Controlling the hidden financial and environmental costs of biofouling

The following article is authored by Dr. Sasha Heriot, Product Development Business Manager, Cathelco. It takes you on a deep dive into the topic of marine biofouling and presents effective ways of reducing and combating this phenomenon.

Courtesy of Cathelco

Ship owners are under pressure to decarbonise. With alternative fuels in short supply, energy-saving technologies present immediate opportunities to save fuel, lower emissions and reduce costs. One often overlooked contributor to a ship’s fuel efficiency and total emissions is the impact of biofouling.

This hidden threat is the accumulation of aquatic organisms on submerged surfaces which reduces vessel efficiency, increases drag, decreases fuel efficiency, and raises operational costs.

The International Maritime Organization (IMO) recognises biofouling management as an effective tool for enhancing energy efficiency and reducing ship emissions.

Fortunately, measures to combat biofouling are continuously improving, and ultrasonic antifouling systems represent a transformative technology. Using sound waves, they provide a proactive, sustainable solution to keeping vessel hulls clean, reducing emissions and costs, and preventing the transfer of invasive species.

Biofouling impact

As soon as a vessel enters the water, it becomes susceptible to biofouling and host to a diverse ecosystem of marine life. It starts with organic molecules sticking to vessel surfaces, which attract microorganisms to feed on them, forming a biofilm.

At this point, macro-organisms like barnacles, mussels, and sponges feed on the biofilm and establish themselves. This creates a rough and uneven surface, increasing drag and impacting the vessel’s hydrodynamic performance.

Even micro-fouling creates friction, affecting vessel drag and performance. As drag increases, fuel consumption and emissions rise as engines work harder to overcome resistance. Consequently, efficiency drops, leading to higher operational costs for vessel owners, including soaring fuel expenses and shorter maintenance intervals.

The impacts of biofouling extend beyond the hull, affecting sea chests, bow thrusters, hull appendages and protrusions. Unchecked marine growth clogs seawater intake systems, reduces flow, and contributes to corrosion, jeopardising vessel integrity.

Regulatory compliance and environmental initiatives

The IMO acknowledges the significance of biofouling management in reducing emissions and achieving sustainability goals, citing it as a key optimisation element for its Carbon Intensity Calculator (CII). A study by the Global Industry Alliance for Marine Biosafety – part of IMO’s GloFouling Partnerships Project – shows that keeping hulls clean can reduce a ship’s GHG emissions by up to 25%, directly supporting the IMO’s net-zero emissions goal by 2050.

At the launch in December 2022, Dr. Jose Matheickal, Chief of Department of Partnerships and Projects at the IMO, encouraged the maritime industry to consider biofouling management as one of the easy ways to save GHG emissions.

Biofouling not only creates operational and emissions challenges but also ecological risks, facilitating the transfer of invasive aquatic species alongside ballast water. Detached organisms reproducing in non-native areas can wreak havoc on fragile ecosystems, outcompeting and endangering indigenous species and disrupting delicate marine habitats.

The spread of invasive species is recognised as a significant threat to both ecological and economic well-being of the planet and one of the main drivers of biodiversity loss. The IMO has implemented strict guidelines to prevent their spread, emphasising the importance of effective biofouling management in safeguarding marine biodiversity. Updated Biofouling Guidelines were adopted at MEPC 80 in July 2023, reflecting this commitment.

Evolution of biofouling management

Traditionally, vessel operators have relied on antifouling coatings plus periodic hull cleaning and propellor polishing to manage biofouling. However, these methods have limitations including environmental concerns, labour-intensive maintenance, and high costs.

Moreover, the reactive nature of manual cleaning, either underwater with robots and divers or during dry-docking, means biofouling is left to accumulate before action is taken, thereby accruing hidden costs.

Various proactive solutions exist to protect different vessel parts from biofouling. For example, marine growth prevention systems (MGPSs) like Cathelco’s use copper anodes installed at seawater intakes to deter marine organisms from settling. By preventing build-up or blockage in the pipework, MGPSs help avoid overheating and potential machinery shut-downs, accelerated corrosion, and reduced firefighting capability. MGPSs excel at addressing macro-fouling and are suited for volume treatment in areas like sea chests, internal pipework, and box coolers. In contrast, ultrasonic protection (USP) is more effective for early-stage prevention of micro-fouling and surface treatment.

Ultrasonic antifouling systems work alongside antifouling coatings to ensure the hull remains clean and smooth from the outset. Transducers are attached to the inside of the hull and emit ultrasonic waves, disrupting biological attachment. These waves penetrate the hull plate, disturbing microorganism cell membranes and preventing them from attaching. Simply put, it causes the surface to vibrate, which biofouling does not like, so it moves on rather than settling.

Harnessing the power of sound: the science behind ultrasonic antifouling

The EU-funded CLEANSHIP project, in collaboration with Brunel University and Lloyd’s Register, found that even six months without protection against marine fouling deposits can lead to increased drag on the hull so much so that a ship may use up to 40% more fuel and produce 40% more CO2 emissions.

It proposes a harmless and cost-effective solution for fouling prevention without the need for taking a ship out of service. The solution is the deployment of long-range ultrasonic plate waves travelling throughout an entire ship hull below the water line to both prevent and slow down the accumulation of fouling and achieve a continuous monitoring to allow earlier and cheaper removal.

Ultrasonic antifouling systems leverage established techniques such as guided wave and heterodyning to ensure superior protection against fouling organisms.

Guided wave, traditionally used in non-destructive testing, is an array of transducers of the same frequency, arranged in a certain way, which generates a guided wave effect and creates vibration on a surface.

USP technology enables the waves to travel over longer distances than traditional ultrasonic fouling solutions, which means up to 60% fewer transducers are required. This delivers lower installation and operational costs and makes the system more reliable and easier to manage, as there are less transducer locations, fewer cable runs, and fewer control panels.

Dr. Sasha Heriot, Product Development Business Manager at Cathelco. Courtesy of Cathelco

Heterodyning, also called frequency conversion and originally used in radio frequency tuning, generates multiple frequencies to target a wider spectrum of fouling organisms, ensuring comprehensive protection in diverse marine environments and seasons. Single frequency transducers are unable to protect against all species of fouling. Generating more frequencies enables protection against a broader range of fouling species, thereby enabling increased range and optimum efficiency.

DragGone applies these existing and established principles to this use case for the first time and has been tested and validated for efficiency and safety and is proven to deliver up to 13% improvement in fuel efficiency. It was piloted on a 78.5m car ferry operating between Denman Island and Buckley Bay on Vancouver Island. Before installation, the vessel experienced high drag levels, preventing it from achieving the required number of transits per day.

Financial and environmental sustainability in maritime operations

By targeting both micro- and macro-fouling, a combination of MGPS and ultrasonic protection technology offers a comprehensive approach to effective biofouling management for surface and volume treatment.

As the maritime industry strives to reduce its costs as well as its environmental footprint, aligning biofouling solutions with sustainability goals is increasingly important. Embracing innovative technologies like ultrasonic antifouling systems allows vessel operators to enhance operational and fuel efficiency while reducing drag and associated emissions.

These proactive solutions to the hidden costs of biofouling not only benefit the bottom line but also contribute to a cleaner, greener maritime ecosystem.


Disclaimer: The views and opinions expressed in this article are those of the author and do not necessarily reflect the official policy or position of Offshore Energy.