A hatch is a horizontal, generally rectangular opening in a boat’s deck, serving as a doorway, window, or loading access to lower compartments. They provide ventilation and access to cabins or storage while maintaining a watertight seal using latches (dogs) to prevent water intrusion.

Key Characteristics:
Location: Usually located on horizontal deck surfaces, whereas doors are vertical.

Function: Provides access for people, cargo, or airflow, and must be durable and waterproof.

Watertight: They are meant to be closed securely—"battened down"—when navigating rough seas to prevent flooding.

Components: Consists of a hatchway (opening) and the cover itself.

Related Terms: "Down the hatch" originated from lowering cargo, and "batten the hatches" refers to securing them.