Is Hull Fouling as Harmful as Untreated Ballast?

At a presentation at the World Ocean Council's Sustainable Ocean Summit last month, IMO technical officer Dr. Theofanis Karayannis suggested that hull biofouling could be just as serious a problem for the spread of invasive aquatic species (IAS) as ballast water. IMO has adopted stringent standards for ballast water treatment, but at present it does not require measures for the management of biofouling. 

Dr. Karayannis highlighted research in several regions that found that biofouling was the primary vector for invasives. In New Zealand, fouling was found to be responsible for about 70 percent of IAS, compared to just three percent from ballast water. In Port Phillip Bay, Australia, about 80 percent of IAS reported was from ships’ hulls, with 20 percent from ballast water. In American waters, hull biofouling accounted for about 35 percent of IAS compared to 20 percent from ballast. He notes, though, that this pattern is not necessarily universal, and that there may be other examples showing that ballast water is the most problematic vector. 

Dr. Karayannis is not the first to raise concerns about hull biofouling. Australia has already enacted strict regulations on hull cleanliness, and researchers in many nations have begun to explore the connection between fouling and the marine environment. "Previously, the focus has been on ballast water," said Susan Williams, a professor of evolution and ecology at UC-Davis, in a 2013 interview. "Right now we really need to shift that management focus onto biofouling and hulls, which have been ignored. It is still necessary to manage ballast water, but there is a great need to begin addressing biofouling too."

More than 100 square miles of hull surface area arrives in the U.S. every year from overseas, and just one highly-fouled vessel can carry up to 90 tons of growth – including undesirable invasives like the green crab, the zebra mussel, the European fan worm, the Northern Pacific sea star and a variety of seaweeds, sponges, sea squirts and tunicates. 

In addition to the importance of managing this threat, Williams pointed out the obvious: shipowners have an economic incentive (up to a point) to reduce fuel consumption caused by biofouling. "It is very costly to have a dirty hull," Williams said. "And as the oceans have warmed, the species are growing bigger and faster, so there is a strong economic incentive to control hull species growth."

Hard coatings manufacturer Subsea Industries chalks up part of the problem to the end of tributyltin. "Antifouling systems in use since the ban on tributyltin (TBT) are less effective in eliminating hull fouling,” says Subsea chairman Boud Van Rompay. “Some species have developed a resistance to copper biocides and are thriving in ports and harbors where copper and organotin residues are high.”

Van Rompay asserts that a hard, cleanable coating is the only way to make sure that species do not get transported: if the hull is scrubbed before every departure, the hull is clean on every arrival. "The only real answer to preventing the spread of IAS is by ensuring that ships sail with a clean hull from their point of origin. Only a non-toxic hard-type coating and regular in-water cleaning can achieve this," he says. 

For shipowners interested in voluntarily reducing hull biofouling, there are several products on the market that claim a high level of anti-fouling performance and significant fuel consumption savings. Among the more novel options, AkzoNobel offers a non-toxic coating based on lanolin, a waxy byproduct of wool production, which offers up to six percent less fuel consumption. Hempel makes an advanced silicone hydrogel paint offering comparable performance, and it comes with a full satisfaction guarantee: if the owner doesn't like it, Hempel will remove it at the next docking.