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
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
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)
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)
Marine Fouling Types Plant Animal Macroalgae Microalgae (weeds) Soft Bodied Hard Shelled (slime) Red Brown Green Unlimited Limited Barnacles Tube Worms Mussels Chthamalus montagui Mytilus edulis Pomatoceros triqueter Sea Lettuce Hydroid Cryptopleura ramosa (Barnacle) (Common Mussel) (Tubeworm) (Ulva)
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
Antifouling technology options • Biocidal technology – Controlled Depletion Polymer (CDP) – Self-Polishing Copolymer (SPC) – Hybrid SPC • Non-biocidal technology – Foul Release (non-stick)
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 Biocide in water column Biocide Degradation Degradation Biocide in sediments Biocide Degradation Degradation 3 Key environmental issues: •Rate of biocide degradation •Toxicity to non-target organisms •Potential for bio-accumulation
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
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 (~75 μ m) • 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) Rough CDP surface after washing Typical CDP (Bulker, 05/05, 24 mo.)
Biocidal Technology – Self Polishing Copolymers (SPC) • Controlled chemical dissolution (“hydrolysis”) of the paint film presents thin leached layers (~10-15 μ m) • 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 CDP Cu Ac SPC ULCC, 51 months in-service Container, 17 months in-service
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 μ m) • 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
Biocidal Technology - Summary “ Self-Polishing Copolymer” SPC PERFORMANCE Hybrid SPC CDP “Controlled Depletion Polymer” PRICE
Non-biocidal technology – Foul Release (F/R) • No biocide and hence no leaching; Strong instead low surface energy material Relative adhesion used with “non-stick” mechanism • The most F/R systems use “Silicone” Medium material based on Poly-Di-Methly- Siloxane (PDMS): Low PDMS Surface free energy in air (mN/m), γ c – PDMS allows the polymer chain to readily adapt to “the lowest surface energy configuration” and hence low adhesion – PDMS also presents an order of Relative Adhesion Relative adhesion magnitude lower elasticity modulus • These properties are most commonly correlated with resistance to biofouling. 0 2 4 6 8 10 12 14 ( ) γ 1 / 2 E (y.E)1/2 c
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
F/R Coatings – Features & Benefits Potential fuel savings and lower emissions Durable & Long lasting No biocides Low VOC Less weight Foul Release Less paint Antifouling Performance Keeps fouling off propellers Lower M&R costs
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
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
Freshly sprayed F/R Main Foul Release Roughness profile: Ra = 1.10 Rq = 1.21 findings Rt = 4.50 Sk = -0.87 Ku = 5.04 Sa = 0.23 20 15 • Detailed roughness 10 analysis revealed that the 5 micron 0 0 5 10 15 20 25 30 35 40 45 50 main difference between the -5 -10 F/R and SPC systems lies in -15 mm the texture characteristics. Whereas the SPC surfaces Freshly sprayed SPC display a typical ‘closed SPC Roughness profile: texture’, the Foul Release Ra = 3.26 Rq = 4.04 surface exhibits a wavy, ‘open’ Rt = 19.98 texture. Sk = 0.01 Ku = 3.29 Sa = 1.90 20 15 10 5 micron 0 0 5 10 15 20 25 30 35 40 45 50 -5 -10 -15 mm
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.
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.
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
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