Kianejad SS*, Seif MS and Ansarifard N
Center of excellent in hydrodynamics and dynamic of marine vehicles, Australia
Received: 27 November, 2015; Accepted: 14 December, 2015; Published: 16 December, 2015
Seyed Sadreddin Kianejad, 2/5-7, newnham close, newnham, newnham, Launceston, Tasmania, Australia, Tel: +61470587216: E-mai:
Kianejad SS, Seif MS, Ansarifard N (2016) Experimental Study of Impact of Foul Release with Low Surface Energy on Ship Resistance. J Civ Eng Environ Sci 2(1): 005-010. 10.17352/2455-2976.000008
© 2015 Kianejad SS, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
A comparison between coating frictional resistances of several ship hulls has been conducted by experimental studies (Foul Release and conventional paint) in the unfouled conditions in Hydrodynamic open water tests in a lake using a ship model test.
Models are completely similar, in order to eliminate other factors of resistance such as wave-making resistance and viscous pressure resistance. Foul Release systems based on silicon offer a low surface energy and smooth surface that prevents adhesion of fouling organisms on underwater hulls. Wall roughness measurement was carried out by roughness analyzer and there is not much difference between Foul Release and conventional paint roughness. The results indicate that model with low surface energy has lower resistance compared to model with higher energy surface.
The most widely applied marine antifouling's is Tributyl-Tin Self-Polishing Co-Polymers (TBT-SPC), which can keep a surface of ship free of fouling for 5 years by means of a steady release of the TBT toxin. Due to environmental side-effects related to TBT, the International Maritime Organization (IMO) decided in October 2001 to phase out the use of TBT-SPCs until 2008. There are currently two alternatives on the market that can also offer 5 years of satisfactory antifouling performance. The first alternative, Tin-free SPC, uses the same chemical principle, but instead of TBT, gradually leaches copper-based toxins which are complemented by so-called “booster biocides”. The second type, Foul Release coatings, works by an entirely different principle. Instead of killing marine organisms that have attached to the hull, they try to prevent the stick of the fouling by providing a low surface energy onto which organisms have great difficulty attaching. If vessels are stationary for short times, settlement can occur, but there is only weak bonding between the fouling and the Foul Release coating surface and so the organisms can be relatively easily removed, by the hydrodynamic forces against the surface when the vessel is travelling fast enough. The Foul Release coatings described in this paper are silicone elastomers based. Experimental studies on the attachment of fouling organisms to different types of materials have shown that silicones are least prone to foul [1,2]. Eventually, all surfaces will foul, but experiments have also shown that the strength of attachment of the organisms on silicones is lower than other materials. Kovach and Swain towed a plate, which was coated with a Foul Release system and covered by fouling, at different speeds and showed that the organisms started to release at speeds above 12 knots . These antifoulings are therefore particularly suited for ships which spend a short time in port and travel at sufficiently high speeds.
The hull condition has important effect on the operation of marine vehicles. Highlighting the impact of Skin friction on some displacement ships, it has the share of about 90% of the total drag even in absence of hull fouling . Hence, understanding and predicting of frictional drag must be the seat of focus in this research. To find out the influence of surface roughness on the frictional drag of marine paints, some investigations was conducted by Musker , Townsin et al. , Granville , Medhurst , Grigson  and Schultz . Most of these studies were concentrated on analyzing the change in roughness and drag of the self-polishing copolymer (SPC) TBT systems, probably because of persistent fouling control against minimal fouling settlement in the TBT systems. A substantial part of research has been dedicated to studying the effects of fouling on drag specially the calcareous macro fouling (barnacles, oysters, etc.) and is reviewed in Marine Fouling and its prevention . Focusing on the effect of plant fouling and biofilms, as well, date back to McEntee . Moreover, further studies to acquire higher quantify of slime films effect on drag were carried out by Picologlou et al. . To detect the effect of fouling on the drag of copper-based coatings full-scale ship tests were performed by Haslbeck and Bohlander . Schultz and Swain  and Schultz  studied the details of turbulent boundary layers developing over biofilms and filamentous algae, respectively, using laser Doppler velocimetry. As a consequent, all of these studies showed that relatively thin fouling layers can significantly enhance the drag.
In some primary data from Candries et al. it can be seen that despite having a lower mean roughness in the unfouled condition, fouling-release systems may have slightly less frictional resistance than traditional Antifuling coatings .
There are little data to investigate effect of energy surface on ship resistance. The objective of present experimental investigation is to study effect of energy surface on ship resistance. The details of method and results of model test have been explained in the next sections.
A large number of Foul Release coatings that are in use today are based on silicone, with an extremely flexible backbone, which allows the polymer chain to readily adapt to the lowest surface energy configuration. The size of the free surface energy represents the capability of the surface to interact with other materials. Figure 1 shows relationship between relative adhesion and free surface energy. It was found experimentally that the relative adhesion of fouling organisms on a material is directly proportional to √ where by E is the elastic modulus of the material, and y is surface energy, direct relationship between relative adhesions and √ has been established, as shown in Figure 2 . Surface energy of silicone materials is at least an order of magnitude smaller than for other materials. Moreover, if organisms eventually do attach to the surface with foul release coating, it has been shown that they attach less strongly than on other materials (provided the coating is applied thickly enough), which explains why fouling organisms can release from the surface under the influence of hydrodynamic forces. An effective Foul Release coating relies on the smoothness of its surface. Surface free energy and the surface area available for adsorption and attachment of fouling organisms increase with roughness. The valleys of rough surfaces are penetrated by marine adhesives, therefore fouling will more readily attach. Moreover, the fouling also finds shelter from shear and abrasion in the crevices and thus roughness also poses a threat to the hydrodynamic removal of the organisms. Because of the fact that fouling organisms attach less quickly and less strongly on Foul Release surfaces it could be expected that the material is in some ways smoother than most surfaces. In turn this could explain why Foul Release surfaces exhibit less drag than other surfaces.