Luff

The leading edge, which is the part of the sail that faces the wind when the sail is set correctly.

The luff of a sail is a critical part of sailboat dynamics and sail trim. It is the forward-most edge of the sail, running from the head (top) of the sail down to the tack (bottom front corner).

On a mainsail, the luff is typically attached to the mast, while on a headsail (such as a jib or genoa), it is attached to the forestay. The luff is the part of the sail that first interacts with the wind and is crucial for determining the sail’s shape and efficiency.

In terms of sail shape, the tension along the luff is important for controlling the sail’s draft (the depth of the curve). More tension along the luff flattens the sail, useful in stronger winds to reduce heeling and maintain control. Conversely, easing the luff tension allows the sail to become fuller, which is advantageous in lighter winds to capture more power. On many boats, luff tension is adjusted using a device called a cunningham, which pulls down on the sail near the tack to increase tension.

The luff also plays a role in sail handling, particularly when hoisting or lowering the sail. For example, on a mainsail, the luff is raised by pulling the halyard, which pulls the sail up the mast. On a headsail, the luff is often rolled or furled around the forestay when the sail is not in use.

In summary, the luff is the forward edge of the sail. Proper attention to the luff helps ensure the sail is set correctly for the wind conditions, maximising the boat’s performance and efficiency.