm (774.7 cm 2 ) and was coated with inert marine grade epoxy. The panels remained immersed for one month then were removed and visually assessed for biofouling intensity and organism types per ASTM D6990 (2005). The water temperature and salinity were also recorded daily at the test site to assess the water quality. Grooming test Both steel test panels were initially immersed at the LSTF on 17 August The panel coatings were allowed to condition until the grooming tests commenced on 6 September The grooming tests were conducted in three phases. Grooming Phase 1 test Phase 1 was conducted from 6 September 2013 to 11 October Both test panels were groomed weekly by hand using divers equipped with Scotch-Brite light duty cleansing pads (part # 07445). Sufficient force was applied to remove biofouling without damaging the coating. Grooming Phase 3 test Phase 3 was conducted from 6 June 2014 to 12 September The test panel coated with IS900 was groomed weekly with PUG using the same process as described above. The test panel coated with BRA640 was subdivided into two test sections. One section was groomed weekly with PUG while the other section was groomed every other week (bi-weekly) with PUG, both using the same process described above. The bi-weekly grooming regimen was adopted to determine if the favorable results from grooming the BRA640 coating weekly during Phase 2 could be duplicated with less frequent grooming. Biofouling inspection and analysis Inspection photographs The inspection grids applied to each panel divided the groomed surfaces into 35 inspection locations spread evenly over the 5.6 m 2 flat test section surfaces (Figure 1). The grid locations were spaced a minimum of 30 cm from the niche areas (corners and curved surfaces) of the panels to remove any edge effects from the inspection and analysis process. In order to capture clear and uniform inspection photographs, regardless of the seawater quality or underwater visibility, a camera water-box was designed and built. The water-box was fabricated from clear acrylic to enable the use of ambient light. The overall dimensions of the water-box were: width 25 cm, height 18 cm and length 29 cm. When in use, the water-box was filled with clean freshwater and the underwater camera with housing was mounted to one end of the box. The opposite end of the box was then placed over the desired inspection area allowing the camera to capture clear and uniform photographs with dimensions of 25 cm wide and 18 cm high (450 cm 2 ). (See Supplemental material Figure S3 for a photograph of the camera water-box.) Inspection photographs were taken at six randomly selected grid locations on each panel test section (two horizontal positions at three different depths) before and after each grooming session. Inspection photographs were also taken at six randomly selected locations on each panel control section.

5 628 J. Hearin et al. Analysis of inspection photographs Each set of six inspection photographs was visually analyzed to determine the type and percentage coverage for each biofouling organism present (ASTM D ). Visual analysis was chosen over the point intercept method as it ensured that all fouling types were identified whilst the point intercept method may miss individual organisms. The mean and standard deviation (SD) for each classification of biofouling was then calculated and plotted. Statistical analysis of inspection photographs A Mann Whitney rank sum test was performed on the inspection photograph data to compare the sample median fouling coverages between the various groomed and control surfaces. This test was chosen because the data did not follow a normal distribution. The test was used to determine whether the differences in sample medians were statistically significant within a 95% confidence interval. The results of the statistical analysis are presented by grooming test phase in Table 1. Biofilm sampling Biofilm samples were collected in situ from the groomed and ungroomed surfaces on 12 September Three samples, each covering 3.25 cm 2 of surface area, were collected from the panel test sections by divers using biofilm sampling vials designed by the Center for Corrosion and Biofouling Control (CCBC). Samples were fixed with ethanol (90/10 