Sharks have to swim to survive. Many other fish have a more streamlined shape - and yet sharks still manage to outrun them. The secret of the shark’s speed lies in its special skin structure which helps it to move efficiently through the water. Although we will probably never quite catch up with sharks, we humans can now go a little bit faster thanks to the shark’s design tip.
When you go swimming the water doesn’t pass smoothly over your body. Instead it curls away from your body and creates swirling eddies and whirlpools around you, which scientists call turbulence. This effect exerts a drag force on your body and is partly to blame for slowing you down as you swim. Shark skin reduces the drag effect and helps them speed through the water.
Fastskin
Speedo, the swimwear manufacturer, specialises in developing swimsuits that mimic sharkskin. And it is confident that the latest design, ‘Fastskin FS II’, will help the Speedo team to haul in the medals.
Speedo enlisted the help of Dr Oliver Crimmen, the fish curator from the Natural History Museum in London. Taking a close up look at some sharkskin under a microscope, the team noticed that sharkskin is covered in tiny ‘V’ shaped ridges, known as dermal denticles.
To understand the purpose of these little ridges, the Speedo team carried out experiments in a flume tank and used computer models to study the fluid flow. The scientists discovered that the dermal denticles help to control turbulence and keep water flowing past the shark’s body. They reduce the drag forces by helping to create a ‘turbulent boundary layer’; a thin layer of disturbed water that surrounds the shark as it swims along.
Predicted CFD oil flow lines on the body of a male elite swimmer coloured by local water dynamic pressure (red = high, yellow = medium, blue = low).
Speedo realised that the shark’s dermal denticles could provide the perfect solution to reduce drag forces around a human swimmer. “We can’t make people into faster swimmers by changing their shape, but we can alter the texture of their swimsuit,” says Dr Crimmen. The team set about making a swimsuit fabric that would mimic the texture of shark’s skin, using some of the latest technology.
CyberFX, a Hollywood special effects company, created virtual models of elite swimmers so scientists could examine water flow without having to leave their desk. Effectively they set up a virtual flume tank inside the computer.
Next they used both fibreglass mannequins and real swimmers to test out the fabric designs in a flume tank at Otago University in New Zealand. Measuring the drag forces at different points around the body and at different water speeds enabled the scientists to calculate the best size and shape of dermal denticle for a human swimmer.
In 2000 Speedo produced the first swimsuit that mimicked sharkskin, known as Fastskin. These all in one, full-body swimsuits soon became a sensation, with many professional swimmers adopting them.
Predicted CFD water flow streamlines around the body of a male elite swimmer coloured by local water static pressure (red = high, yellow = medium, blue = low)
Since its release many world records have been broken by swimmers wearing Fastskin. Now Speedo is hoping Fastskin FSII will help break yet more world records.
A more detailed examination of the shark’s skin revealed that the size, shape and roughness of the dermal denticles vary. “A shark has very rough denticles on its nose and smoother denticles further back on its body,” explains Dr Crimmen. The rougher denticles encourage large swirls of water around the shark’s nose, which help to shelter the rest of the shark’s body from the drag forces.
So Fastskin FSII uses different fabric textures across the body. There are two main fabric textures: Fastskin (rough) and Flexskin (smooth). The new swimsuit tries to minimise drag forces by the careful positioning of the rough and smooth fabric. Extra nobbles have been added to the chest and back of the swimsuit, to mimic the effect of the rough denticles around a shark’s nose.
Tests in the flume tank have shown that Fastskin FSII reduces drag by up to 4% more than the original Fastskin.
The position of the fabrics on the swimsuit can be varied to optimise water flow for different body shapes and swimming strokes. So the men’s front crawl suit has a different layout to the women’s butterfly suit. Speedo is confident that all of these factors will give Fastskin FSII wearers the extra edge.
Meanwhile, Speedo continues to push the boundaries and is now working on an even more efficient swimsuit. What will be next? A shark fin perhaps?
For further information on the latest swimsuit technology visit: www.speedo.com
