Whilst the subjects of polluting emissions from burning fossil fuels and introducing alien invasive species may seem unconnected, there is one area where the two come together. That conjunction is in the biofouling that ships can carry on their hulls. Biofouling is the main vector for species transfer and also inhibits the ship’s movement through the water meaning more fuel is needed to maintain the same speed.

None of this is new of course and ships are generally cleaned of biofouling at the two scheduled drydockings in the five-year cycle of special surveys. Biofouling is kept at bay using one of the anti-fouling or foul release coatings offered by coatings manufacturers. The premium anti-fouling products today are developed with specific vessel types and operational profiles in mind. They are long-life products and when chosen to suit a particular vessel’s needs can deliver fuel savings in the region of 7-14%. Over time, the build-up of biofouling will inevitably slow the vessel but here again, premium products can keep this speed loss down to a verifiable 1.0%.

Changing regulations

Many industry stakeholders argue the point that it is surprising that the IMO has never actually regulated the amount of fouling permitted given that the subject is so closely linked to the coatings used and these have been regulated by the 2001 Anti-Fouling Systems Convention. Furthermore, it is accepted that biofouling rather than ballast water is the main vector for invasive species and yet the IMO chose to target ballast water first.

Concerned by the lack of action states such as Australia, New Zealand and others have introduced their own legislation banning ships that are heavily fouled from entering ports. A small number of vessels have already been forced to leave ports and carry out removal of the fouling before being allowed to discharge cargoes.

To its credit, the IMO is currently exploring the possibility of introducing global rules covering biofouling through the GloFouling Partnerships Project established in 2018 by the IMO, the Global Environment Facility (GEF), the United Nations Development Programme (UNDP). This is the same route which resulted in the Ballast Water Treatment Convention.

Also, the IMO has produced voluntary guidelines on controlling biofouling by way of resolution MEPC 207(62) dating back to 2011. These guidelines are currently being revised with expectations that a first draft will be produced in time for PPR10 in April 2023 and MEPC 80 in June 2023.

For its part, the shipping industry itself is becoming concerned over the growing patchwork of regulations and policies globally which create a complex regulatory landscape for ship owners seeking to manage biofouling proactively.

Evolving hull cleaning practices

Cleaning the hull between drydockings is not unusual but older methods such as scraping the hull by divers and machines without collecting the residues addressed the efficiency issue, but probably worsened the environmental aspect by actually freeing organisms into the environment where the cleaning took place. Such aggressive cleaning could also damage the underlying anti-fouling coating making future fouling likely to occur quicker and be heavier.

Modern day cleaning practices are much more in tune with current thinking on protecting the environment. Instead of employing divers to inspect the hull when biofouling is suspected, constant monitoring of vessel performance can signal when the accumulation of slime – the precursor to biofouling – has advanced to the point where it is impacting efficiency. Once identified a cleaning operation using divers or robotic equipment can be scheduled and carried out. And today’s cleaning tools often have a means of collecting the removed fouling allowing safe disposal ashore.

Benefits of early action

With the new proactive cleaning approach, biofouling is removed before it causes a measurable reduction in hull performance, there is a very low performance loss and corresponding to this there is a reduction in both carbon emissions and fuel cost. Biofouling is also removed before it reaches the macrofouling stage virtually eliminating the risk of transfer of invasive species.

In addition, the biofouling is removed before it has firmly attached to the hull surface and therefore before removing it results in a risk of damaging or eroding the hull coating and also a risk of contaminating the water column. In order to fall under the definition of proactive cleaning, however, the cleaning must be done at a sufficiently high frequency.

In a real-life study carried out by Jotun on a reactively cleaned vessel when fouling accumulation was advanced and removed only four times in a five-year period there was an accelerated drop in performance following each reactive cleaning. See below graph

The average over period speed loss was 6.2%. As compared to keeping the hull always clean by a high frequency of proactive hull cleanings, the excess fuel consumption and increase in carbon emissions was around 18.6%. Using a system such as Jotun’s HullSkater combined with a premium antifouling would likely have reduced extra fuel consumption to below 2% and the speed loss down to just 0.5%.

Commenting on the subject, Petter Korslund, Regulatory Affairs Manager for Jotun Performance Coatings said, “More and more ship operators are seeking ways to improve the efficiency of their vessels and arguably the lowest hanging fruit still left to them is the use of premier antifouling and proactive cleaning methods available today.

“Certainly, employing proactive cleaning techniques is beginning to be noticed by the bodies dealing with the issue. The recent GEF-UNDP-IMO GloFouling Partnerships Project and Global Industry Alliance (GIA) for Marine Biosafety report titled ‘Analysing the Impact of Marine Biofouling on the Energy Efficiency of Ships and the GHG Abatement Potential of Biofouling Management Measures’ includes reference to proactive cleaning as a means to help prevent biofouling,” points out Korslund.

Jotun is a member of the GIA and encourages the inclusion of proactive cleaning as part of the good biofouling management toolbox. The report from the GloFouling-GIA says proactive hull and propeller cleaning has the potential for economic and environmental benefits, not only because it can proactively eliminate the possible penalties of biofouling, but also it can save the cost associated with intensive hull cleaning in dry dock. Proactive cleaning is less aggressive and thus causes less damage to the anti-fouling coating, while reducing the risk of transporting invasive alien species.

Parallel to its work in the GIA, Jotun is also supporting the Clean Hull Initiative. Korslund explains, “To address both the increasing focus on biosecurity and ship efficiency, ideally the industry and regulators should between them develop a standard for proactive biofouling management. The first step to do this was taken at Nor-Shipping last year when environmental NGO Bellona Foundation officially launched its Clean Hull Initiative. The intention is that stakeholders such as regulators, operators, ports, coatings manufacturers, technology and service providers, as well as academic and research institutions will work towards developing an ISO standard for proactive hull cleaning.  Cross industry collaboration is key to making this happen.”