Fetch

The fetch is the distance at sea or on a water level to the top of which breath a wind given without meeting obstacle (a coast) from the place where it is created or from a coast if it comes from the ground.

This concept makes it possible to include/understand the height of the waves and the swell at a given place. All things being equal in addition, plus the fetch is important plus the height of the waves will be large. A contrario, safe from a coast (under the wind of a coast), the height of the waves will be very low, even if the wind is very strong because the fetch is smaller there.

The practical use of the fetch for the calculation of the state of sea is however rather delicate, because the height of the waves depends also much on the angle of the wind compared to the coast, and the geometry of the generating surface. Thus, with less few kilometers of the coast the waves can be propagated with more 60° of the direction of the wind, and one can even observe a sea of the wind crossed, with trains of vague courts in the direction of the longer wind, and the trains of waves being propagated along the coast. Indeed, as soon as the wind is oblique compared to the coast the waves being propagated in the direction of the coast have a larger fetch and thus more energy than the waves being propagated in the direction of the wind.

See too

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