FOULING. It is estimated that there are in excess of 4,000 known fouling species, all of which have the potential to colonise a submerged surface.

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1 FOULING Fouling is the term generally used to describe the settlement and growth of marine plants and animals on submerged structures. These structures typically include ships hulls, piers, piling and oil rigs, but also includes the internals of pipework used to carry water as a coolant for industrial power plants. It is estimated that there are in excess of 4,000 known fouling species, all of which have the potential to colonise a submerged surface.

2 Animal Fouling Barnacles They are the most commonly encountered animal fouling. Barnacle larvae are selective in their site for settlement and appear to recognise other barnacles. This results in barnacles settling close to other members of the species which aids in cross fertilisation. Barnacles live within hard shells which can adhere very tightly and can be difficult to remove. On ships, removal by underwater scrubbing or mechanical scraping typically results in a barnacle residue being left behind. This can promote further colonisation, increasing the fouling problem.

3 Animal Fouling contd.. Hydroids Plant like in appearance, hydroids live in colonies and are often found on the flat bottom of vessels where they are often mistaken for algae. Due to the low light levels on flat bottom areas, however, it is a safe assumption that filamental growth on the flat bottom is likely to be a type of hydroid and not algae.

4 Animal Fouling contd.. Tube worms These organisms live in easily recognisable calcareous tubes which protect their soft bodies. Tube worm larvae can recognise their own species resulting in large colonies being established. They tend to settle on stationary structures or on vessels which spend a comparatively longer time in port. Animal fouling does not require light to grow and can proliferate on any area of an underwater hull, including the flat bottom.

5 Plant (Weed) Fouling The most common plant fouling on ships is the brown algae and the green algae, often referred to as sea grass due to its similar appearance and colour. Polycellular algae begins with the settlement of microscopic spores. These spores can settle in seconds and colonise a submerged surface within hours. Plant fouling usually occurs where there is available sunlight, i.e. around the water line and a few metres below. It is not usually found on the flat bottom of vessels.

6 Slime fouling Slime (a generic term covering many types of marine organisms) on submerged surfaces is attributable to the accumulation of unicellular algae (diatoms). Difficult to stop them settling on the underwater hulls of vessels, slime has a very low surface profile and can remain adherent on ships hulls at speeds in excess of 30 knots. Slime: consisting of diatoms

7 Fouling adhesion Fouling species adhere to submerged surfaces by means of an adhesive. Initial attachment and development of the adhesive bond is a complex process. Although it has been proven that seaweed spores and certain gooseneck barnacle larvae are capable of attaching in water flows of up to 10 knots, the bulk of fouling attachment on ships hulls occurs when the vessel is slow moving or stationary. The essel s trading pattern and operational profile, i.e. speed and activity, will determine the risk of fouling and the type, extent and severity of fouling which could develop.

8 Factors On ships hulls, fouling type, extent and severity depends upon many factors, e.g. water salinity, light, temperature, pollution and nutrient availability. The severity of fouling tends to be a seasonal phenomenon governed by geographical location e.g.: Polar zones: <50C, low fouling risk. Fouling will occur for a short time period, typically either side of mid summer. Temperate zones: 5-200C, medium fouling risk. Fouling will occur throughout the year peaking in spring to early autumn. Tropical/sub tropical zones: 200C+, high fouling risk. Fouling continues throughout the year with a multiplicity of species.

9 Factors contd.. Vessels trading extensively in tropical or sub tropical waters are subjected to the most severe fouling attack, particularly in more shallow, coastal waters where there is a greater abundance of light, heat and nutrients, resulting in prolific reproduction of the fouling species. Understanding where a vessel trades is important because this can identify the likely fouling challenge or fouling risk a vessel may experience in service. Vessels at greatest risk are those slow moving, low activity vessels trading extensively in tropical or sub tropical coastal waters, e.g.: Lo speed essels < k Lo acti ity essels, 5 % statio ary Locally tradi g coastal essels Faster, more active deep sea vessels are also at risk in tropical or sub tropical coastal environments depending upon the frequency of port calls and the percentage port time.

10 Factors contd.. Figure: Port classification

11 The most common means to control fouling is through the use of antifouling paints.

12 Antifouling Paints The most remarkable success against marine biofouling can be ascribed to TBT antifouling paints. Self-polishing copolymer (SPC) TBT systems had been widely used since 1960 s until 2000 s due to its perfect antifouling ability. Nevertheless, research activities demonstrated that TBT exposure causes shell malformation of oysters. Moreover, TBT compounds persist in the water, show toxic effects to marine organisms even with a low concentration; also it may accumulate in marine organisms and hence enter the food chain. As a consequence, IMO banned the applications of antifouling coatings which contain TBT in 2003 and the operations of ships coated with TBT paints in 2008.

