Abstract: A mainsail furling device for a sailboat having a boom comprising a plurality of pairs of mounting brackets attached to the boom, each of the mounting brackets having a substantially L-shaped cross section and two connected approximately rectangular bracket panels, a substantially flat mainsail retaining arm pivotally attached to each mounting bracket pivotable between a position folded against the boom and a deployed position substantially perpendicular to the boom, a device for pivotally mounting each mainsail retaining arm on its mounting bracket comprising a threaded bolt and nut and a device for securing each of the mainsail retaining arms in its deployed position substantially perpendicular to the boom.