Background

The efficiency of movement of a body through a fluid (liquids and gases) is improved by the smoothness of the external surfaces of the body. Conversely the presence and exposure of roughness, imperfections, gaps and steps on the external surfaces of the body impairs efficiency.

More specifically, the reduction in external surface-friction drag in boats, aircraft or any other structural body passing through a fluid is to maintain a condition called laminar flow, in which water or air slides smoothly over the surfaces of hulls, wings, blades or other external surfaces of a structure.

With regard to practical engineered structures fabricated from many components moving through a fluid, the typical presence of surface roughness, imperfections, joint fastener heads, surface waviness, gaps and steps leads to a transition from laminar flow to turbulent flow resulting in increased surface-friction drag and a loss in speed, power and efficiency.

Surface seals and fillers can be used to restore surface smoothness, but currently both suffer inherent limitations: the step size introduced by the thickness of seal, and the durability of filler with respect to the long term operating environment leading to sealant swelling/dishing/cracking (fluid pressure, surface temperature, surface strain matching compliance and in-service surface treatments).