Since humanity first took to boats, we've fought twin battles against drag and fouling, seeking ways to make craft slip easily through water without unwanted passengers like barnacles. Inspired by carnivorous plants, Dr Chiara Neto of Sydney University has come up with a new solution, and seen it pass its first real-world test. The product could save money and help the environment.
Most of the energy required to move a ship is to overcome friction with the air and water, so anything that slips through the water easily is a boon. Unfortunately, fouling with barnacles, algae, or even bacteria increases friction, or drag, slowing journeys down and increasing fuel requirements.
Neto has designed a coating incorporating nanoscale structures that hold a layer of lubricant. Neto told IFLScience these structures reduce drag when fresh, and she is working on a paper quantifying the size of this benefit. In the meantime, she has published in Applied Materials & Interfaces a study demonstrating what is likely to be an even more important benefit in preventing bacteria taking hold on an underwater surface.
Bacteria induce little drag on their own, but the biofilms they form can help larger organisms grip ships' underbellies. The cost of fouling in Australia alone is estimated at US $250 million a year, and globally runs to many billions. The banning of the anti-fouling agent tributyltin for its disastrous effects on the wider marine environment has left ships exposed.
Neto shrink-wrapped materials with her nanostructure, in a process she compares to wrapping in saran wrap, or cling film, and infused them with non-toxic silicon oil. Having remained biofilm-free in the lab, Neto tied items treated this way to shark nets in Watson's Bay, off Sydney. After seven weeks the coated materials were unfouled, while comparison Teflon samples were entirely covered in marine life. Although the lubricant would need to be replaced eventually, Neto told IFLScience she is working on several methods for doing this cheaply.
Neto told IFLScience the idea was inspired by the Nepenthes pitcher plant, which traps a layer of water in its microscopic structures, causing insects to lose their footing and slide inside. The phenomenon has been copied by many scientists, but Neto decided to scale it down until even bacteria cannot grip.
Shipping currently produces only 2-3 percent of the world's greenhouse gasses. However, with solar and wind starting to reduce electricity emissions, and electric cars following fast behind, attention will soon turn to smaller, but harder to prevent, sources of pollution. Shipping appears among the most difficult industries to make carbon-neutral, but Neto's work might offer the opportunity to put a dent in its contribution.
So far, however, Neto's team lack a commercial partner to take the idea from an impressive prototype to a practical application.