A forestay (or headstay) is a vital piece of standing rigging on a sailboat, typically a stainless steel wire or rod running from the masthead (or upper mast) down to the bow. Its primary functions are supporting the mast to prevent it from falling backward, acting as the forestay anchor for headsails (jib or genoa), and managing rig tension.

Key Aspects of a Forestay:
Support: It acts as the forward counterbalance to the backstay.

Headsail Attachment: Headsails are secured to the forestay using hanks or a furling system (a foil covering the wire).

Tension: Proper tension in the forestay ensures correct sail shape for upwind performance and keeps the mast upright.

Types: While usually permanent, some boats feature a removable "inner forestay" to set a heavy-weather jib closer to the mast.

Connection: It attaches to the bow via a turnbuckle to allow tension adjustments.