Unfurl in sailing refers to the action of opening, unrolling, or spreading out a sail (such as a jib, genoa, or mainsail) from its rolled or stowed position around a boom, mast, or forestay. It is the reverse of furling and is done to expose the sail to the wind for power.

Key Aspects of Unfurling:
Action: Involves releasing the furling line (or furler) while easing out the sail sheet, allowing the sail to pull out and extend.

Method: To prevent the furling line from creating a "bird's nest" in the drum, control the speed of the unfurling by keeping tension on the line, sometimes using a winch if necessary.

Safety: It is commonly done with the boat on a broad reach or downwind to reduce wind pressure on the sail during deployment.

Usage: It refers specifically to opening roller-reefing systems on modern boats to deploy the headsail or main.

Unfurling essentially transforms a securely stowed, rolled-up sail into an active sail capturing wind power.