A team of students working with Jonathan Boreiko, an associate professor of mechanical engineering at Virginia Institute of Technology, discovered a method that ducks use to keep them completely wet while swimming.
When the duck comes out of the water, it is shaken with feathers and becomes dry. This means that water cannot reach the bottom of the porous structure of the feathers.
The team first needed to make sure that water can only penetrate directly through the feathers, and not just seep along their outer edges. To achieve this, the authors modeled one feather at a time, leaving only a small area open.
The researchers sealed each layer, backing the same distance between the feathers. Then they poured water onto the upper open surface. The stack was placed in a pressure chamber and gas pressure was used to push the water down through the feathers. A camera was installed at the bottom to observe the water passing through the layers.
The feathers have micro-sized holes and pressurized water flows through these tiny slits. A duck sitting on the surface of a pond does not experience any water pressure. However, when the bird dives down, they are faced with a constant increase in hydrostatic pressure, which is familiar to anyone who dives deep underwater.
The authors found that as the number of layers of feathers increases, the pressure required to push the water increases. This establishes a kind of baseline, the maximum pressure up to which the feathers hold the water entering them, but prevent the water from reaching the duck’s skin.
The authors also noticed that different types of ducks tend to have the exact number of layers of feathers needed to avoid getting completely wet while diving. For example, a mallard has four layers of feathers. The maximum depth to which a typical mallard dives corresponds to the hydrostatic pressure that its three layers can withstand. This way, at least one layer of feathers remains dry after submersion, allowing the duck to stay dry.
The synthetic feathers gave nearly identical results during testing. Also, scientists have plans to use the knowledge gained in the creation of water vehicles. For example, you can apply multi-layered synthetic feathers to the outside of your boat to make it easier to navigate the water.
