The most widely used wind speed and sea state scale used by mariners is Beaufort scale. It is developed in 1805 by Francis Beaufort. The scale is not an accurate measurement, but based on observations. Although wind speed and sea state usually coincide, this is not always the case. The scale describes sea state on the open water, not near the shore. Local conditions can be consideraby different then on the ocean or as stated by weather forecast.
Common factors sailors need to observe:
- In proteced waters such as bays or one the lee side of an island, the water can be nearly flat in even high winds. Generaly wave heights depends on the fecth, the area over which the wind is blowing.
- As the waves reach shallow waters, they become shorter and higher, thus much stepper.
- Shifting wind direction create irregular waves.
- Wind agains current creates very confused sea (chop).
- Beaufort scale does not account for gusts.
Weather forecast sometimes states wind speed in a more descriptive form for the folks not familiar with the scale. Thus 'light wind' means up to 3 Bf. 'Moderate winds' up to 5 Bf. Above that there are three levels of official warnings. 6 and 7 Bf calls for 'Strong Wind Warning' (formerly Small Craft Wind Warning). 'Gale Warning' is issued when predicted wind speed is 8 or 9 Bf, and 'Storm Warning' for winds force 10 and 11. Force 12 is a huricane.