Abstract: A channel-shape sweep line retainer extends along the leading front edge of an elevating fin, with the open side of the retainer facing the trailing rear edge of the fin. Extending across the fin at the open side of the retainer is a bar mounted on the fin for movement toward and away from the retainer, but normally locked in its forward position by a pair of laterally spaced arms extending rearwardly away from the bar with their front ends engaging it. The rear ends of the arms are pivotally connected to the fin so that when arm-positioning spring means between the arms and connected to them are pulled rearwardly, the front ends of the arms will be swung inwardly toward each other out of engagement with the bar, whereupon the bar can be retracted to open the retainer for admission or release of a sweep line.