v/v). Ambient water samples adjacent to the panels were also collected, to determine whether using in situ seawater instead of filtered seawater would influence the results. The samples were found to contain negligible diatom cells, and thus results for ambient water samples are not presented in this manuscript. Biofilm analysis Biofilm samples were analyzed for diatom presence and abundance. Diatoms were counted and identified down to the lowest possible taxonomic level using a Nikon compound microscope equipped with 40 and 100 oil immersion objectives (Nikon Instruments Inc., Melville, NY, USA). When possible at least 300 valves of diatoms were counted and identified per sample (BSI EN ). Taxonomic identification was assisted by the references listed in Zargiel et al. (2011). Relative abundance was calculated for each sample. Coating damage and wear inspection and analysis After the completion of the 12 month grooming test, the surfaces were cleaned back by hand to remove all biofouling. Photographs were taken of the entire control surfaces and all 35 inspection grid locations on each test surface. Each photograph was analyzed visually to determine the extent of coating damage or wear. Dry film thickness measurements or microscope inspections of the coatings were not possible as other sections of these test plates were the subject of ongoing tests and could not be removed from the water. Damage to the IS900 coating was defined as removal of the blue FR top coat to reveal the white tie coat underneath. Wear on the IS900 coating was defined as any visible degradation to the blue FR topcoat. Damage to the BRA640 coating was defined as removal of both Table 1. Mann Whitney rank sum test results (α = 0.05) for comparisons of median fouling coverage between various groomed and control surfaces. Phase Coating Comparison Fouling type Statistically significant difference 1 IS900 Weekly vs control Biofilm Yes 1 IS900 Weekly vs control Macrofouling Yes 1 BRA640 Weekly vs control Biofilm Yes 1 BRA640 Weekly vs control Macrofouling Yes 2 IS900 Weekly vs control Biofilm Yes 2 IS900 Weekly vs control Macrofouling Yes 2 BRA640 Weekly vs control Biofilm Yes 2 BRA640 Weekly vs control Macrofouling Yes 3 IS900 Weekly vs control Biofilm No 3 IS900 Weekly vs control Macrofouling Yes 3 BRA640 Weekly vs control Biofilm Yes 3 BRA640 Weekly vs control Macrofouling Yes 3 BRA640 Bi-weekly vs control Biofilm Yes 3 BRA640 Bi-weekly vs control Macrofouling Yes 3 BRA640 Weekly vs bi-weekly Biofilm Yes 3 BRA640 Weekly vs bi-weekly Macrofouling Yes

6 Biofouling 629 layers of ablative coating (red and black) to reveal the epoxy base coats. Wear of the BRA640 coating was defined as erosion of the red ablative top coat to reveal the black ablative under coat. Results LSTF biofouling intensity The biofouling intensity at the LSTF showed seasonal changes in both community structure and quantity (Figure 3). This impacted the effectiveness of grooming to maintain the surfaces totally free of fouling. The fouling during Phase 1 (September to October) included biofilms, tube worms, barnacles, tunicates and encrusting bryozoans. The fouling during Phase 2 (October to June) was initially reduced in both quantity and diversity and consisted mainly of biofilms, scattered tube worms and some tunicates. After April the fouling increased and was dominated by tube worms and tunicates. The fouling during Phase 3 (June to September) included biofilms, tube worms, barnacles, tunicates and encrusting bryozoans. The seawater salinity remained fairly constant at the test site (34 35 ppt). However, the average temperature exceeded 32 C in the summer and dropped to 15 C in January. Fouling declined in the winter and was most abundant during the summer. (See Supplemental material Figure S4 for the water quality chart.) Grooming Phase 1 September 2013 to October 2013 hand groomed weekly IS900 control surfaces The biofouling on the IS900 control surfaces was limited to biofilms and tube worms (Figures 4 and 5). The biofilm coverage varied from 80% to 95% during Phase 1. The macrofouling coverage, limited to tube worms, varied from 5% to 25%. Figure 4. Phase 1 biofilm coverage with SDs for IS900 coated test panels groomed weekly by hand. Figure 5. Phase 1 