Reducing the scale of drag

A coating for the hulls of ships that mimics sharks’ scales could prevent fouling by algae and barnacles without causing pollution, its developers claim.

When organisms attach themselves to ships, drag increases, reducing fuel efficiency. Conventional coatings can prevent this but leach poisonous copper into the ocean. This accumulates in harbours, threatening marine life. Researchers at the University of Florida have created an alternative coating composed of tiny scale-like elements.

The project is sponsored by the US Navy, which estimates that it could save up to £25m per year in fuel by reducing fouling-related drag. Full-scale ocean tests will begin later this month, and researchers at Birmingham University and an Australian team are also providing support.

Project leader Anthony Brennan, professor of materials science and engineering, realised that sharks remain free of barnacles and algae despite spending their lives submerged.

Sharks have placoid scales, consisting of a rectangular base embedded in the skin with tiny spines that poke upwards from the surface, making them feel rough. He mimicked this by creating a plastic and rubber composite coating made from billions of raised diamond-shaped patterns, each measuring 15 microns. Each diamond also contains seven raised ribs.