Nano Additive-based Foul Release Hull Coatings for Improved Maritime Vessel Performanc

Biofouling is a significant economic concern for marine industries. The microorganisms adhere to the surface of marine bodies (e.g., ships, boats) and result in increased hydrodynamic drag and reduced fuel efficiency. Coatings used on marine bodies are not entirely resistant to biofouling, and many of the newly developed coating technologies like tributyltin self-polishing co-polymers (TBT-SPC) coating, copper, and zinc coatings severely affect the environment through the steady release of TBT toxin and leaching of copper and zinc metals respectively. Banning of these coatings by International Maritime Organization (IMO) triggered the search for new alternative coating solutions for biofouling reduction. In this research, we focused on developing improved foul release hull coatings by using environmentally benign and low-cost nano-additive based silicone hull coatings. Commercial nanopowders of X, Y (confidential or proprietary information), vanadium oxide (V2O5), molybdenum disulfide (MoS2) and conventional graphite, were used as additives to the commercial silicone-based hull coatings for improved foul releasing characteristics as well as reduced hydrodynamic drag. Nano-additives were characterized for phase, crystallinity, and internal microstructural features using X-ray diffraction and transmission electron microscopy. Coatings were also evaluated for hydrophobicity, and surface morphologies (e.g., surface roughness, dispersion of nanoparticles) using wetting angle measurements and scanning electron microscopy. Anti-microbial and biofouling evaluation of composite coatings were carried out in seawater to check hydrophobicity and foul release characteristics. These coatings were further tested for hydrodynamic drag on an inhouse built friction disk machine to check the change in hydrodynamic drag before and after biofouling experiments. Composite coatings with X and Y nano-additives yielded the best results for anti-biofouling hydrodynamic drag characteristics. Superhydrophobicity with no microbial growth and improved foul releasing characteristics with a least change in hydrodynamic drag were observed after all the tests. Whereas other coatings showed moderate to no improvement in the anti-biofouling and drag characteristics. Coatings without nano-additives showed the worst performance with highly affected surfaces by microbial growth and increased hydrodynamic drag. By replacing the expensive commercial paints around 2% with inexpensive nano-additives can save a lot of money for huge maritime vessels and cut down the biofouling problems. These results also indicate that the usage of nano-additives to the existing silicone-based coatings can serve as an environmentally benign and inexpensive solution for improvement of ship propulsion and can even reduce the amount of paints used for coatings and hence, will enhance the overall performance of the maritime vessels.