Ultrasonic Antifouling

Biofouling, the growth of marine organisms on in-water surfaces, is a perpetual and significant concern for all vessels. Hull biofouling can slow vessel speed, requiring the vessel to consume more fuel, resulting in an increased emission of greenhouse gasses. In addition to increasing drag on a vessel, biofouling by marine organisms within pipes can lead to system failures. Commercial shipping is responsible for nearly three percent of annual global greenhouse gas emissions, producing roughly as much carbon each year as the aviation industry. Therefore, technology that can reduce emissions is desirable. Further, biofouling in ballast areas and on the hull can transfer invasive species between water bodies.

To combat biofouling, various techniques have been utilized historically. The earliest mention of biofouling has been found in an Aristotle publication (4th century B.C.) (WHOI, 1952). Aristotle described the problem of Remora attaching to ships. Ship hulls of this era would need to be regularly scraped to remove the fish as well as adhered shellfish. There are reports in the historical record that the Phoenicians and Carthaginians used pitch on their ships’ bottoms to prevent biofouling. Other historical mitigation strategies included the application of wax, tar, and an early form of asphalt, and the application of copper sheaths to hulls.

Later antifouling strategies included the use of hull paints containing copper and other compounds, which were found to deter the settling of larvae and algae on the hull. The issue with this strategy is that the toxins (most frequently cuprous oxide) in the antifouling hull paint leach into the water. Cuprous oxide is a neurotoxin and can deter or even kill marine life drifting in leachate found in the ship’s wake.

Ultrasonic antifouling systems were developed to reduce the need for repeated applications of antifouling hull paint. It was found (Lee et al., 2001; Zhang et al., 2006) that gas vacuoles inside blue green algae collapsed if exposed to ultrasound for 1 to 5 minutes, killing the algae. Exposure to ultrasound also affects the ability of barnacles to settle on surfaces (Guo et al., 2011).

Ultrasonic antifouling systems work by emitting a low-powered, ultrasonic pulse via a transducer, frequently attached to the inside of the hull. The emitted pulse is intended to inhibit the growth of marine organisms on or near the vessel. However, the sound has been found to propagate distances up to 3 km away from the transducer (Trickey et al., 2022).

Given the reported propagation distance and increase in the use of ultrasonic antifouling systems, there is increasing concern over potential impacts of these devices. In 2022, Trickey et al. reported behavioral changes by goose-beaked whales in the vicinity of the ultrasonic antifouling systems. Further studies are needed to determine the risk to marine life due to these systems (Martin et al., 2023). In addition, a trade-off analysis of whether the impacts of sound from these systems may have a greater impact on the environment than the leachates is needed (Martin et al., 2023).

Resources

  • Guo, Shifeng & Lee, Hp & Khoo, Boo. (2011). Inhibitory effect of ultrasound on barnacle ( Amphibalanus amphitrite) cyprid settlement. Journal of Experimental Marine Biology and Ecology – J EXP MAR BIOL ECOL. 409. 10.1016/j.jembe.2011.09.006. https://doi.org/10.1016/j.jembe.2011.09.006
  • Lee, Tae & Nakano, Kazunori & Matsumura, Masatoshi. (2000). A New Method for the Rapid Evaluation of Gas Vacuoles Regeneration and Viability of Cyanobacteria by Flow Cytometry. Biotechnology Letters. 22. 1833-1838. 10.1023/A:1005653124437.  https://doi.org/10.1023/A:1005653124437
  • Legg M, Yücel MK, Garcia de Carellan I, Kappatos V, Selcuk C, Gan TH (2015) Acoustic methods for biofouling control: a review. Ocean Eng 103:237–247. https://doi.org/10.1016/j.oceaneng. 2015.04.070
  • Martin, S.B., MacGillivray, A.O., Wood, J.D., Trounce, K.B., Tollit, D.J., Angadi, K. (2023). Sound Emissions from Ultrasonic Antifouling Equipment. In: Popper, A.N., Sisneros, J., Hawkins, A.D., Thomsen, F. (eds) The Effects of Noise on Aquatic Life. Springer, Cham. https://doi.org/10.1007/978-3-031-10417-6_102-1
  • Sound Emissions from Ultrasonic Antifouling Equipment. The Effects of Noise on Aquatic Life, https://doi.org/10.1007/978-3-031-10417-6_102-1
  • Trickey, J.S., Cárdenas-Hinojosa, G., Rojas-Bracho, L. et al. Ultrasonic antifouling devices negatively impact Cuvier’s beaked whales near Guadalupe Island, México. Commun Biol 5, 1005 (2022). https://doi.org/10.1038/s42003-022-03959-9
  • United States Environmental Protection Agency. Office of Transportation and Air Quality. EPA-420-F-23-016. June 2023. https://www.epa.gov/system/files/documents/2023-06/420f23016.pdf
  • Woods Hole Oceanographic Institute (1952), “The History and Prevention of Fouling”, Marine Fouling and its Prevention (PDF), United States department of the Navy, Bureau of Ships.
  • Zhang G, Zhang P, Liu H, Wang B (2006) Ultrasonic damages on cyanobacterial photosynthesis. Ultrason Sonochem 13(6):501–505. https://doi.org/10.1016/j.ultsonch.2005.11.001