AN UPDATE ON MARINE ANTIFOULINGS

Transcription

1 25 th ITTC Group Discussions 3 Global Warming and Impact on ITTC Activities AN UPDATE ON MARINE ANTIFOULINGS By Mehmet Atlar School of Marine Science & Technology, UK

2 Main objective of marine antifoulings Any vessel in the sea rapidly colonised by marine FOULING which can have severe impact on the economics of vessel operation through increased drag Preventing the attachment of fouling and hence minimising drag is the main objective of marine antifoulings There are other ways of keeping hulls clean (e.g. in-water scrubbing) but none so far proven to be viable for the vast majority of the world s fleet

3 Current issues facing ship operators Ever increasing and unpredictable fuel prices Operators are looking at cost more closely than ever New paint technologies and associated products Operators are confused by the claims and counter claims regarding to A/F IMO and National Legislation Operators have A/F high on the agenda by law The Environment matters more than ever Operators want to be environmentally compliant (ISO)

4 Outer hull condition - Hull Roughness Frictional resistance is largely controlled by the roughness on the outer hull Roughness on the outer hull caused by Mechanical (surface profile roughness due to e.g. corrosion, cold flow, detachment, repairs etc) Biological (Marine fouling)

5 Marine Fouling Types Plant Animal Microalgae (slime) Macroalgae (weeds) Soft Bodied Hard Shelled Red Brown Green Unlimited Limited Barnacles Tube Worms Mussels Chthamalus montagui Pomatoceros Mytilus (Barnacle) Cryptopleura ramosa Sea Hydroid triqueter Lettuce edulis (Tubeworm) (Common (Ulva) Mussel)

6 Marine fouling effects Slime (microfouling): 1~2% increase in drag Weed fouling: Up to 10% increase in drag Shell fouling: Up to 40% increase in drag Barnacles can cut through coatings Fouling can grow on top of other fouling

7 Antifouling technology options Biocidal technology Controlled Depletion Polymer (CDP) Self-Polishing Copolymer (SPC) Hybrid SPC Non-biocidal technology Foul Release (non-stick)

8 The regulatory position Most antifoulings are classed as biocidal products So they are regulated in the same way as are pesticides Biocide on paint surface Biocide in water column Biocide in sediments Degradation Degradation 3 Key environmental issues: Rate of biocide degradation Toxicity to non-target organisms Potential for bio-accumulation

9 IMO AFS Convention In October 2001 International Convention on the Control of Harmful Anti- Fouling Systems on Ships (IMO-AFS Convention) was declared This has banned the application of TBT paints from 1/1/2003 and the use (presence) of TBT paints on ships from 17/09/2008 Sealer coats can be used to overcoat TBT paints after 17/09/2008 (and so remove the presence of TBT as active antifoulings) Depending on ship size self certificate or International A/F certificate is required Classification societies can survey ships to issue interim certificate or SOC (Stat of Comps ) There are exemptions for naval ships, FPSO and FSU s

10 Biocidal Technology Controlled Depletion Polymers (CDP) Use of Rosin, or derivatives, in the biocide releasing mechanism via hydration Leached layers can become thick increasing roughness (~75μm) Higher volume solids content (55-60%) Film integrity is generally poor, and re-blasting is needed after 10 years But they are value for money for use in lower fouling are areas or for vessels with short dry-docking intervals (up to 36 months) Typical CDP (Bulker, 05/05, 24 mo.) Rough CDP surface after washing

11 Biocidal Technology Self Polishing Copolymers (SPC) Controlled chemical dissolution ( hydrolysis ) of the paint film presents thin leached layers (~10-15 μm) Therefore long dry-docking intervals (up to 60 months) and better smoothing Simple cleaning and re-coating at M & R Excellent weatherability, fouling control in outfitting and good mechanical properties Best A/F properties Cu Ac SPC CDP ULCC, 51 months in-service Container, 17 months in-service

12 Biocidal Technology Hybrid SPC Biocide releasing technology is a mixture of hydrolysis and hydration mechanisms, combining SPC acrylic polymer with a certain amount Rosin. Reasonable leached layer thickness (~25-30 μm) Therefore performance and price are mid-way between the CPD (rosin based) and SPC (Acrylic based) High volume solid content Duration: Vertical sides - up to 3 years; Flats up to 5 years Good A/F performance CDP Hybrid SPC Bulker, 35 months in-service Singapore raft test results

13 Biocidal Technology - Summary Self-Polishing Copolymer SPC PERFORMANCE Hybrid SPC CDP Controlled Depletion Polymer PRICE

14 Non-biocidal technology Foul Release (F/R) No biocide and hence no leaching; instead low surface energy material used with non-stick mechanism The most F/R systems use Silicone material based on Poly-Di-Methly- Siloxane (PDMS): Relative adhesion Strong Medium Low PDMS allows the polymer chain to readily adapt to the lowest surface energy configuration and hence low adhesion PDMS also presents an order of magnitude lower elasticity modulus These properties are most commonly correlated with resistance to biofouling. Relative Adhesion Relative adhesion PDMS Surface free energy in air (mn/m), γc (y.e)1/2 ( E) 1/ 2 γ c

