Ship hull biofouling has significant impacts on fleet readiness, ship performance, cost, and the environment. Biofouling results in increased hydrodynamic drag which results in greater fuel use and greater emissions per distance traveled than a hydraulically-smooth hull. A study by Schultz, et al. found the typical fouling rating (FR) of a US Navy DDG-51 class vessel, FR-30, increases fuel consumption by 10.3% over a hydraulically-smooth DDG-51. Results showed that reducing this fouling rating to FR-20 would lead to savings of $340K per ship and more than double that when the hull was kept at a fouling rating of FR-10, saving the US Navy nearly $800K per hull annually. And while such studies on commercial vessels are almost nonexistent, similar economic impacts of fouling are certain. A recent report cited the EMMA MAERSK, a 397m container vessel, estimated spending approximately $20K per day in propulsive fuel lost to biofouling.
The economic impact of fouling is also due to costly conventional cleaning and containment activities . A study in 2016 commissioned by the US Coast Guard, determined the cost to remove light biofouling from a ship’s hull to be $0.33 per ft2 (approximately $3.55 per m2). Based on that estimate, complete biofouling removal from a DDG-51 would run more than $10k, while the cost to remove biofouling from a Panamax class container ship would run more than $98K. These estimates are for traditional cleaning methods, which degrade the ablative coatings used for anti-fouling, leading to dry-docking for re-coating once every few years. Dry-docking a large ship may run as much as $1M-$2M.
Fouling also has significant environmental impacts, from greenhouse gas emissions associated with increased propulsive fuel costs, to the toxins released by in-water cleaning. Many countries are now requiring containment of in-water cleaning or prohibiting the practice while in port. The traditional, intense cleaning processes used to clean fouled hulls are costly, inefficient for operations, damaging to the hull coating, and environmentally unacceptable. An alternative to the reactionary intense cleaning process is the regular and thorough disruption of growth on the ship hull coating by gentle brushing with small soft-bristled brushes. This process, referred to as hull grooming, akin to brushing one’s teeth every day to avoid a monthly dentist visit and annual root canal. Research led by Dr. Geoffrey Swain at Florida Institute of Technology’s Center for Corrosion and Biofouling Control (FIT CCBC) has pioneered the methodology and practice of hull grooming, demonstrating it to be a cost-effective practice to control biofouling, while releasing far fewer toxins into the water than cleaning. Because hull grooming only lightly brushes the ship hull and does not remove coating, containment is not necessary and the life of the original coating is extended, lengthening the period between costly dry docking. Additionally, hull grooming is done with light-weight brushes making very gentle contact on the ship hull. This permits hand-held brushes that can easily be operated by divers or even brush tools that can be operated by small hull-crawling robots. The lack of need for heavy equipment to launch and recover a cleaning tool, further adds to the cost-benefit.
Source: https://www.marinelink.com/