Beaufort Scale

Beaufort No.	MPH	Knots	Wind Description	Effect of Wind on Sea	Effect of Wind on Boats 15 to 40 Ft.
Force 0	< 1	< 1	Calm	Sea smooth and glassy	Becalmed; no steerageway; sails slat.
Force 1	1-3	1-3	Light air	Ripples; surface is ruffled by wind; some smooth patches may remain	Sufficient way on for steering; sails take airfoil shape loosely
Force 2	4-7	4-6	Light breeze	Entire surface ruffled; small wavelets short but pronounced; crest glassy	Boat sails easy and begins to heel.
Force 3	8-12	7-10	Gentle breeze	Large wavelets; occasional white caps	Good Sailing.
Force 4	13-18	11-16	Moderate breeze	Small waves, becoming longer; about half the waves show whitecaps	Small boats shorten sail; large ones carry working sails; genoas.
Force 5	19-24	17-21	Fresh breeze	Moderate waves of a pronounced long form; most crests show whitecaps; some spray	Small boats, reefed main only; large boats shorten sail.
Force 6	25-31	22-27	Strong breeze	Large waves begin to form; whitecaps everywhere; foam and spray	Small boats return to port; larger craft double reef.
Force 7	32-38	28-33	Moderate gale	Sea heaps up; white foam from crests blows in streaks	Storm canvas
Force 8	39-46	34-40	Fresh gale	Moderately high waves; edges of crests spume; heavier streaks of foam	Bare poles; lie ahull or run off with great care.
Force 9	47-54	41-47	Strong gale	High waves; dense streaks of foam; spray may affect visibility	Lie to sea anchor or run off, streaming drogue.
Force 10	55-63	48-55	Whole gale	Very high waves with long overhanging crests; great foam patches; much spray	Lie to sea anchor.
Force 11	64-72	56-63	Storm	Exceptionally high waves; foam patches cover sea; wave crest blown into froth	Seek shelter if possible.
Force 12	73 +	64 +	Hurricane (Atlantic) Typhoon (Pacific)	Air filled with foam and spray; sea completely white with driving spray	Seek shelter if possible.