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19 Table : Historical development of the antifouling strategies

20 Antifouling Paint Today, there are several types (TBT free foul control technology) of coatings available to mitigate fouling and they can be classified into two main categories based on their compositions; namely, biocidal and non-biocidal coatings. Biocidal coatings can be listed as Controlled Depletion Polymer (CDP), Self-Polishing Copolymer (SPC) and Hybrid PC. Non-biocidal coatings are foul-release coatings (FR), which are also called non-stick coatings.

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22 Controlled Depletion Polymer (CDP) CDPs usually have high VOC(volatile organic content) of 50-60% and use rosin or its derivatives in the biocide releasing mechanism by hydration process. Rosin(~90% Abietic Acid) comes from trees, and has been used for over 100 years in antifouling paints. Rosin can be used at low level to form hard Insoluble Matrix antifoulings, or high level to form soft Soluble Matrix antifoulings. Modern Soluble Matrix antifoulings are commonly referred to as Controlled Depletion Polymer (CDP) antifoulings.

23 Controlled Depletion Polymer (CDP) contd.. Rosin has some disadvantages: it is a brittle material, and can cause cracking and detachment it reacts with oxygen and has to be immersed relatively quickly it does not prevent water going into the depth of the antifouling paint Porous leached layers thicken in time and increase surface roughness to about 75 microns. They require blasting after 10 years of use. However, they are suitable for vessels with short dry-docking intervals (up to 3 years) and regions having lower fouling rates.

24 Self Polishing Copolymers (SPC) Self-Polishing Copolymer (SPC) undergo a reaction ( hydrolysis ) with sea-water, to form an acid polymer which is then soluble in sea water. This results in thinner leached layers and thus much better control of biocide release:

25 Self Polishing Copolymers (SPC) contd.. Unlike CDP s, their leached layers are much thinner, about 1015 microns. Thus, they offer a smoother surface and longer drydocking intervals. SPC s show great antifouling properties and are easy to clean and may be repaired during maintenance. Ideal for newbuildings: excellent weatherability fouling control during fitting out good mechanical properties

26 Hybrid SPC Hybrid SPC s, which combines SPC acrylic polymer with rosin, have a hybrid biocide releasing mechanism between hydrolysis and hydration. They contain high VOC and have a reasonable leached layer thickness of about microns. As far as the performance is concerned, they lie somewhere between CPD and SPC. Their life runs somewhere between 35 years.

27 Foul release (FR) coatings FR coatings, on the other hand, prevent the attachment of marine species on hull owing to surface properties. Nevertheless, the term foul releasing is misleading because FR coatings could not release all of the slime and they are effective only above a certain speed since the releasing mechanism works by means of a particular amount of shear force to detach the marine organisms. Because of this, they are not appropriate for slow ships and for the ships spending long time in ports. Also, they are very expensive compared to the other types of coatings and may be damaged easily due to hard shelled fouling organisms or any mechanic effects such as cleaning.

28 Foul release (FR) coatings contd..

29 Properties of the existing hull coatings

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31 Effect of roughness and coating on ship resistance Surface roughness of the underwater part of a ship is extremely important in terms of economic considerations. The frictional resistance of a ship is influential on the fuel consumption of the vessel. There are many factors such as physical damages and fouling which affect hull roughness. Undue mechanical damages may be mitigated to a degree. However, fouling poses a big problem to deal with during service life between dry-docking intervals. Studies have shown that hard-shell fouling may increase the resistance up to 40%. Therefore, proper fouling control is of paramount importance for both design life and fuel economy of the ship.

32 Effect of roughness and coating on ship resistance contd.. The new generation toxic-free antifouling systems have been emerging in the commercial market even before IMO s TBT ban. Choosing an appropriate antifouling system for a ship depends mostly on the operational characteristics of that particular ship. There are advantages and disadvantages of each antifouling paint system. Some studies show that foul release antifouling paints have less drag than tin-free SPC antifouling paints. Finally, appropriate antifouling paint systems must be used to reduce hard-shell and slime fouling in order to reduce drag and lower fuel consumption. Although a lot of progress has been achieved in antifouling paint technology, there are still lot to be done to find a meaningful correlation between hull roughness and fuel penalty.

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