25th ITTC Group Discussions 3 – Global Warming and Impact on ITTC Activities

AN UPDATE ON MARINE ANTIFOULINGS

ByMehmet 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)

AnimalPlant

Macroalgae(weeds) Soft Bodied Hard Shelled

Red Brown Green Unlimited Limited Barnacles MusselsTube Worms

Cryptopleura ramosaSea Lettuce(Ulva)

HydroidChthamalus 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 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

DegradationDegradation

BiocideBiocide on paint surface

BiocideBiocide in water column

BiocideBiocide in sediments DegradationDegradation

•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

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 shipsto issue interim certificate or SOC (Stat’

of Comps’)

•

There are exemptions for naval ships, FPSO andFSU 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 (~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

•

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 SPCCDP

Hybrid SPC

PRICE

PER

FOR

MA

NC

E

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

Rel

ativ

e ad

hesi

on

Strong

Medium

Low

0 2 4 6 8 10 12 14

(y.E)1/2

Rel

ativ

e Ad

hesi

on

( ) 2/1Ecγ

Rel

ativ

e ad

hesi

on

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

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)

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

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

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

-15

-10

-5

0

5

10

15

20

0 5 10 15 20 25 30 35 40 45 50

mm

mic

ron

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

-15

-10

-5

0

5

10

15

20

0 5 10 15 20 25 30 35 40 45 50

mm

mic

ron

•

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 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.

•

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

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 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%

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28Ra value (microns)

% F

requ

ency

New CoatingCoating After 1yr in ServiceUncoated 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%

0 500 1000 1500 2000 2500 3000 3500 4000

Sm Value (Microns)

% F

requ

ency

New Coating1yr in ServiceUncoated 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 ComparisonErrors 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)C

orre

cted

Sha

ft P

ower

(Wat

ts) Uncoated Trial

Coated Trial

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

0

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,

10K

q, E

ffici

ency

uncoated Ktuncoated 10Kquncoated Efficiencycoated Ktcoated 10Kqcoated Efficiency

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.

Main findings

•

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 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 only 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