macrofouling coverage with SDs for the IS900 coated test panels groomed weekly by hand. Macrofouling was limited to tube worms. IS900 groomed test surface Biofilms became established on the IS900 coating during the seven days between grooming sessions. The biofilm coverage on the pre-groomed surface varied from 50% to 75% during Phase 1 (Figures 4 and 5). The postgroomed biofilm coverage varied from 5% to 10%. The macrofouling coverage, limited to tube worms, on the pre-groomed test surface varied from 1% to 10% during that period. There was minimal macrofouling (<1%) noted on the IS900 post-groomed test surface during Phase 1. BRA640 control surfaces The biofouling on the BRA640 control surfaces was limited to biofilms and barnacles. The biofilm coverage varied from 80% to 95% during Phase 1 (Figure 6). Macrofouling coverage, limited to barnacles, on the BRA640 control surfaces varied from 2% to 10% during Phase 1 (Figure 7). Figure 3. LSTF monthly biofouling intensity and distribution during the grooming tests. BRA640 groomed test surface The biofouling on the BRA640 groomed test surface was limited to biofilms (Figures 6 and 7). The biofilm coverage

7 630 J. Hearin et al. pre-groomed or post-groomed BRA640 test surface during Phase 1. Figure 6. Phase 1 biofilm coverage with SDs for the BRA640 coated test panels groomed weekly by hand. Figure 7. Phase 1 macrofouling coverage with SDs for the BRA640 coated test panels groomed weekly by hand. Macrofouling was limited to barnacles. on the pre-groomed test surface varied from 10% to 80% during Phase 1. The post-groomed biofilm coverage was negligible (<1%). There was no macrofouling noted on the Statistical analysis of Phase 1 data The results of the Mann Whitney rank sum tests for the Phase 1 data are shown in Table 1. The results indicate that the differences in sample median fouling coverage between the weekly groomed and ungroomed control surfaces were statistically significant within a 95% confidence interval for both the IS900 and BRA640 coatings. Grooming Phase 2 October 2013 to June 2014 PUG groomed weekly IS900 control surfaces The biofouling on the IS900 control surfaces was limited to biofilms, tube worms, and encrusting bryozoans. The biofilm coverage ranged from 65% to 95% during Phase 2 (Figure 8). Macrofouling coverage on the IS900 control surfaces varied seasonally from 0% to 20% during Phase 2 (Figure 9). IS900 groomed test surface Biofilms became established on the IS900 coating during the seven days between PUG grooming sessions. The biofouling on the IS900 groomed test surface was limited to biofilms and tube worms. The biofilm coverage on the pre-groomed IS900 test surface varied from 55% to 95% during Phase 2 (Figure 8). The post-groomed biofilm coverage varied from 20% to 75%. The macrofouling coverage, limited to tube worms, on the Figure 8. Phase 2 biofilm coverage with SDs for IS900 coated test panels groomed weekly with PUG.

8 Biofouling 631 Figure 9. Phase 2 macrofouling coverage with SDs for IS900 coated test panels groomed weekly with PUG. Macrofouling was limited to tube worms and encrusting bryozoans. pre-groomed test surface varied seasonally from 0% to 3% (Figure 9). There was minimal macrofouling (<1%) noted on the post-groomed IS900 test surface during Phase 2. BRA640 control surfaces The biofouling on the BRA640 control surfaces was limited to biofilms and barnacles. The biofilm coverage varied from 70% to 90% during Phase 2 (Figure 10). Macrofouling coverage, limited to barnacles, on the BRA640 control surfaces gradually increased from 10% to 30% between 17 October and 15 November, when the control surfaces were cleaned back (Figure 11). Macrofouling coverage on the control surfaces remained minimal during the cooler months then gradually increased to 15% by June BRA640 groomed test surface The biofouling on the BRA640 groomed test surface was limited to biofilms (Figures 10 and 11). The biofilm coverage on the pre-groomed BRA640 test surface varied seasonally from 10% to 90% during Phase 2. The post-groomed biofilm coverage varied from 0% to 10% during the initial period from October 2013 to January Figure 10. Phase 2 biofilm coverage with standard deviations for BRA640 coated test panel groomed weekly with PUG.

