A downrigger is a device used while fishing using the trolling method, which places a lure at the desired depth. A downrigger consists of a three to six-foot horizontal pole which supports a cannonball (large weight) by a steel cable (generally stainless steel). A clip, also known as a "release" attaches a fishing line to the cannonball weight. The bait or lure is attached to the release.
Read more about Downrigger: Operation of A Downrigger, Brief History