The Beaufort number is a category that helps one to conceptualize wind and categorize it.
I make a habit of measuring wind speeds when I'm out sailing. I find it help me to know my sailing limits and the limits of my boat. When I began sailing I really had no way to conceive how hard the wind was blowing other then how it felt or how the water looked. I found myself being more fearful then I needed to be of a strong breeze. My first wind meter helped me overcome my unwanted insecurity of the wind.
I often would gauge the wind based in the look of the water, wave size, whitecaps and what not. The trouble with this method is that wave size largely depends on the depth of the body of water, the amount of boat chop and how steep the shore is near the beach. The waves in the ocean are much different than wave on a lake. I't much better to quantify wind, and lucky for us it has been done.
A 0 (Calm) Beaufort number indicates almost no wind with glassy water. Perfect for water skinning. On Utah Lake you need to get up early in the morning to experience this type of water.
1 (Light Air) indicates wind speed up to 4 miles per hour. This is when you see ripples form on the water.
2 (Light Breeze) indicates a wind speed of just below 7.5 miles per hour. One can see small wavelets with glassy crests.
3 (Gentle Breeze) 7.5 to 12 miles per hour and large wavelets are forming and crests of waves are beginning to break.
4 (Moderate Breeze) From 12.1 to 18.9 miles per hour of wind you will see small waves and white caps.
5 (Fresh Breeze) In wind blowing at 19 to 24.7 miles per hour one expects moderate waves that are well formed lots of white caps and some spray.
6 (Strong Breeze) At 24.8 to 31.6 miles per hour expect large waves, whitecaps, spray.
At this point you may consider heading in, wind over 30 MPH is not impossible to sail riding Hobie, but it is difficult and potentially dangerous.
7 (Moderate Gale) At 31.7 to 38.5 mph if you are on the ocean at this point you would see the sea heaping up and some spin drift. I've never been out on my Hobie at more than 30 mph.
8 (Fresh Gale) At 38.6 to 46.6 you see some high waves with crests in to spindrift and well marked streaks of foam.
9 (Strong Gale) At 46.7-53.9 you will see huge waves and rolling seas, dense spray and limited visibility due to sea spray.