Ultrasonic antifouling grows as ‘green’ option for vessel owners
by Susan Buchanan,
Introduction by Susan Buchanan
By using sound waves, ultrasonic antifouling can prevent the growth of algae, barnacles and slime on boat hulls and interiors, and can protect sea chests and box coolers as well. The technology has been employed internationally from Europe to Australia, Japan, Chile and the Caribbean, and implemented on commercial, military and recreational vessels. More recently, these systems have caught on with yacht owners in North America. Fouled, rough hulls can slow boats and increase fuel consumption, and antifouling paints — while effective — can release toxins when a vessel is in the water or when coatings are scraped off in dry dock. Usage of ultrasound has grown following the International Ultrasonic antifouling grows as ‘green’ option for vessel owners by Susan Buchanan Maritime Organization’s ban over a decade ago on organotin in bottom paints, and because of moves to limit copper as an antifouling agent. Ultrasonic systems don’t rely on chemicals that can harm fish and mammals or pollute the air, and they can reduce vessel liftouts for cleaning. The cleaning abilities of sound waves have been recognized since before World War II. Starting in the 1950s, sound waves were utilized for this purpose in the food, agriculture, electronics, medical, aircraft and auto industries. While ultrasound’s marine applications have been acknowledged for decades, usage by commercial vessel operators has only gained traction in the past 15 years. To install a system, transducers are trends & currents Courtesy U.S. Coast Guard www.professionalmariner.com 37 antifouling can keep weeds, barnacles and mussels away without hazardous chemicals, cathodes or paints, (and) with no expensive lift-outs, scraping, high-pressure cleaning or the subsequent disposal of poisonous wastewater.” Impressed current antifouling (ICAF) systems typically use a copper alloy rod to prevent fouling and an aluminum or ferrous alloy rod to reduce corrosion, along with a power unit. Introduced to the market in 2008, NRG Marine’s Sonihull systems produce multiple pulses of ultrasonic energy in a range of targeted frequencies. These pulses are transmitted through the material to which the mounted inside a vessel’s hull, or on other internal features, along with a control box. Onboard generators or shore sources power the equipment.
Susan’s interview with delta-sistems’ Chiel de Wit:
For commercial users, the most common application of ultrasonic antifouling is protecting sea chests, bucket strainers, box coolers, intakes and piping for dry plate cleaners, said Chiel de Wit of delta-distems BV in the Netherlands. “In smaller vessels, we can also protect the hull,” he said.
In January, delta-sistems acquired Shipsonic™, a Dutch firm that introduced it’s ultrasonic anti-fouling technology in 2006. Shipsonic’s systems use ultrasound to prevent algae and barnacle buildup below a ship’s waterline and on box coolers, ballast tanks, water tanks and fuel tanks.
“Our biggest customer sector is the offshore industry, especially in Norway,” de Wit said. “Offshore maintenance and supply vessels have lots of machinery on board, hence they need a lot of cooling capacity. They have lots of box coolers.”
Ultrasonic antifouling has three big advantages, de Wit said. “These systems are dry-installed and maintained, so there’s no need to dry dock the ship,” he said. “They are cheap compared with conventional copper-anode technology. And ultrasonic antifouling technology is green, with zero impact on the environment.”
De Wit said ultrasound’s use in various cleaning applications is widespread, but it remains limited in marine antifouling for two reasons: reliability and effectiveness. “We think we have the biggest, purely technical challenges under control, however,” he said. “We’re now able to produce systems that are robust in the harsh conditions of the commercial marine environment, while also putting out the high wattage needed for the transducers to be effective. These systems withstand high temperatures, such as in the engine room, and they withstand big temperature changes and constant vibrations.”
“Transducers typically have a peak power of 100 watts or more, and our biggest system is eight times 100 watts,” de Wit said. “That results in pretty high currents and temperatures in the system.”
All producers of ultrasonic anti-fouling systems continue to face a lack of consistency in the technology’s effectiveness, according to de Wit. Comparable applications in comparable environments still produce different results. “We’ve run tests on one ship, with two identical systems on two similar sea chests, mirrored starboard and port, with unacceptable and as-yet-unexplained differences in results,” he said.
Shipsonic™ is entering a partnership with the Royal Netherlands Institute for Sea Research (NIOZ) to design and implement a research program to tackle issues related to the technology’s effectiveness.
“Once we’re able to offer a 100-percent-reliable fouling solution, we feel the market will grow exponentially,” de Wit said. “Shipsonic is working toward a completely new take, in which we’re moving from selling hardware to implementing solutions. The research program with the NIOZ will be a cornerstone for realizing this vision.”
Meanwhile, the company is participating in an experiment in Norway to keep net cages clean for the salmon industry.
Read the article in Professional Mariner April 2017 (page 36 onwards)
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