9 632 J. Hearin et al. Figure 11. Phase 2 macrofouling coverage with SDs for BRA640 coated test panels groomed weekly with PUG. Macrofouling was limited to barnacles The post-groomed biofilm coverage gradually increased from 10% to 80% during the period from January to June There was no macrofouling coverage noted on the pre-groomed or post-groomed BRA640 test surface during Phase 2. Statistical analysis of Phase 2 data sets The results of the Mann Whitney rank sum tests for the Phase 2 data are shown in Table 1. The results indicate that the differences in sample median fouling coverage between the weekly groomed and ungroomed control surfaces were statistically significant within a 95% confidence interval for both the IS900 and BRA640 coatings. Grooming Phase 3 June 2014 to September 2014 PUG groomed weekly or bi-weekly IS900 control surfaces The biofouling on the IS900 control surfaces consisted of biofilms, tube worms, encrusting bryozoans, and tunicates (Figures 12 and 13). The biofilm coverage on the IS900 control surfaces varied from 50% to 80% during Phase 3. Macrofouling coverage on the IS900 control surfaces gradually increased from 0% (post cleaning on June 12) to 35% by the end of Phase 3. Macrofouling coverage on the post-groomed test surface, consisting of tube worms and encrusting bryozoans, varied from 2% to 25% during Phase 3. BRA640 control surfaces The biofouling on the BRA640 control surfaces was limited to biofilms and barnacles (Figures 14 and 15). The biofilm coverage on the BRA640 control surfaces increased from 40%, one week after cleaning on 12 June, to 80% coverage four weeks later. The control surfaces were cleaned back again on 8 August. Biofilm coverage then varied from 10% to 80% during the remainder of Phase 3 (Figure 14). Macrofouling coverage on the BRA640 control surfaces, limited to barnacles, increased from 5%, one week after cleaning on 12 June, to 30% seven weeks later. After cleaning on 8 August, macrofouling coverage increased from 2% to 45% after five weeks (Figure 15). IS900 test surface groomed weekly The entire IS900 test surface was groomed weekly with PUG during Phase 3. The biofouling on the IS900 groomed test surface was limited to biofilm, tube worms, and encrusting bryozoans (Figures 12 and 13). The postgroomed biofilm coverage varied from 40% to 75%. Figure 12. Phase 3 biofilm coverage with SDs for IS900 coated test panels groomed weekly with PUG.

10 Biofouling 633 Figure 13. Phase 3 macrofouling coverage with SDs for IS900 coated test panels groomed weekly with PUG. Macrofouling on the groomed surfaces was limited to tube worms and encrusting bryozoans. Macrofouling on the control surfaces consisted of tube worms, encrusting bryozoans, and tunicates. Figure 15. Phase 3 macrofouling coverage with SDs for BRA640 coated test panels groomed weekly or bi-weekly with PUG. The control surfaces were cleaned back on 12 June and 8 August, which explains the lower biofilm fouling cover during the inspections immediately thereafter. BRA640 test surface - groomed weekly The biofouling on the weekly groomed BRA640 test surface was limited to biofilm (Figures 14 and 15). The weekly groomed biofilm coverage varied from 65% to 80% during Phase 3. No macrofouling coverage was noted on the weekly groomed BRA640 test surface. BRA640 test surface groomed bi-weekly The biofouling on the bi-weekly groomed BRA640 test surface was limited to biofilm and barnacles (Figures 14 and 15). The bi-weekly groomed biofilm coverage varied from 80% to 90% during Phase 3. The macrofouling coverage on the bi-weekly groomed BRA640 test surface, limited to barnacles, increased from 0% to 5% by the end of Phase 3. Statistical analysis of Phase 3 data sets The results of the Mann Whitney rank sum tests for the Phase 3 data are shown in Table 1. The results indicate that the differences in sample median fouling coverage between the IS900 weekly groomed and ungroomed control surfaces were statistically significant within a 95% confidence interval for macrofouling but were not significant for biofilm. This was due to the development and persistence of tenacious biofilms on the IS900 coating. The results also indicate that the differences in sample median fouling coverage between the BRA640 weekly groomed, bi-weekly groomed, and ungroomed control surfaces were statistically significant within a 95% confidence interval for all comparisons. Biofilm analysis At the end of the 12 month grooming test, the surfaces were sampled to identify the relative abundance of diatom populations that were present. A total of 51 diatom species were identified on the two coatings, 39 pennate and 12 centric. Observations are presented based on diatom community composition for coating type (IS900 vs BRA 640). (See Supplemental material Figures S5 and S6 for the biofilm analysis charts.) Figure 14. Phase 3 biofilm coverage with SDs for BRA640 coated test panels groomed weekly or bi-weekly with PUG. Macrofouling was limited to barnacles. The control surfaces were cleaned back on 12 June and 8 August, which explains the lower biofilm fouling cover during the inspections immediately thereafter. IS900 test surface groomed weekly The control and pre-groom surfaces were similar in community composition and were dominated by the diatom genera Achnanthes, Navicula, Nitzschia and Skeletonema. Post-groomed samples had less diatom diversity (based on the number of diatom species present) as well as a shift in diatom dominance. Post-groomed biofilms were dominated by species of Achnanthes, Amphora and Navicula.

