Fish scale the surface, interacting only with the riblet tips, not causing any high-veloctiy flow in the valleys. Since this high velocity flow now only interacts with the riblet-tip, which is a very small surface area, the momentum transfer which causes drag is now much lower than before, thereby effectively reducing drag. Also, this reduces the cross-stream velocity fluctuations, which aids in momentum transfer too. The rough, sandpaper-like texture of shark and ray skin, coupled with its toughness, has led it to be valued as a source of rawhide leather, called shagreen. One of the many historical applications of shark shagreen was
Chamois leather skin is soaked in clean fuel and placed over the grid in the funnel and brought up the sides, forming a bowl, to prevent any leakage past the skin. Fuel can then be pumped into the top of the funnel by the fuel dispenser and watched for signs of water accumulation. The process can be stopped to lift out the assembly from the tank and the trapped water removed so that the job can be continued. Chamois leather is used thus as a fuel filter by boaters, auto detailers—and aircraft refuellers, particularly of a past age when aircraft were flown