A Downrigger is a device used in trolling applications that has a wheel which holds upwards of 150 feet of cable.  The cable is connected to a downrigger ball that is tied to the fishing line which pulls the lure down into deep water.  Most downrigger balls are between 5 and 10 pounds and the line is attached to the ball with a quick release clip that frees the line from the ball when a fish strikes.