11 634 J. Hearin et al. BRA640 test surface groomed weekly On the weekly groomed BRA640 surface, the pregroomed samples were dominated by species of Amphora, Navicula and several centric diatoms including species of Chaetoceros, Leptocylindris and Odontella (Figure 13). The post-groomed biofilms were dominated by Amphora. BRA640 test surface groomed bi-weekly On the bi-weekly groomed BRA640 surface, the pre-groomed samples were dominated by the pennate diatom genus Amphora and the centric diatom genus Skeletonema, with the addition of several species of pinnate diatoms, which in this case were species of Fragilaria and Plagiotropis. The post-groomed surfaces were almost 100% dominated by Amphora spp. Coating damage and wear analysis IS900 coating wear The results of the IS900 coating wear analysis are summarized in Table 2. No degradation of the blue fouling release top coat was noted in the photographic visual inspections for either the groomed or control surfaces. BRA640 coating wear The results of the BRA640 coating wear analysis are summarized in Table 2. The mean erosion of the red ablative topcoat for the groomed test surface was 12%. The mean erosion of the red ablative topcoat for the control surface was 31%. The black ablative undercoat of BRA640 showed no signs of wear on either surface. The results of the Mann Whitney rank sum test confirmed that the differences in sample median coating wear between the groomed and control surfaces were statistically significant within a 95% confidence interval for the BRA640 coating. IS900 coating damage The results of the IS900 coating damage analysis are summarized in Table 3. The mean damage of the FR topcoat for the groomed test surface was 3%. The majority of the groomed topcoat damage occurred around the weld bead located in the center of the test panel and appears to have been caused by plate handling, coating delamination, and fish bites rather than from the grooming tool. The mean damage of the FR topcoat for the control surface was 5%. The results of the Mann Whitney rank sum test confirmed that the differences in sample median coating damage between the groomed and control surfaces were statistically significant within a 95% confidence interval for the IS900 coating. BRA640 coating damage The results of the BRA640 coating damage analysis are summarized in Table 3. No damage to the two layers of ablative coating was noted in the photographic visual inspections for either the groomed or control surfaces. Discussion Grooming Phase 1 hand groomed weekly Weekly hand grooming was effective at removing most biofilm growth from the IS900 coated test surface. Some tenacious forms of biofilm remained on the test surface at area coverages of <10%. These tenacious biofilms were very low profile, <1 mm thick, and tended to form in the orange peel indentations in the coating. Macrofouling decreased with time on the IS900 control surfaces due to decreasing water temperatures and fish predation. Weekly hand grooming was very effective at removing virtually all biofilm growth from the BRA640 test surface. Weekly hand grooming also prevented the establishment of any macrofouling on the BRA640 coated test surface. The results indicated that weekly hand grooming could significantly reduce biofilm coverage on submerged surfaces coated with IS900 or BRA640, and could prevent the establishment of macrofouling. The weekly hand grooming results were within expectations since divers could visually verify total grooming coverage and apply sufficient effort to remove all but the most tenacious biofilms from both test surfaces. The hand Table 2. Test panel coating wear. Coating BRA640 BRA640 IS900 IS900 Test panel surface Control Groomed Control Groomed Topcoat maximum wear (%) Topcoat minimum wear (%) Topcoat mean wear (%) SD (%) The BRA640 coating values represent the percentage of the red topcoat ablative layer which had eroded to reveal the black ablative undercoat layer. The IS900 coating values represent the percentage of visible degradation noted on the blue topcoat.

