Knot (unit) fluids (tidal streams, river currents and wind speeds) are also measured in knots. Thus, speed over the ground (SOG) (ground speed (GS) in aircraft) and rate of progress towards a distant point ("velocity made good", VMG) are also given in knots. Until the mid-19th century, vessel speed at sea was measured using a chip log. This consisted of a wooden panel, attached by line to a reel, and weighted on one edge to float perpendicularly to the water surface and thus present substantial resistance to the water moving around it. The chip log was cast over the stern of the
Wind turbine design from the blades' trailing edges and tips vary by the 5th power of blade speed, a small increase in tip speed can make a large difference. Wind turbines developed over the last 50 years have almost universally used either two or three blades. However, there are patents that present designs with additional blades, such as Chan Shin's Multi-unit rotor blade system integrated wind turbine. Aerodynamic efficiency increases with number of blades but with diminishing return. Increasing the number of blades from one to two yields a six percent increase in aerodynamic efficiency, whereas increasing the blade count from two to