The luff is the forward-most, leading edge of a sailboat sail, extending from the top (head) to the bottom forward corner (tack). It faces the wind first and is typically attached to the mast (mainsail) or forestay (jib). Luff tension controls the sail's draft, with tighter tension flattening the sail in stronger winds.

Key Aspects of the Luff:
Function: Defines the sail’s entry shape and interacts directly with the wind.

Attachment: On a mainsail, it is held to the mast via slides, a bolt rope, or a groove. On a jib, it is attached to the forestay.

Tension Control: Controlled by the halyard and the Cunningham, which adjust the tension along the front edge to manage sail draft.

Components: Includes the tack (bottom-front corner) and the head (top corner).

Luffing: If the luff is eased too much, or the boat points too high, the sail will shake, a condition known as "luffing".

The luff is essential for controlling the sail's power and performance, with tighter tension used to flatten the sail for stronger winds and looser for lighter wind.