Sankey diagram (power)

A Sankey power diagram is a flow chart whose arrow widths are proportional to power, used to show where energy is lost between the engine and the water in a propulsion plant. It traces brake power at the engine flange to delivered power at the propeller (gearbox and shaft-bearing losses), then to thrust power and finally effective tow power, with the gaps representing the quasi-propulsive coefficient: hull, open-water propeller, and relative-rotative efficiencies. On a typical merchant ship only about 0.6 to 0.7 of brake power reaches the water as useful tow power. The diagram is a standard way to present the powering chain and target the largest losses.