In sailing, a following sea is a weather condition where the waves move in the same direction as the boat. In some circumstances, it can be hazardous, and sailors need to exercise caution. Following seas can also be beneficial, as sailors do not need to fight the waves while sailing, since the waves move with the boat. These conditions are easy to spot, as people can see the heading of the waves from the deck of the boat.
In a following sea, waves tend to roll under the boat. It can become risky when the swells are large, especially if a wind is pushing at the boat from behind. In these conditions, the boat may climb waves and then be driven down the other side, running the risk of swamping. Handling a boat in this kind of following sea requires closely controlling the amount of power to ride the backs of the waves without pitching into the troughs between them.
As people learn to sail crafts of all sizes, they will pick up information about how to work with waves and currents. This includes lessons on how to identify the direction of wave movement as well as tips on handling boats in high seas, choppy surf, and other adverse conditions. In the case of a following sea, sailors must learn to judge the most appropriate speed for the conditions so they work with the waves without endangering their boats. People also need to learn about the conditions appropriate for their boat and skill level, avoiding the water when it would not be safe to sail.
The movement of a boat in a following sea can vary, depending on the height and frequency of the waves. Experienced sailors may be able to feel the conditions from the boat's movement. Being in these conditions is usually a good sign, as it means the boat will move along at a fast clip with a minimal exertion of energy. When the waves are working against the boat, it is necessary to use more energy to fight them and maintain the proper heading.
These sailing conditions are referenced in the phrase “fair winds and following seas,” a traditional blessing among sailors in some regions of the world. The term implies optimal sailing conditions, where the winds move in the direction of travel, facilitating rapid, comfortable sailing, and the sea works with the boat rather than against it.