A jetty is a long, narrow, man-made structure that extends from the shore into a body of water (sea, lake, or river). Typically built from wood, stone, concrete, or steel, jetties are designed to manage water flow, protect shorelines, and aid in navigation.

Key Aspects of a Jetty in Sailing:
Harbor Protection: Jetties function as barriers, often built in pairs at the entrance to a harbor or river to protect the channel from storm waves, currents, and crosscurrents.

Erosion Control: They prevent beaches from washing away by acting as a barrier to sediment movement (littoral transport).

Channel Maintenance: Jetties "train" or confine the water flow, creating faster currents that help scour away sediment, preventing the mouth of a river or harbor from becoming shallow (shoaling).

Landing Facility: They serve as structures where boats can dock or moor, allowing passengers to get on/off and facilitating the loading/unloading of goods.