Clean hulls wins in the long run
To reduce fuel consumption and carbon dioxide emissions, the growth and settlement of fouling organisms must be controlled. At the same time, the antifouling paints used today leak toxic substances - actually more than the manufacturers state. This was found in a research project run by Lighthouse within the Swedish Transport Administration's industry program Sustainable Shipping.
Only the algae growth can increase fuel consumption by 10 percent, says Erik Ytreberg, a researcher at Chalmers. Of course, it’s not sustainable – neither environmentally nor economically.
"The challenge is to develop paints or hull cleaning techniques that are effective and also have a low environmental impact."
But how do you do that? There are many parameters to consider. For example, things that work in some waters and on some vessels do not work with others. It is difficult to develop a general method.
"Today there is the use of, for an example, smooth silicone paints. The disadvantage of them is that they only work at high speeds, often over 12 knots and also can't handle ice. The proportion of vessels that can use them is therefore not so great."
Chemically active colors are the ones most commonly used. They leak poison, especially copper, to keep away the growth. The problem is that they both leak too much and too little. Copper content in the Baltic Sea and Sweden's coastal waters is far too high.
"In some cases, we have been able to see that a color containing seven percent copper oxide is as effective as one containing 40 percent."
Another problem is the rate at which the colors release their poison. Some are very effective in the beginning, but stop working after a couple of years and therefore the hull must must get cleaned. Studies in the project have shown that it is common for many vessels to be cleaned continuously every 6 to 12 months.
"Although many try to do it correctly, there is a great risk that poison particles will end up in the sea."
Cooling, heat and saltiness also play a role in the efficiency of the colors, which means, for example, that Stockholm archipelago require different colors than Bohuslän. In the research project, led by Erik Ytreberg and colleague Lena Granhag at Chalmers, such data is analyzed and mapped.
"We will develop a tool that offers tailor made solutions which optimize color selection and hull cleaning systems so that fuel consumption, poison leakage and climate impact are kept as low as possible", Erik Ytreberg says.
The three year project, done together with SSPA and the University of Gothenburg, also involves shipping companies, authorities, ports, hull cleaners and paint manufacturers. So far, the effects of salts on colors and how much they leak have been studied.
"Our results indicate that the colors are leaking more than the industry reports to the authorities."
More articles on projects within Sustainable Shipping
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In search of keys to fossil free waterborne public transports
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