An empirical scale from 0 to 12 that relates wind speed to observed sea surface conditions and wave heights.
In practice
For a watchkeeping officer, the Beaufort Scale is a practical tool for describing and recording weather conditions in the deck log, in weather reports submitted to meteorological authorities, and in communications with the master. Knowing that Force 8 corresponds to gale-force winds with wave heights of approximately four to five and a half metres allows an officer to communicate the severity of conditions concisely. The scale also calibrates seamanship expectations: heavy-weather procedures, securing of deck cargo, and reduction of speed are all tied to reaching certain Beaufort numbers.
Regulatory detail & full definition
The Beaufort Scale is an empirical wind-force scale ranging from 0 (calm) to 12 (hurricane force), defined by Admiral Sir Francis Beaufort in 1805 and formally adopted for international use by the early twentieth century. Each number corresponds to a range of wind speeds at a standard anemometer height of ten metres above the surface, and to observable sea state characteristics — wave height, foam, spray — that allow an experienced observer to estimate wind force without instruments. ICAO Annex 3 and WMO guidance support its continued use in marine meteorological reporting.
For a watchkeeping officer, the Beaufort Scale is a practical tool for describing and recording weather conditions in the deck log, in weather reports submitted to meteorological authorities, and in communications with the master. Knowing that Force 8 corresponds to gale-force winds with wave heights of approximately four to five and a half metres allows an officer to communicate the severity of conditions concisely. The scale also calibrates seamanship expectations: heavy-weather procedures, securing of deck cargo, and reduction of speed are all tied to reaching certain Beaufort numbers.
The Beaufort Scale underpins SOLAS requirements for voyage planning under Chapter V, which requires masters to take weather into account when planning and conducting a passage. Charter parties may include speed warranty provisions that excuse underperformance at wind forces above a specified Beaufort number. Accurate and consistent use of the scale in the ship's log creates a contemporaneous record of the weather the vessel encountered, which is valuable evidence in disputes over cargo damage or seaworthiness.