A new propeller created by the Ningbo Institute of Materials Technology and Engineering (NIMTE) coated with a skin mimicking that of a dolphin holds the promise of significantly reducing fuel consumption and emissions in large cargo ships.
For over a century, scientists and engineers have looked at the dolphin as a model for building fast, maneuverable watercraft. After all, when you have an animal that can slip so easily through the water and leap into the air as if it doesn't care which medium it's in, it's a pretty good target for imitation.
The problem is that a dolphin shouldn't be able to swim like that. The drag is too much and a dolphin's muscles are pound for pound about as strong as a human athlete, so the animal shouldn't be able to reach the speeds it does. Up until the Second World War, this was a famous paradox, known as 'Gray's Paradox.'
Then engineers started to notice things. For example, if you watch seals and dolphins swimming together in a phosphorescent night sea, the lit plankton motes move around the seals in turbulent chaos, while they slide over the dolphins in straight lines. The culprit is the dolphin's remarkable skin.
Put simply, dolphin skin has a flexible microstructure that, combined with mucus excretions, is able to alter itself as Flipper swims at different speeds. At high speeds, the skin generates a very thin layer of turbulence. This layer is almost frictionless, allowing the water around the dolphin to simply slide over in what is called laminar flow.
Today, laminar flow is used in both watercraft and aircraft as a means of reducing drag and increasing speed. Now, NIMTE is applying the principle to ship propellers. Its "bionic dolphin skin" is applied to a conventional propeller and isn't exactly like that of a dolphin, which is much more complex. Instead, the coating is made of liquid-like dynamic interfacial materials and a flexible microstructure measuring between 0.1 and 0.2 mm. This reduces shear force with the water and improves propeller efficiency.
Working with COSCO SHIPPING Energy Transportation, NIMTE carried out tests of the bionic skin propellers on a very large crude carrier (VLCC) with a tonnage of 300,000 tonnes.
In test voyages over 200 days covering over 35,000 nautical miles (40,000 miles, 65,000 km) between Chinese coastal ports and major Middle Eastern ports, the propellers produced a 2% savings in fuel consumption for the crude carrier. The researchers estimate it would cost US$20,000 to place the bionic dolphin skin over a propeller, which would deliver cost savings of over $140,000 a year while cutting CO2 emissions by more than 900 tonnes.
Source: NIMTE