15 Foul Release (F/R) - Surface resistance to adhesion The F/R properties of marine coatings are evaluated by measuring the adhesion of barnacles in shear Tests in Florida indicated that barnacle shear adhesion strength on F/R test plates was an order of magnitude lower than other surfaces (Corresponding speeds: 12 & 20 knots for two different FR surfaces) Before Testing After 4 knots for 1 min After 7.5 knots for 1 min After 12 knots for 1 min After 16.5 knots for 1 min After 20 knots for 1 min

16 F/R Coatings Features & Benefits Potential fuel savings and lower emissions No biocides Durable & Long lasting Low VOC Foul Release Less weight Antifouling Performance Less paint Keeps fouling off propellers Lower M&R costs

17 Newcastle University research on F/R coatings Comparative drag tests in towing tanks and rotor facility Boundary layer measurements in cavitation tunnels Surface characterisation Drag-Roughness correlations Propeller F/R coating research full-scale trials and observations

18 Main findings from Newcastle coating research Drag tests (in tanks / Rotor) confirmed that freshly applied F/R coating gave less drag increase with reference to the uncoated surface than the freshly applied SPC coating The roughness functions of the different surfaces from the BL tests indicated that on average the F/R surfaces exhibit less drag than SPC surfaces, which is in agreement with the findings from the towing tank and rotor experiments

19 Main findings Detailed roughness analysis revealed that the main difference between the F/R and SPC systems lies in the texture characteristics. Whereas the SPC surfaces display a typical closed texture, the Foul Release surface exhibits a wavy, open texture. Freshly sprayed F/R micron Freshly sprayed SPC Foul Release Roughness profile: Ra = 1.10 Rq = 1.21 Rt = 4.50 Sk = Ku = 5.04 Sa = mm SPC Roughness profile: Ra = 3.26 Rq = 4.04 Rt = Sk = 0.01 Ku = 3.29 Sa = micron mm

20 Main findings Correlation of roughness with drag for F/R coatings could not be done using solely a single roughness parameter. It is necessary to also include other parameters to include the effect of paint texture. Even the measurement of the single roughness parameter using a stylus based equipment (e.g. BMT Roughness Analyser) is extremely difficult and open to question for F/R coated hull surfaces. Measurement of texture parameters requires modification of this equipment as well as consideration of other measurement techniques (e.g. optical) implemented on a robust, industrial device.

21 Main findings The above findings are based on a limited brand, freshly applied F/R coatings. It is a well-known fact the performance characteristics of coatings in-service differs and the effect of slime on the F/R surfaces requires particular attention and hence further research Correlation studies require wealth of reliable hull roughness and performance data from full-scale. Such data on F/R coatings are currently scarce and requires advanced performance monitoring and analyses systems.

22 Main findings Application of F/R coatings on propellers prevents the increase in roughness over the time and has the beneficial effect of keeping propeller free from major fouling as clearly observed in full-scale. 14 months uncoated Newly coated After 12 months After 24 months After 36 months

23 Main findings % Frequency 40.00% 35.00% 30.00% 25.00% 20.00% 15.00% Ra Frequency Distribution for the Uncoated Propeller, the Newly Coated Propeller and after 1yr in Service New Coating Coating After 1yr in Service Uncoated Propeller 10.00% 5.00% 0.00% Ra value (microns) % Sm Frequency Distribution for the Uncoated propeller, Newly Applied Coating and After 1yr in Service 90.00% % Frequency 80.00% 70.00% 60.00% 50.00% 40.00% 30.00% New Coating 1yr in Service Uncoated Propeller 20.00% 10.00% 0.00% Sm Value (Microns)

24 Main findings Model tests in cavitation tunnel and dedicated trials in fullscale with freshly applied F/R coatings on propeller showed no conclusive evidence of any effect on efficiency, cavitation, noise Corrected Shaft Power (Watts) Final Power Curve Comparison Errors estimated at 10% Uncoated Trial Coated Trial Comparison of Open Water Characteristics in Atmospheric condition (water speed 4ms-1, Confidence limits 95%) uncoated Kt uncoated 10Kq uncoated Efficiency coated Kt coated 10Kq coated Efficiency Tide Corrected Speed over Ground (knots) Kt, 10Kq, Efficiency Advance Coefficient, J

25 Main findings Although there are numerous end-user claims for the benefits of F/R coatings on the propeller efficiency, cavitation, noise and vibration these do not have any scientific evidence. There is a need for advanced performance monitoring/ analysis systems and dedicated trials which are often impractical and difficult to perform for ship owners.

26 Recommendations to the ITTC community To establish reliable and meaningful experimental methods for the measurement and analysis of drag, boundary layer and surface characteristics of FR types anti-fouling systems To establish robust and practical means of measuring the surface topology of FR coated surfaces in full-scale To promote campaign for collecting credible full-scale trial data on the speedpower and surface characteristics of ships coated with FR systems To support correlation studies for the drag and dominant surface parameters of FR coated surfaces for practical roughness allowance parameters dedicated for these surfaces Explore the effect of FR coatings on the propeller and other appendages not only for efficiency but also for cavitation and noise Be aware of the undesirable effect of slime and look for experimental and fullscale means of exploring this effect. Can CFD be help for exploring the effect of coatings?

27 Acknowledgement Discusser gratefully acknowledges the financial support received from International Paint Ltd (Akzo Nobel) in conducting the past and current coating research in the School of Marine Science and Technology, Newcastle University, UK