A knot is a unit of speed used in maritime references. In Table 4.5, wind speeds are listed in knots. The Beaufort scale starts with 0 and goes to a force of 12. Britain’s Admiral Sir Francis Beaufort created the Beaufort scale in 1805 to help sailors estimate the winds using visual observations. Table 4.5 describes the characteristics of the different sea states, including the official measure of wind strength as defined by the Beaufort scale, the wind speed, the wave height, and the visual characteristics of the sea as observed from both land and water. For example, sailors on the Great Lakes of North America, although not technically at sea, still refer to sea states. Sea state terminology is sometimes applied to sailing conditions in places that are not seas. Wave conditions at sea are called sea states. Swells formed in the Antarctic can travel all the way to Alaska. For example, swells from winter storms in Alaska supply the big waves surfed on the North Shore beaches in Hawai‘i. Once formed, swells may carry the energy of storms thousands of kilometers. Swells may be generated by prevailing winds, such as tradewinds, which blow over long fetches for long durations. They no longer need additional wind to push them onward. Swells are waves that have obtained enough energy to travel beyond their generation area or fetch. Seas are characterized by waves of differing heights coming from many directions (Fig.
Seas may include ripples, chop, wind waves, storm waves, and swells. Sea is a term used to describe the mixture of waves often observed from ships. The same is true of waves larger, faster waves have more energy and a larger capacity to move other objects. The larger and faster the wind is, the more energy or capacity it has to move things. For wind with the same fetch and duration, faster wind is stronger, has more energy, and can produce larger waves than slower wind.
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