Abstract: An adjustable roller furling spar includes an elongated base member which is securable on a sailboat and an adjustable periphery assembly which is attached to the base member and coextends a distance therewith. The periphery assembly is adjustable to define an effective winding cross-section of the spar which is variable along the longitudinal extent thereof and which is operable for windingly receiving a sail on the spar. By properly adjusting the periphery assembly, it is operable to compensate for irregular stretch in older sails when the spar is used for reefing so that even a badly stretched sail can be maintained in a substantially flat disposition.