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Paint degradation hidden contributor to CO2 emissions

Degradation of anti-fouling paints, leaving a rough surface which increases water resistance, is often overlooked as a reason for deteriorating fuel efficiency in ships.

By and large, ship operators are more than happy to do what they can to lower CO2 emissions.

Fuel consumption is by far their largest operating cost, and fuel efficient ships burn less fuel. Paint manufacturers sell their paints on the basis of reducing frictional resistance from the water and keeping hulls free from marine growth – fouling.

But smooth and sleek hulls fresh from the dockyard don’t stay that way. Drydock visits after 5 or even 2.5 years, typically reveal badly deteriorated paintwork which  is patched up as quickly as possible. Mega-ship operator Maersk certainly keep a close eye on their fuel bills, and appear to operate a policy of aggressively cleaning ships in service and paying out for a comlpete re-paint every couple of years. Such a practise suggests little confidence in the life-cycles claimed for anti-fouling paints.

At least two studies by Dr. R.L. Townsin say that 40µ per year of added roughness is caused by degradation of regular anti-fouling paints. The cost of this added roughness is large, according to estimates by the Arab Academy for Science and Technology and Maritime Transport: each 10µ of added roughness reduces speed by 0.03 knots and increases fuel consumption by 1%. That adds up to a 16% fuel penalty after five years service.

Figures from anti-fouling manufacturer Jotun put the penalty of paint degradation even higher. Bjørn Wallentin, Jotun Coating’s global sales director for hull performance solutions, was quoted in Marine Propulsion 2011 as saying: “Blasting will change the hull condition from rough and possibly fouled, to smooth and clean. We know that this surface preparation can improve fuel consumption by about 25-40 per cent, depending on prior condition.”

There has been little published research into the precise speed of degradation of anti-fouling paints, or on precisely its effects. There is no doubt however that it is a significant added cause of CO2 emissions.


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