Hulls that glide through the water like sharks – and stay smooth
The potential of drag reduction through a textured surface is widely known. In real world scenarios, however, the advantages are quickly negated if fouling control properties are not integrated. A new project developed a biocide-free solution to this problem.
The European “Seafront” project aims to merge and validate these two essential characteristics in a relevant environment. Lab testing shows a five to six percent additional drag reduction for textured coatings compared to a hydrodynamically smooth uncoated surface. Project leader Clayton Price of Akzo Nobel explains: “Potentially the improvement over a traditional coated surface would be greater, although the complexity associated with application and alignment of the riblet surface to a ship's hull will likely reduce this. Under normal operational conditions, a drag reduction in the order of two to four percent as compared to the current best available technology should, however, still be possible.”
Potential fuel cost savings are massive along with the positive impact on the environment. The maritime sector currently uses the most polluting fractions in fossil fuels. This sector contributes more to carbon dioxide emission than Germany as a country does. Potential savings can be estimated at three billion dollars and several tens of millions of metric tons of CO2emissions. Enabling this reduction would mean a big step for global carbon dioxide emission reduction.
Non-biocidal antifouling
Specialist from multiple European companies and scientific institutes joined forces in the Seafront project in the Work Packages Physical modification of the surface structure (riblets, WP1), Surface chemistry (lubricous furfaces, WP2) and Bio-active (WP3). Fraunhofer IFAM in Bremen has been involved in all three WPs, but its biggest contribution was the riblet/sharkskin coating.
Scanning electron microscopy image of the riblet-textured coating (Source: Fraunhofer IFAM)
The institute developed a process to actually make riblets in coating and the aerospace application of it is going into production. Project manager Dorothea Stübing explains: “We still need to develop an industrial process to make large scale application of this technology for the maritime sector feasible, but that's what we are going to do together with AkzoNobel. We are currently applying systems for testing.”
Akzo Nobel’s existing non-biocidal fouling control technology was integrated into the riblet coating. Integration of antifouling technology based on rubbery fluoropolymer elastomers developed by Solvay, developed in WP2 of the project, is an obvious next step. The fluoropolymer could provide a much wanted solution, because it works as an non-biocidal fouling control system.
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Pier Antonio Guarda, project leader at Solvay Specialty Chemicals explains: “In one material variant, we created a simultaneously positively and negatively charged fluoropolymer that turned out to be important to the whole project and we were very glad to have been able to contribute this.”
New Coating in the field
Combining riblet drag reducing texture with non-biocidal fouling control technology will really mean a big step ahead for the maritime sector. Akzo Nobel already initiated the first phase of this within the project, having recently completed the application of a benchmarked prototype coating system onto an 1:4 scale model of an underwater kite in a tidal energy application of Swedish company Minesto.”
Inspection of AkzoNobel coatings at Dubai Dry Dock (Source: Akzo Nobel)
Minesto is a Swedish company dedicated to harvesting renewable tidal energy with subsea kites specificaly designed for low velocity currents and as one could imagine, biofouling is an important factor for long lasting efficiency of marine energy systems.
The kite will be tested at Strangford Lough near Northern Ireland. Apart from that, operational testing on several pleasure crafts, a fishing vessel and offshore equipment is ongoing. A third application involves the frames and nets of aquaculture structures.
Interesting outcomes in fishnet coating
One of the sectors that is alsovery interested in the outcomes of the Seafront project is aquaculture. If fishnets should be fouled, this poses three main problems. It would prevent the current of fresh, oxygen-rich water to enter the circles in which the fish are kept. Furthermore, especially mussel growth would make the nets so heavy, that these run the risk of breaking when hauled from the water. Finally, fouling organisms such as hydrates and brown and green algae might host sea lice larvae and other pests that could infect the fish.
Typical Norwegian salmon farm with 160 meters circumference cages, located in Mid Norway. (Source: Sinkaberg Hansen)
That is why the nets are treated against fouling. Halvor Mortensen, project leader at Norwegian R&D organization Val FoU, involved in a Seafront pilot project comments: “The present state-of-the-art is dipping of fishnets in copper based coatings. Regretfully, the biocidal heavy metal is emitted to the environment. It is therefore not an acceptable solution for a sector that wishes to contribute to a sustainable food supply.
The sector is looking for alternatives. This explains why Val FoU, exploiting an aquaculture farm with secondary school students, was already involved in Seafronts predecessor-project Ambio. AkzoNobel International Paint invited Val FoU to also join the Seafront Consortium. After some testing in 2015, tests with an improved version of the coating were performed in 2017.
For further Information about the project and a list of all participating companies and institute visit www-seafront-project.eu
