Skin deep

Sharks are among the fastest animals in the sea, partly due to the texture of their skin. Minute structures in their scales form a series of shallow ridges, known as riblets, which extend along their bodies from nose to tail, reducing drag and allowing them to reach high speeds without expending much energy.

It is a trick that engineers have always been keen to copy and it has been used with some success on ships and racing yachts. Polymer films with a riblet-like texture can be bonded to the hull to reduce drag and increase the speed through the water.

However, as design techniques become more sophisticated with computational fluid dynamics optimising aerodynamic forms, it is becoming more difficult to use riblets in the design.

The riblet-textured films are fine for flat or convex surfaces but the designs produced by computerised optimisation tend to have far more complex shapes, unsuitable for bonding.

Attempts to create a riblet texture on the surface have not been successful — laser-patterning and milling techniques can create the right sort of surface but as soon as a paint or lacquer is applied, it has the effect of smoothing out the surface, destroying the carefully-created texture.