On a

square rig Square rig is a generic type of sail plan, sail and rigging arrangement in which a sailing ship, sailing vessel's primary driving sails are carried on horizontal spar (sailing), spars that are perpendicular (or wikt:square#Adjective, square) to t ...

ged ship, the spanker is a gaff-rigged fore-and-aft sail set from, and aft of, the aftmost mast. Spankers are also called ''driver'', ''jigger'', and ''pusher'' sail. On a schooner of four or more masts, the spanker is the sail on the mast nearest the stern. The spanker is a small sail, but as it is so far aft of the balance point of the hull, it has strong leverage. When sheeted in, the spanker is important in driving the boat to a new tack.

References

Sailing rigs and rigging {{Water-transport-stub