Biofouling is an old problem for boats. Barnacles, algae and other organisms attach to the hull and submerged components, increasing the need for cleaning and maintenance and, depending on how severe the fouling is, also increasing the vessel’s hydrodynamic drag.

Removing this fouling requires periodic maintenance. Besides the cost of taking a boat out of the water, hull cleaning has to take environmental aspects into account, since biofouling is recognized as one of the ways invasive aquatic species are carried between regions.

From naval sonar to ultrasonic antifouling

The link between ultrasound and marine biofouling has been known for decades. As early as 1947, there were US Navy studies on corrosion and fouling in sonar equipment.

Later technical literature also records the observation, attributed to naval tests carried out from the 1950s onward, that areas near sonar transducers showed less fouling.

These observations led to research and a range of technologies that use ultrasonic energy to hinder biofilm formation and the settlement of organisms on submerged surfaces.

The project challenge

ECK took part in developing an electronic antifouling system for boats, where one of the main requirements was low power consumption, allowing continuous operation from the vessel’s own electrical system.

Another challenge was the nature of the application itself. The transducer does not work in isolation. Once installed, it becomes part of an assembly made up of the transducer, its mounting, the hull and the water. The mechanical and acoustic response of this assembly depends on many factors, and relying on a single fixed operating frequency is not ideal.

The multi-frequency solution

The solution developed by ECK uses a firmware-controlled power electronics module to drive ultrasonic transducers at multiple frequencies.

Instead of staying on a single frequency, the system steps through a table of predefined frequencies. This strategy excites different conditions of the transducer-hull assembly and reduces dependence on a single operating frequency.

It also makes it possible to explore the different frequency bands used in antifouling applications. Studies show that the effect on biofouling depends on the organism, the frequency, the acoustic intensity and the installation conditions. That is why using multiple frequencies is particularly interesting in this application.

Power electronics and control

One of the main engineering challenges was developing electronics able to properly drive the ultrasonic transducers from the power available on board.

The project involved power conversion, MOSFET drive, step-up transformers, controlled frequency generation and embedded firmware.

The electronics convert the energy available in the boat’s electrical system into the signals needed to drive the transducers at the frequencies set by the firmware. The result is a low-power solution designed to deliver ultrasonic energy to the hull continuously.

How ultrasound works against biofouling

The energy produced by the transducer is transferred to the structure and to the water in contact with the hull.

Depending on frequency, intensity and operating conditions, ultrasound can produce surface vibrations and acoustic phenomena, including cavitation, that interfere with biofilm formation and the settlement of fouling organisms.

The goal is not to mechanically remove an established layer of barnacles, but to continuously disrupt the conditions biofouling needs to develop. This makes the technology particularly attractive as a preventive system.

Less fouling, less maintenance

For the boat owner, reducing barnacle and algae growth means longer intervals between hull cleanings. This can mean fewer haul-outs, less scraping and painting and lower maintenance costs.

There is also an important environmental issue. Organisms attached to hulls can be carried over long distances and introduced into environments where they did not originally exist. Biofouling control is therefore also one of the tools used to reduce the spread of invasive species.

Engineering applied to the problem

The project brought together several of ECK’s competencies in a single development. More than simply generating ultrasound, the challenge was to develop low-power equipment able to work across different frequencies, suited to the specifics of an antifouling application.

See other electronic engineering projects developed by ECK.