Most antifouling paints are tested in stagnant water. A new pre-study within the Swedish Transport Administration’s industry program Sustainable Shipping shows that such tests provide an incomplete picture of how the paints actually perform under real conditions.

Marine growth, known as biofouling, is a well-known problem for shipping. Algae, bacteria, and larger organisms such as mussels and barnacles attach to ship hulls, increase fuel consumption, and drive up costs for shipping companies. Although it has long been known that biofouling is influenced by dynamic conditions (movement and water flow), few tests of antifouling paints have been conducted under such conditions.

“Dynamic testing is still relatively new, and the existing research is fragmented. The studies are based on different methods,” says Lena Granhag at Chalmers University of Technology, who led the project Biofouling on Antifouling Coatings under Static and Dynamic Conditions.

In the project, the researchers reviewed the entire body of scientific literature on antifouling tests under dynamic conditions—that is, where painted surfaces are exposed to flowing water. The analysis shows that dynamic testing primarily affects the formation of the so-called slime layer, the earliest form of fouling. This layer consists of bacteria, microalgae, and larval stages of larger organisms embedded in a sticky matrix of extracellular polymeric substances (EPS).

“A layer forms that resembles a natural surface, rich in nutrients, which attracts other organisms to glue themselves on. In addition, the slime layer also increases friction and fuel consumption.”

So how do paint manufacturers view this? They do conduct dynamic testing, but so far mainly from the perspective of paint durability, says Lena Granhag.

“But they are also very interested in dynamic testing from the perspective of antifouling performance. So this is a good moment right now. There is a shared understanding among European researchers and paint manufacturers. Even though manufacturers do not disclose their methods, the challenges can be discussed conceptually.”

And they are being discussed. This year, the French research platform GDR Biofouling & Environment was established, involving research teams and paint manufacturers from several countries. There is now broad agreement that standardized dynamic test methods are necessary to enable comparisons of results and to develop more effective and environmentally adapted antifouling solutions.

“It is important to test dynamically. Our analyses also show that plants and animals that grow in dynamic conditions—as they do on ship hulls—become more resilient and attach themselves more firmly and densely. The fouling therefore becomes more compact,” says Lena Granhag.

The pre-study Biofouling on Antifouling Coatings under Static and Dynamic Conditions was authored by Lena Granhag (Chalmers University of Technology), Youngrong Kim (Nanyang Technological University, Singapore), Emilie Adouane (Chalmers), Erik Ytreberg (IVL Swedish Environmental Research Institute), and Michael Leer-Andersen (RISE).