12 Biofouling 635 Table 3. Test panel coating damage. Coating BRA640 BRA640 IS900 IS900 Test panel surface Control Groomed Control Groomed Maximum coating damage (%) Minimum coating damage (%) Mean damage (%) SD (%) Values represent the percentage of topcoat layers which had been removed to reveal the tie coat or epoxy base coats by the end of the grooming test. grooming results were adopted as the baseline for comparison with mechanical grooming. Grooming Phase 2 PUG groomed weekly Weekly mechanical grooming with PUG was effective at removing loose and/or heavy biofilm settlement from the IS900 coated test surface but could not remove the tenacious forms of low-profile biofilm described above (Figure 8). Some encrusting bryozoans (2% coverage) became established on the groomed test surface by the end of Phase 2 when the macrofouling intensity began to increase. Weekly mechanical grooming with PUG was initially very effective at removing biofilm growth from the BRA640 coated test surface. Low-profile tenacious forms of biofilm began to appear during the winter months and were well established by the end of Phase 2 (Figure 10). Weekly mechanical grooming with PUG prevented the establishment of any macrofouling on the BRA640 coated test surface during Phase 2. Overall, the results indicated that weekly mechanical grooming with PUG could significantly reduce loose and/or heavy biofilm coverage on submerged surfaces coated with IS900 or BRA640, and could significantly reduce or prevent the establishment of macrofouling. These results compare favorably with the hand grooming results from Phase 1. These results also agreed favorably with the results from Tribou and Swain (2015), where weekly mechanical grooming was able to remove loose biofilms and most macrofouling from both IS900 and BRA640 coatings. The results also demonstrated that weekly mechanical grooming with PUG could not prevent the establishment of low-profile tenacious biofilms on submerged surfaces coated with IS900 or BRA640. Tenacious biofilms were not noted in the results from Tribou and Swain (2015). The most likely explanation for this difference is that the test site used by Tribou and Swain (2015) was much closer to the open ocean and had more stable salinity and less turbidity than the LSTF site. Also, the much smaller test panels used by Tribou and Swain (2015) were only exposed for three months of weekly grooming and therefore did not encounter the same level of exposure or fouling intensity as the large-scale panels used at the LSTF. Most of the low-profile tenacious biofilms noted on both coatings during Phase 2 could be easily removed with a bare hand, which suggested that a more effective grooming tool may be able to better control the establishment of these tenacious biofilms. Grooming Phase 3 PUG groomed weekly or biweekly Weekly mechanical grooming with PUG was effective at removing loose and/or heavy biofilm settlement from the IS900 test surface but could not remove the tenacious forms of low-profile biofilm (Figure 12). Macrofouling, limited to tube worms and encrusting bryozoans, was able to become established on the groomed surfaces during the high fouling season (June to October) of Phase 3 and could not be removed by PUG (Figure 13). This was most likely due to the abundance of macrofouling organisms at this time of year and their rate of growth. It may also be possible that aging or microscopic coating wear had reduced the performance of the coating. Weekly mechanical grooming with PUG was effective at removing loose and/or heavy biofilm settlement from the BRA640 test surface but could not remove the tenacious forms of low-profile biofilm (Figure 14). Weekly mechanical grooming with PUG was effective at preventing the establishment of macrofouling on the BRA640 coating during Phase 3 (Figure 15). Bi-weekly mechanical grooming with PUG was effective at removing loose and/or heavy biofilm settlement from the BRA640 test surface but could not remove the tenacious forms of low-profile biofilm (Figure 14). Additionally, a small percentage of macrofouling, limited to barnacles, was noted on the bi-weekly groomed test surface during Phase 3 (Figure 15). Overall, the results indicate that weekly mechanical grooming with PUG could significantly reduce loose and/or heavy biofilm coverage on submerged surfaces coated with IS900 or BRA640. Weekly mechanical grooming with PUG was more effective at reducing biofilm growth on the BRA640 coated test surface than bi-weekly grooming, and weekly grooming was able to prevent the establishment of macrofouling on BRA640

