A layline is an imaginary line extending from a racing mark (buoy) that represents the optimal course a sailboat can take on a single tack to reach that mark. When a boat reaches this line, it can "fetch" the mark without further tacking or jibing. There are two laylines—port and starboard—for every mark.

Upwind Sailing: Laylines indicate the furthest point you can sail before tacking to reach the windward mark efficiently.

Downwind Sailing: They indicate the optimal line to jibe toward the leeward mark.

Risks of Early Arrival: Arriving on a layline too early (a "long-range layline") is often considered a mistake, as it reduces tactical flexibility and limits your ability to react to wind shifts.

Variables: Laylines are not static; they change based on wind direction, current, and boat performance.

Navigation Tools: Electronic navigation systems, like those from Garmin and TimeZero, can calculate and display laylines (green for port, red for starboard) to aid in tactical decisions.

"Laying the mark" means you are currently on a course that will take you around the buoy.