Abstract: A tiedown device and system, particularly suited for releasably securing a boat cover to a boat frame, is disclosed. The device has a hook-like end fastening member to whch an end of a flexible, extensible cord of a selected length is secured. The end fastening member has an inturned end portion that forms a restricted opening or passage into the inside of the end fastening member through which the cord extends and is returned to form a first fastening loop. The other free end of the cord is secured so as to apply a selected tension to the cover as by using a knot. A set of tiedown devices in the tiedown system applies uniform tension to a boat cover or the like.