[math-fun] drag reduction via air bubbles

It has been found that by making your boat have a rough surface made of "ultra hydrophobic" substance, drag can be reduced versus a usual smooth surface. Air bubbles are trapped in valleys on the surface and so instead of water obeying usual "no slip condition" at solid surface, they contact an air bubble surface instead. The air acts kind of like a lubricant between the boat and the water. Sounds like a very promising idea.