Beaufort Scale

Francis Beaufort, of the British Royal Navy, devised his scale of wind force in 1805, when serving aboard HMS Woolwich, and first mentioned it in his private log on 13 January 1806. Accounts from 1704 show that a similar scale was in use a century earlier and it would be surprising if medieval Arab seafarers and the mariners of ancient times didn't use such a scale.

The Royal Navy adopted the Beaufort Scale in 1838 when it became mandatory for all ships log entries. Beaufort's scale of wind force assumed its present form around 1960, when probable wave heights and probable maximum wave heights were added.

Beaufort force	Description	Effects on land	Wind speed			Type of kite suitable
			knots	km/hr	mph
0	Calm	Smoke rises vertically.	Less than 1
1	Light air	Wind direction shown by smoke drift but not strong enough to turn wind vanes.	1–3	1-6	1-3	Only the lightest small kites with maximum lift.
2	Light breeze	Wind felt on face. Leaves rustle. Wind vanes respond to wind.	4–6	7-11	4–7	Lightweight small and medium sized kites.
3	Gentle breeze	Leaves and small twigs in constant motion. Wind extends light flags.	7–10	12-19	8–12	Perfect for most kites except very heavy ones
4	Moderate breeze	Raises dust and paper. Moves small branches.	11-15	20-29	13-18	Medium and large kites. Best for box kites.
5	Fresh breeze	Small trees begin to sway.	16-21	30-39	19-24	Strong, sturdy kites with good stability
6	Strong breeze	Large branches in motion. Telegraph wires hum. Umbrellas difficult.	22-27	40-50	25-31	Very strong kites only
7	Near gale	Whole trees in motion. Effort needed to walk against the wind.	28-33	51-62	32-38	Not suitable for kite flying