Ever since mankind first set sail there has been a need to protect vessels against the natural onslaught of marine biofouling species. Over the centuries an array of solutions have been investigated with varying degrees of success, from cladding ships’ hulls with copper plate to coatings based on exotic chemical concoctions delivered as a lacquer or paint. Whatever the fouling control approach adopted, sailors knew that keeping their ships hulls smooth and free of biofouling was a desirable outcome to maintain good speed, manoeuvrability and efficiency.
Today, making vessels sail more efficiently is not only of major economic concern to the ship owners, but also a necessity from an environmental point of view. While shipping is the most economical and environmental mode of transport, ships consume 350 million tons of fuel per year, costing $90 billion and emitting 1 billion tons of CO2 – equivalent to the emissions of a country the size of Germany. Antifouling coatings also play a critical part in avoiding drag and minimizing fuel consumption; biofouling can slow down a vessel by as much as 40%. Without effective antifouling coatings, the industry would potentially have to spend an extra $35 billion per year on fuel, and the environment would have to absorb another 400 million tonnes of CO2 emissions.
AkzoNobel’s Marine Coatings business, with its well-known brand International® which was founded in 1881, has been at the forefront of coatings research for decades. In 1974, we began to scientifically measure the performance of the various antifouling technologies. Now, we have the largest antifouling performance database in the world with records on over 250,000 vessels, and more than 10 billion data points. This year we asked marine biologist Dr Jeremy C Thomason from scientific and technical consultancy Ecoteknica SCP to independently analyse this accumulated store of big data. We asked him: what is the best antifouling coating in the industry? Are marine coatings technologies becoming more effective in battling fouling and improving sustainability?
Secondly, we also checked real vessel data and asked ourselves the question: which fouling control coating – on average – saves most fuel?
Types of popular antifouling coatings technologies
There are three main types of antifouling technology: controlled depletion polymer (CDP), self-polishing copolymer (SPC) and foul release (FR) – what do these mean and how do they work?
The rosin-based CDP technology launched in 1960s is now the most basic antifouling coating in the industry. A CDP antifouling paint works just like a bar of soap. If you leave it in a pool of water it becomes soapy and slippery. Likewise, water migrates into the CDP paint film which in turn dissolves rosin and biocides, which leach into the sea. As insoluble stay behind in the leached layer, the dissolution rate continuously declines and the remaining coatings system becomes less predictable and effective.
As early as 1974, AkzoNobel launched the first generation of the so-called SPC antifouling, which over the decades has developed into the most widely used technology in the maritime industry. An SPC antifouling coating reacts with sea water to make it soluble. The result is thinner leached layers with excellent control of biocide release. Similar to CDP coatings, water migrates into the paint film and the surface reacts with sea water ions, becoming soluble. The surface then dissolves, meaning that not only are biocides released, but the entire film thickness progressively washes off – thus solving the shortcoming of a CDP system. There are three main self-polishing copolymer (SPC) technologies currently available: copper acrylate, zinc acrylate and silyl acrylate. Predictable polishing rates enable specifications to be tailored to the ship type and operational profile.
Both CDP and SPC antifoulings polish away from the hull of a vessel. The coatings are applied with an appropriate film thickness to last the entire dry docking cycle – usually five years. At every docking the shipowner must invest in a new antifouling coatings system. Given the average age of 20-25 years of a vessel a shipowner should budget for around four to five antifouling systems per ship.
In 1996 AkzoNobel launched a completely new family of “biocide-free” antifouling coatings called “foul-release” (FR). Popularly known as “silicone” coating, this technology creates a rubbery “non-stick” surface which provides a very smooth, slippery surface to which organisms have a difficulty attaching. Foul release coatings, like our Intersleek®, don’t polish (or leach) from the hull. If a vessel doesn’t suffer mechanical damage, the Intersleek antifouling will continue to perform indefinitely. Many vessels, such as the Norwegian Sun from Norwegian Cruise Lines (NCL), sail with the original Intersleek on her hull for more than 20 years.
Norwegian Sun coated with Intersleek at newbuild in 2001. After three drydock cycles, she still has the original Intersleek 700 coating on the hull which only needed some touch-ups.
Which antifouling coating performs best?
In 1974, some inspired scientists from AkzoNobel set up a database to collect information on the performance of the company’s antifouling coatings. This database, called Dataplan, grew into the world’s largest dataset on the performance of in-service antifouling coatings. Our researchers continuously use Dataplan to investigate whether an antifouling system is likely to be successful. First, we verify whether an antifouling stays intact and undamaged on the hull. Secondly, we check if the antifouling coating keeps the hull “clean” from fouling.
We asked external expert Dr Thomason to analyse our database again. The results, as shown in the infographic, are quite revealing.
- All current coating technologies perform better than the average tributyltin (TBT) coatings introduced during the mid-1970.
- Eco-friendly foul release antifouling and high performance SPC coatings offer – on average – outstanding performance.
- Slime-resistant, advanced foul release coatings have the highest probability of performance success of 94%; this is 24% better than the rosin-based CDP systems. The more than 1000 successful applications of Intersleek 1100SR are a clear testimony of this success.
Read more from Dr. Thomason in this blog post.
From predicting clean hulls to fuel efficiency
While Dataplan is an invaluable resource for AkzoNobel’s fouling control coating experts, it doesn’t tell the whole story. Ship owners want more insights regarding the relative economic and environmental benefits of the various antifouling coatings. And this needs to be compliant with the ISO 19030 standard which AkzoNobel helped to create. To bridge this gap, AkzoNobel has created new models for predicting the impact of fouling control coating choices on ship powering requirements and operational efficiency, incorporating several refinements over previous models.
The two key additions are firstly, models for how the total roughness of the vessel changes over a drydock cycle for each coating option in response to the ship’s operational profile; and secondly, models to correlate the total vessel roughness to total ship resistance and powering requirements. The key outputs of these new models include predictions of vessel powering requirements, fuel oil consumption and cost, greenhouse gas (GHG) emission predictions and cost benefit analysis over the drydock cycle for each potential fouling control coating choice.
We currently have the performance data of hundreds of vessels which confirm the accuracy of the new model. As shown in the infographic, we now have a good indication of the relative fuel efficiency of the various antifouling systems. The main findings are as follows:
- The relative performance of the antifouling systems is consistent with the findings of the Dataplan This is not surprising. After all, a coatings system which performs relatively better should also result in better fuel efficiency.
- Eco-friendly foul release antifouling and high performance SPC coatings offer –on average- outstanding performance as they prove to be 3-10% more fuel efficient compared to CDP.
- The slime-resistant, advanced foul release coatings show the highest level of fuel-efficiency of 6-12% compared to CDP.
Better advice to the shipping industry
The new models are already being used commercially by AkzoNobel through Intertrac Vision, which allows ship owners and operators to make informed decisions regarding fouling control coating selection from both an economic and environmental perspective. As ship owners share their data with us we can also provide feedback on the actual performance of the antifouling coatings. The graph below confirms the improvement of fuel efficiency of 20% after the application of Intersleek 1100SR.
Certain fouling control coatings may work well on specific vessel type and trading routes but, based on our “big data”, we can draw some general conclusions regarding the relative performance of the various technologies. First, whilst the expectations of shipowners and other stakeholders are continuously increasing, marine coatings manufacturers have actually been able to develop better coatings solutions – the latest advanced foul-release is six times less likely to fail compared to the “good old” tributyltin (TBT) coating popular in the 1980’s and 1990’s. Plus, the improvement in relative fuel efficiency can be over12%. This equals a similar reduction in greenhouse gas (GHG) emissions which is great news for the environment.
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