Jamie has found an excellent video on YouTube about Sea States: www.youtube.com/watch?v=JYQvymhZ2SQ.
As Hugh said Sea States are used in the Open Sea not inshore, where we tend to go. A lot of the video was shot around St Kilda, which is just about as “Open Ocean” as we will normally get. Here you get sea states 3 and 4 without the howling gales (” strong breezes”) that are necessary inshore to generate big waves. I am sure it does not help much to know that last Saturday the sea state was “slight”!