Guest Editorial: Are Antifoulants Effective?

By MarEx 2013-05-28 10:54:00

By Mike Garside

Fuel costs are an ever-increasing problem. Pressure to reduce costs has brought us not only slow-steaming but now ultra-slow-steaming – all in an attempt to reduce voyage costs. 

The choice of hull coatings is one area which still presents a possible gain in terms of efficiency. But where there was once a comfortable certainty in the days of tributyltin (TBT) antifouling, there is now confusion. Even the measurement methods to determine the best coatings are an area of conflicting claims and counter-claims by paint manufacturers.

It is five years since the TBT ban came fully into force, and most ships have had at least one drydocking with newer coatings. Operators have had the chance to study drydock reports. In many cases the reports were not good news.

It is generally accepted that fouling can add from 5% to 40% to fuel consumption (one U.S. Navy study even puts the figure as high as 85%). Significant fouling can develop within days while sitting in port or even while steaming.  Even light slime adds significantly to fluid resistance. At 300 tons of fuel per day on a large cargo ship at a cost of around $180,000, hull coating efficiency is more important than ever.

The Golden Age of TBT

Operators may look back to the pre-2008 TBT days, when antifouling coatings were vigorous and long-lasting, as a golden era. TBT was the standard for over 40 years and was so effective that ship designers were even able to reduce engine size. The international ban ended that, and the true cost of TBT is only now becoming apparent: Ports such as Rotterdam dare not even carry out dredging operations for fear of stirring up the poisons from TBT antifouling which lie accumulated within harbor sediment.

Ship operators are still waiting for a successor. Many consider modern antifouling paints both ineffective and fragile. Long-term paint degradation (LPD), including blistering, delaminating, cracking and roughness from partial reapplication, afflicts most current coatings, and the copper-based biocides which replaced TBT simply don’t keep hulls clean as TBT used to. Since any biocide as effective as TBT at killing fouling is likely to face major regulatory barriers, it is a continuing problem.

Soft, Hard, or Slippery?

There are three main types of hull coatings on the market competing for business: (1) antifoulings (AFCs), containing substitute biocides, have the bulk of the market, followed by (2) superslick silicone or fluoropolymer foul-release coatings (FRCs), and (3) hard coatings with glass-flake technology, which are tough enough to allow frequent underwater cleaning. (Hard coatings are, crucially, the only type permitted to be cleaned in-water in most ports).

Paint manufacturers are now competing on measurement systems to support efficiency claims. Efforts to compare the effectiveness of coatings are fiendishly difficult, and there is no accepted standard. Frictional resistance to water is only one parameter among many: Efficacy is affected by ship design, engine efficiency, fuel quality, speed of sailing, draft, trim and list of the vessel, propeller design and condition, as well as ambient factors such as wind, waves, swell, currents, water depth, water temperature and salinity.

Measurements during non-steady conditions, such as while steering or changing speed, affect basic measurements. And LPD occurs over time, and hulls suffer minor damage from abrasions and are then painted over, resulting in unevenness.

AFCs and even many of the silicone/fluoropolymer coatings on the market contain currently-permitted biocides, usually based on copper or zinc. “Booster” biocides include agents such as the herbicide Diuron, the algicide Irgarol and, more recently, analgaesic and anti-inflammatory compounds. Even some of the manufacturers, however, privately accept that future legislation is likely to add these to the banned list. If that is the case, the days of antifouling may be coming to an end.

Maersk was an early adopter of silicone coatings and heralded them as a green move away from biocidal antifouling. But their later reversion back to copper-based AFCs was a massive blow to the reputation of silicone technology. Although little was said about the reasons for the move, there are indications that fragility and poor performance figures were factors. The costs of the reversion must certainly have been massive. The green credentials of silicone coatings were also damaged by studies which suggest that the oils in silicone coatings interfere with the development of fish embryos.

Underwater Cleaning

Hard coating manufacturers feel the way forward is to adopt completely inert coatings and to deal with the problem of fouling in a different way altogether. Hard coatings don’t attempt to prevent or lose fouling, but are designed to be strong enough to withstand regular cleaning. Each cleaning returns the hull to as-new condition. An added benefit is that hard coatings would be expected to last for the lifetime of the ship, requiring only minor touch-ups in a normal scheduled drydocking.

Any captain will agree that a freshly cleaned hull gives the best possible performance. But environmental concerns rule this out for all except the hard glass-flake coatings, which in practice require about 6-10 hours for underwater cleaning. Disney Cruise Line recently adopted this approach and is happy with the result. Its Vice President of Ship Engineering Frank de Heer says, “We tried it on the Disney Magic and were pleasantly surprised with the fuel savings. It’s a 20-year product that does not need to be reapplied.”


Legislative pressures, green pressures, and overwhelming financial pressures are all stacking up. While the coatings industry is currently estimated to be worth over $5 billion annually, coating costs are a pinprick compared to fuel costs. So the search continues. – MarEx

Mike Garside is a freelance maritime writer.