Ultrasonic antifouling works in two ways. First by preventing attachment of new fouling to the surface of the hull. The second function is the disruption of reproductive and life cycles of organisms attempting to populate the surface. It’s important to remember that an ultrasonic system will not reverse existing fouling – the effects of ultrasonic antifouling are preventative.
What is Marine Fouling
Fouling is the process of marine organisms attaching and growing on surfaces below the waterline. Underwater surfaces are coated with man-made substances that will inhibit this growth. Coatings may be combinations of toxic chemicals and self-polishing or ultra-slick surfaces. The purpose is of course to prevent marine organisms from attaching to your underwater surfaces.
Effects of Ultrasonic Stimulation
Ultrasounds are frequencies above that which can be heard or perceived by people. Ultrasound equipment is a large part of our daily lives and includes devices such vehicle parking sensors, ultrasound imaging in hospitals, and sonar on boats. Just as the frequency of light can produce a wide variety of phenomena such as radio, visible daylight, and microwaves, so the same is true for ultrasound – different frequencies will produce a diverse effects ranging from imaging, communication signals, and biological cellular disruption.
Different frequencies affect marine fouling in different ways. Ultrasounds between 20kHz and 40kHz produces a high pressure barrier along a surface. This microscopic barrier is only a few microns thick. Small organisms cannot occupy this high pressure space and are prevented from attaching to the surface.
Other frequencies have a different type of function. At frequencies above 40kHz, the cellular structure of fouling organisms that have attached to the surface begins to be effected. Common tasks related to organism life processes and reproduction cycles are disrupted within this frequency range.
Implementation of Ultrasonic Antifouling
Contrary to audible sound waves which can travel great distances through the air, ultrasound is most effectively transmitted through rigid surfaces. Consider ground penetrating radar – ultrasound can be utilized to create mapped images of depths over 100 feet through solid rock. Likewise, the ultrasound produced by Hull Shield systems must be past directly into the surfaces that are to be protected. To do so, emitters are bonded directly to the hull surface at evenly spaced intervals. These emitters are connected to a fully automatic control unit that generates signals within targeted frequency bands.