A topping lift is a line or wire in a sailboat's standing or running rigging that runs from the masthead to the aft end of the boom, applying upward force to support the boom's weight. It keeps the boom from dropping into the cockpit or on deck when the mainsail is lowered or reefed.

Key Features and Functions:
Support & Protection: It holds the boom up when the sail is not in use, preventing damage to the boat or injury to crew.

Reefing Aid: It maintains boom height when the sail is shortened, allowing for easier reefing.

Adjustment: Often adjustable from the cockpit or mast to alter sail shape, it is typically secured by a cleat or rope clutch.

Materials: Frequently made of high-quality polyester or low-stretch, durable materials like Dyneema.

Alternative Support: On some boats, a rigid boom vang can eliminate the need for a topping lift.