In sailing, an obstruction is any object, area, or line—such as a mooring, shoal, or shore—that a boat cannot safely pass without making a substantial course change when one hull length away. Objects passable only on one side or designated by sailing instructions are also obstructions, triggering rules for room to pass.

Key Aspects of Obstructions in Racing Rules (RRS):
Definition: An object requiring a significant course change (usually) if approached head-on, or an object that can only be passed safely on one side.

Examples: A pier, a moored vessel, shallow water, or a restricted zone.

Continuing Obstruction: An obstruction that takes significant time to pass, such as a shoreline, where a boat passes alongside for at least three of her hull lengths.

Rule 19 (Room at Obstructions): Governs how boats interact when passing an obstruction. If two boats are passing, the outside boat must give the inside boat room to pass.

Exceptions: A boat actively racing is generally not an obstruction to others, unless it is capsized, anchored, or aground.