13 636 J. Hearin et al. while bi-weekly grooming was less successful at preventing macrofouling. The results for the BRA640 coating compare favorably with the results of Tribou and Swain (2015), where weekly mechanical grooming was able to remove loose biofilms and macrofouling while bi-weekly grooming was less successful. The results for the IS900 coating did not compare well with the results of Tribou and Swain (2015), where weekly mechanical grooming was able to prevent the establishment of loose biofilms and macrofouling. Tenacious biofilms were not noted in the results from Tribou and Swain (2015). The most likely explanation for this difference is that the test site used by Tribou and Swain (2015) was much closer to the open ocean and had more stable salinity and less turbidity than the LSTF site. Also, the much smaller test panels used by Tribou and Swain (2015) were only exposed for three months of weekly grooming and therefore did not encounter the same level of exposure or fouling intensity as the large-scale panels used at the LSTF. Most of the low-profile tenacious biofilms noted on both coatings during Phase 3 could be easily removed with a bare hand which suggested that a more effective grooming tool may be able to better control the establishment of these tenacious biofilms. Impact of low-profile tenacious biofilm on skin friction drag The impact of very low-profile tenacious biofilms (< 1 mm thick) on the overall skin friction drag on ship hulls coated with AF or FR coatings is not easily quantified (Schultz & Swain 2000; Townsin 2003). Previous predictions for the total resistance increase due to light slime on AF coatings range from 7% to 10% (Schultz 2007; Schultz et al. 2011). It is not clear what impact the very low-profile tenacious biofilms noted during this grooming test would have on skin friction drag. Research is currently underway at the CCBC to better quantify the impacts of these very low-profile tenacious biofilms on ship hull skin friction drag. Biofilm analysis The diatom community composition was different between the two coating surfaces (IS900 vs BRA640). There was a greater richness of diatom species present on the IS900 compared to the BRA640; this was apparent for both the pre- and post-groomed samples. These results correspond to previous studies which have found greater diversity present on FR surfaces compared to AF surfaces (Molino et al. 2009; Zargiel et al. 2011; Zargiel & Swain 2014; Van Mooy et al. 2014), as not all diatom genera have the morphology or physiological adaptations that allow them to resist exposure to copper or other toxins. Grooming of both IS900 and BRA640 changed the diatom community composition. On both of these surfaces, grooming significantly decreased the abundance of centric diatoms present within the biofilm. Usually centric diatoms are found in low numbers within the biofilm community (Zargiel et al. 2011), suggesting their presence is due to chance entrainment. However, the biofilms on the BRA640 test surfaces had centric diatoms that were both present and abundant within the biofilm, especially Skeletonema costatum. It is possible that the biofilms had been cultivated as part of a long-term grooming experiment, creating a thicker biofilm than normally present on static exposed panels, allowing for easier attachment of the cells to the biofilm. The overall thickness of the biofilms as a result of grooming, and its impact on the subsequent biofilm community, will need to be investigated further. Grooming also selected for a community that was predominantly dominated by the genera Amphora and Navicula. Both are raphid diatoms, which secrete EPS to facilitate attachment to a surface. These genera have been reported attached to ship hull coatings exposed to dynamic conditions (Zargiel & Swain 2014) as well as on in-service ship hulls (Hunsucker et al. 2014), so their persistence and consequent dominance on a groomed (disturbed) surface is not surprising. In general, grooming selected for pennate diatoms and removed those diatom species (especially centrics) which have been shown to have low adhesion to ship hull coatings (Zargiel & Swain 2014; Hunsucker & Swain 2015). Coating damage and wear The results of the coating wear analysis suggest that weekly mechanical grooming with PUG imparted no visible wear on the IS900 coated test surface (Table 2). These results agree well with the results of Tribou and Swain (2015), where microscope inspections found no physical wear on the IS900 coating after six months of weekly and bi-weekly mechanical grooming. Since microscope inspections could not be performed on the large-scale test panels after the grooming tests, it may be possible that microscopic wear was present but not detectable. The damage analysis results suggest that the force required to clean back the heavily fouled IS900 control surfaces caused more topcoat damage than mechanical grooming caused during a year of weekly grooming. The majority of the groomed topcoat damage occurred around the weld bead located in the center of the test panel and appears to have been caused more by plate handling, coating delamination, and fish bites than from grooming. These results agree well with the results of

