Wave height and period as functions of wind speed, duration and fetch. The diagram allows the estimation of wave build-up to a fully developed sea. The white and green dots give two examples:1.) The series of white dots shows, from left to right: A wind of 30 knots produces waves of 2 m wave height with a period of 5.2 seconds after it has blown for 5 hours over a minimum fetch of about 35 nautical miles.
2.) Alternatively, the series of green dots shows, from left to right: A wind of 30 knots that blew over a distance of 50 nautical miles produdes waves of 2.6 m wave height with a period of 6.1 seconds, provided it blew for at least 6.5 hours. If it blew over a distance of 100 nautical miles the generated waves are 4.2 m in wave height and 8 seconds in period, provided the wind blew for at least 11 hours. Over a fetch of 200 nautical miles the same wind generates waves of 7 m wave height and a period of 12 seconds, provided it blew for at least 18 hours.
The fully developed sea from a 30 knot wind is reached at the blue dot (the end of the blue line), when the wind blew for at least 22 hours over a fetch of at least 350 nautical miles. It is characterized by waves of 8 m wave height with a period of 18 seconds.
(1 knot = 1 nautical mile per hour or approximately 1.8 km/hr)