AN UPDATE ON MARINE ANTIFOULINGS By Mehmet Atlar School of Marine - - PowerPoint PPT Presentation

25th 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

Microalgae (slime)

Animal Plant

Macroalgae (weeds) Soft Bodied Hard Shelled Red Brown Green Unlimited Limited Barnacles Mussels Tube Worms

Cryptopleura ramosa Sea Lettuce (Ulva) Hydroid Chthamalus montagui (Barnacle) Pomatoceros triqueter (Tubeworm) Mytilus edulis (Common Mussel)

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
• ther 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

Degradation Degradation Biocide Biocide on paint surface Biocide Biocide in water column Biocide Biocide in sediments Degradation Degradation

• Most antifoulings

are classed as biocidal products

• So they are regulated in the same way as are pesticides

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
• f TBT paints from 1/1/2003

and the use (presence)

• f 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”
• r

“International A/F certificate” is required

• Classification societies can survey ships

to issue interim certificate or SOC (Stat’

• f Comps’)
• There are exemptions for naval ships, FPSO and

FSU s

Biocidal Technology – Controlled Depletion Polymers (CDP)

• Use of Rosin,
• r 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

• r for

vessels with short dry-docking intervals (up to 36 months)

Typical CDP (Bulker, 05/05, 24 mo.) Rough CDP surface after washing

• 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

Biocidal Technology – Self Polishing Copolymers (SPC)

ULCC, 51 months in-service Container, 17 months in-service

Cu Ac SPC

CDP

• 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

Biocidal Technology – Hybrid SPC

Bulker, 35 months in-service Singapore raft test results

Hybrid SPC CDP

Hybrid SPC PRICE PERFORMANCE SPC CDP “Controlled Depletion Polymer” “Self-Polishing Copolymer”

Biocidal Technology - Summary

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):

– 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.

PDMS Surface free energy in air (mN/m), γc Relative adhesion

Strong Medium Low

2 4 6 8 10 12 14 (y.E)1/2 Relative Adhesion

( )

2 / 1

E

c

γ

Relative adhesion

Foul Release (F/R) - Surface resistance to adhesion

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 Before Testing

• The F/R properties
• f marine coatings are evaluated by measuring the

adhesion of barnacles in shear

• Tests in Florida indicated that barnacle shear adhesion strength
• n F/R test

plates was an order of magnitude lower than other surfaces (Corresponding speeds: 12 & 20 knots for two different FR surfaces)

F/R Coatings – Features & Benefits

Foul Release

No biocides Antifouling Performance Lower M&R costs Low VOC Potential fuel savings and lower emissions Durable & Long lasting Less paint Less weight Keeps fouling off propellers

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
• f 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

SPC Roughness profile: Ra = 3.26 Rq = 4.04 Rt = 19.98 Sk = 0.01 Ku = 3.29 Sa = 1.90

• 15
• 10
• 5

5 10 15 20 5 10 15 20 25 30 35 40 45 50 mm micron

Foul Release Roughness profile: Ra = 1.10 Rq = 1.21 Rt = 4.50 Sk = -0.87 Ku = 5.04 Sa = 0.23

• 15
• 10
• 5

5 10 15 20 5 10 15 20 25 30 35 40 45 50 mm micron

• 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.

Main findings

Freshly sprayed SPC Freshly sprayed F/R

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

• f texture parameters requires

modification of this equipment as well as consideration of other measurement techniques (e.g.

• ptical) implemented on a robust,

industrial device.

• 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

• n the F/R surfaces

requires particular attention and hence further research

• Correlation studies require wealth
• f 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

Main findings

• Application of F/R coatings on propellers

prevents the increase in roughness

• ver

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 24 months After 12 months After 36 months

Main findings

Ra Frequency Distribution for the Uncoated Propeller, the Newly Coated Propeller and after 1yr in Service

0.00% 5.00% 10.00% 15.00% 20.00% 25.00% 30.00% 35.00% 40.00% 2 4 6 8 10 12 14 16 18 20 22 24 26 28

Ra value (microns) % Frequency

New Coating Coating After 1yr in Service Uncoated Propeller

Sm Frequency Distribution for the Uncoated propeller, Newly Applied Coating and After 1yr in Service

0.00% 10.00% 20.00% 30.00% 40.00% 50.00% 60.00% 70.00% 80.00% 90.00% 100.00% 500 1000 1500 2000 2500 3000 3500 4000

Sm Value (Microns) % Frequency New Coating 1yr in Service Uncoated Propeller

• Model tests

in cavitation tunnel and dedicated trials in full- scale with freshly applied F/R coatings on propeller showed no conclusive evidence of any effect on efficiency, cavitation, noise

Final Power Curve Comparison

Errors estimated at 10%

0.00 20000.00 40000.00 60000.00 80000.00 100000.00 120000.00 140000.00 6.00 6.50 7.00 7.50 8.00 8.50 9.00 9.50

Tide Corrected Speed over Ground (knots) Corrected Shaft Power (Watts)

Uncoated Trial Coated Trial

Comparison of Open Water Characteristics in Atmospheric condition (water speed 4ms-1, Confidence limits 95%)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.25 0.35 0.45 0.55 0.65 0.75 0.85 Advance Coefficient, J Kt, 10Kq, Efficiency uncoated Kt uncoated 10Kq uncoated Efficiency coated Kt coated 10Kq coated Efficiency

Main findings

• Although there are numerous

end-user claims for the benefits

• f 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

• wners.

Main findings

• To establish reliable and meaningful experimental methods for the

measurement and analysis of drag, boundary layer and surface characteristics

• f 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 speed-

power 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
• nly for efficiency but also for cavitation and noise
• Be aware of the undesirable effect of slime and look for experimental and full-

scale means of exploring this effect.

• Can CFD be help for exploring the effect of coatings?

Recommendations to the ITTC community

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