14 Tribou and Swain (2015), where microscope inspections noted minimal damage to the IS900 topcoat after six - months of weekly and bi-weekly mechanical grooming. The BRA640 coating is designed to be ablative and some topcoat erosion was expected. However, it appears that the groomed surfaces had reduced erosion compared to the control surfaces. The wear analysis results suggest that the force required to clean back the heavily fouled BRA640 control surfaces caused more topcoat wear than mechanical grooming caused during a year of weekly or bi-weekly grooming. These results agree well with the results of Tribou and Swain (2015), where microscope inspections noted some erosion of the BRA640 ablative topcoat after six months of weekly and bi-weekly mechanical grooming. No damage to the two layers of BRA640 ablative coating was noted in the photographic visual inspections for either the groomed or control surfaces. Again, these results agree well with the results of Tribou and Swain (2015), where microscope inspections noted no damage to the BRA640 topcoat after six months of weekly and bi-weekly mechanical grooming. Conclusions The results from this research have demonstrated that weekly mechanical grooming with a rotating brush tool similar to those used on PUG could provide a viable method to reduce the fouling rating of ship hulls coated with IS900 FR or BRA640 AF coatings while imparting minimal impact to the coatings while the ships are in port or at anchor. Weekly mechanical grooming was shown to be very effective at preventing the establishment of macrofouling on surfaces coated with BRA640. The effectiveness of weekly grooming at preventing macrofouling settlement on IS900 may be more seasonally dependent or may require a more effective grooming tool. The reduction in the fouling rating of ship hulls by frequent grooming could offer significant reductions in drag, fuel consumption, and the emission of exhaust gases (Swain et al. 2007; Schultz et al. 2011). Frequent grooming could also eliminate the need for hull cleaning and increase the time between dry docking which would reduce the operational costs for many vessel operators. Acknowledgements The authors would like to thank the members of the Center for Corrosion and Biofouling Control for their help in the field and laboratory. Disclosure statement No potential conflict of interest was reported by the authors. Funding Biofouling 637 This work was funded by the Office of Naval Research [grant N ]. Supplemental material The supplemental material for this paper is available online at References ASTM D Standard practice for evaluating biofouling resistance and physical performance of marine coating systems. West Conshohocken, PA: ASTM International. BSI EN Water quality guidance for the identification, enumeration, and interpretation of benthic diatom samples from running waters. BSI, EN Finnie AA, Williams DN Paint and coatings technology for the control of marine fouling. In: Dürr S, Thomason JC, editors. Biofouling. Oxford: Wiley-Blackwell; p Hunsucker KZ, Koka A, Lund G, Swain G Diatom community structure on in-service cruise ship hulls. Biofouling. 30: Hunsucker KZ, Swain GW In situ measurements of diatom adhesion to silicone ship hull coatings. J Appl Phycol. 0584:3 9. doi: /s IMO Guidelines for the control and management of ships biofouling to minimize the transfer of invasive aquatic species. Resolution MEPC. 207, annex 26. IMO International convention on the control of harmful antifouling systems on ships. London: IMO. Molino PJ, Childs S, Eason-Hubbard MA, Carey JM, Burgman MA, Wetherbee R Development of the primary diatom microfouling layer on antifouling and fouling release coatings in temperate and tropical environments in Eastern Australia. Biofouling. 25: Muthukrishnan T, Abed RM, Dobretsov S, Kidd B, Finnie AA Long-term microfouling on commercial biocidal fouling control coatings. Biofouling. 30: NOAA National Data Buoy Center. Retrieved from Station TRDF Trident Pier: noaa.gov/station_page.php?station=trdf1 Schultz MP Effects of coating roughness and biofouling on ship resistance and powering. Biofouling. 23: Schultz MP, Bendick JA, Holm ER, Hertel WM Economic impact of biofouling on a naval surface ship. Biofouling. 27: Schultz MP, Swain GW The influence of biofilms on skin friction drag. Biofouling. 15: Swain G The importance of ship hull coatings and maintenance as drivers for environmental sustainability proceedings ship design operation environmental sustainability. London: RINA. Swain G, Kovach B, Touzot A, Casse F, Kavanagh CJ Measuring the performance of today s antifouling coatings. Journal of Ship Production. 23: Townsin RL The ship hull fouling penalty. Biofouling. 19:9 15. Tribou M, Swain G The use of proactive in-water grooming to improve the performance of ship hull antifouling coatings. Biofouling. 26:47 56.

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