U.S. Patent 8,240,609 “System and Method for Reducing Viscous Force Between a Fluid and a Surface” invented by Parazzoli, Tanielian, and Greegor (three Boeing researchers), was issued on August 14, 2012. Boeing’s drag reduction patent may hold promise for reducing the drag of conventional cage type or ring type propeller guards.

Viscous drag (the fluid stirring up near the surface) is a significant component of the total drag of many aerodynamic and hydrofoil surfaces. Previous attempts by others have tried to keep the fluid away from the surface. Examples include the Russian Shkval high-speed supercavitating rocket propelled torpedo, Riblets, and the use of suction or a blowing force through pores in the surface.

Boeing’s approach is highly technical but the basics involve the use of a metamaterial (an artificial, manmade material) that generates a magnetic repulsive force between the surface and the fluid.

While Boeing is obviously targeting aviation applications, they specifically note the material could be bonded to a hydrofoil, a boat hull, or a propeller blade. It looks like Boeing is contemplating the use of nanomaterials, or more specifically nanorods for the metamaterial.

Some ways the repulsing forces might be generated include reversing the Casimir-Polder-Lifshitz force between the material and the fluid. Or the repulsion forces might be generated by reversing the van der Waals force between the material and the fluid.

While this technology may still be a ways off, it is certainly worth watching and might one day find widespread use in boating, and might be applied to reducing the drag of propeller guards.