Fetch

The uninterrupted distance of open water over which wind blows in a broadly constant direction.

Fetch is measured along the upwind water surface available for wave generation, not as the path travelled by an individual parcel of air. Coastlines, islands, ice and major changes in wind direction can limit the effective fetch.

Wave growth depends on wind speed, duration and fetch together. Increasing any one can increase wave height and period until another factor becomes limiting, while depth, current and pre-existing swell can modify the sea observed at the vessel.