In the decades-long battle for naval supremacy that was fought between Britain and France at the end of the 18th century, the British fleet had a secret weapon. It was, as secret weapons often are, hugely expensive. But it paid off, giving British ships more speed, manoeuvrability and staying power than their French rivals. It was copper.
By covering the underwater parts of their ships' hulls with copper plates—which slowly dissolved, releasing toxic copper ions as they did so—the British admirals stopped barnacles, mussels and burrowing clams from taking up residence. In fleets that were otherwise well-matched the result was decisive. France lost. The British empire became the global superpower of the 19th century. And the world speaks English, not French.
Ship-fouling, then, can have rather far-reaching consequences. Even now, when naval supremacy is less of an issue, the problem is rife. The drag imposed by a heavy infestation of barnacles may push a ship's fuel consumption up by as much as 40%. The solution usually adopted is similar to the Royal Navy's: poison. Copper is still used, though in the form of copper-laced paint. Another popular chemical is tri-butyl tin. But releasing toxic heavy metals into the sea is frowned upon these days—indeed, tri-butyl tin is now illegal in many parts of the world—so the search is on for alternatives.
One possibility is to use one of a group of chemicals called avermectins. These are antiparasite agents (the most familiar of which is called ivermectin) that are widely used against fleas and gut worms. They also, according to Hans Elwing of the University of Gothenburg, prevent barnacle colonies from taking hold by stunting their growth. A barnacle that runs into the chemical finds it cannot bind as strongly to the surface. Only a tiny amount, about one part in a thousand of the paint by weight, is needed, and other marine species are not, as far as can be ascertained, affected by it.
Another way to discourage barnacles is to confuse them. A formula developed by Giancarlo Galli of the University of Pisa uses polymer molecules that are water-attracting on one side and water-repellent on the other. When they are painted onto a surface, this arrangement forces them into a kind of checkerboard pattern which makes it much harder for barnacles and mussels to stick, according to David Williams, who is in charge of commercialising the idea at AkzoNobel, a multinational chemical company.
If checkerboarding does not work out, AkzoNobel has an alternative: create a surface so smooth that barnacles cannot hold on to it. This is done with a fluoropolymer—a chemical similar in structure to Teflon. The paint does not stop the animals attaching themselves to a hull in the first place, but once the vessel is moving faster than ten knots, the water sweeps them away. That is no problem for commercial vessels, which are always on the go. But for pleasure boats, which may spend a lot of time idle, Dr Williams's team is trying to improve the formula so that a boat need not be moving so fast before the paint does its job.
Small boats, particularly on inland waterways, are also the focus of work by John Schetz of the University of North Texas and Robert McMahon of the University of Texas. They have been experimenting with a mixture containing a molecule similar to capsaicin (the active ingredient of hot peppers) and another similar to THC (the active ingredient of cannabis). Fouling is less of a problem for boats in fresh water, as barnacles are purely marine. But recently the inland waterways, docks and fresh-water intakes of North America have been overrun by zebra and quagga mussels—species that originate from the area around the Black Sea. The mixture Dr Schetz and Dr McMahon have come up with seems particularly effective against these animals, though they have yet to commercialise it.
Their aim is not just to help boat owners, but also to stop them unwittingly spreading the mussels still further. According to Dr McMahon, a big part of the problem is that both species can survive out of the water for several days, so transporting a boat overland from one river basin to another, a common practice in North America, will not necessarily kill them. Also, boat owners are not always as diligent as they might be when it comes to inspecting their vessels for signs of infestation. And even if they do look, the mussels can be hard to see, especially when they are young and therefore small.
There is thus a lot to play for. Reducing fouling will save fuel, in turn saving money, as well as cutting shipping's contribution to greenhouse-gas emissions. And stopping the spread of invasive mussels will make life easier for those who navigate the waterways of America and Canada. The prize may not, this time round, be world domination. But whoever comes up with the winning formula is likely to make a fortune.
External link: http://www.economist.com/node/21527029#!