0. 0 Calm. Sea like a mirror
1. 1 - 3 Light Air. Ripples but without foam crests
2. 4 - 6 Light Breeze. Small wavelets. Crests do not break
3. 7 - 10 Gentle Breeze. Large wavelets. Perhaps scattered white horses
4. 11 - 16 Moderate Breeze. Small waves. Fairly frequent white horses.
5. 17 - 21 Fresh Breeze. Moderate waves, many white horses
6. 22 - 27 Strong Breeze. Large waves begin to form; white foam crests, probably spray
7. 28 - 33 Near Gale. Sea heaps up and white foam blown in streaks along the direction of the wind
8. 34 - 40 Gale. Moderately high waves, crests begin to break into spindrift
9. 41 - 47 Strong Gale. High waves. Dense foam along the direction of the wind. Crests of waves begin to roll over. Spray may affect visibility
10. 48 - 55 Storm. Very high waves with long overhanging crests. The surface of the sea takes a white appearance. The tumbling of the sea becomes heavy and shock like. Visibility affected
11. 56 - 63 Violent Storm. Exceptionally high waves. The sea is completely covered with long white patches of foam lying in the direction of the wind. Visibility affected
12. 64+ Hurricane. The air is filled with foam and spray. Sea completely white with driving spray. Visibility very seriously affected.
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Big rectangular flags start flying straight enough, catamarans start going upwind on one hull 7-10 knots. If you face the wind you can hear it calling you in your ears
1 white cap 10-12 knots
2 white caps not too close, flags are flying straight, 12-14 knots, some chop and small waves after a while
Many white caps but no spray from the waves or too much sand flying across the beach 14-20 knots, after a while you can get big waves
Foamy waves breaking everywhere, spray flying off the tips of the waves, a lot of sand flying in the air and across the beach, + 20 knots
With waves that are already formed by wind that didn't reach the spot and/or stronger wind it's more difficult to judge the wind speed.