The Douglas scale is a scale used to classify the sea state at sea. It consists of two sub-scales from one to nine. Both partial scales assign a value to the swell (consisting of swell and wind sea ) and the swell separately. Waves that are generated under the direct influence of local winds on the surface of the water are referred to as wind seas. Swells are waves that do not come from current, local events.
The scale was conceived in the 1920s by the then captain and hydrograph of the Royal Navy , Sir Henry Percy Douglas , and adopted for international use in Copenhagen in 1929 . A similar classification system for wind strength is the Beaufort scale .
