A ringtail a sail which is set abaft (behind) a fore-and-aft sail to increase the total sail area of a sailing vessel in light winds.
It exists in two forms. The older and more common type is a quadrilateral sail set on spars which extend the gaff and boom of a gaff sail. The effect is as if the gaff sail were larger in size, with the extra sail cloth of the ringtail continuing the plane in which the gaff sail is set.
The other version of the ringtail is a triangular sail. It is used in conjunction with a triangular (or "leg-of-mutton") working sail (as opposed to a quadrilateral gaff sail). It is set both above and abaft the working sail; the head of the ringtail is hoisted to the top of the topmast, and the clew is sheeted down to the end of the boom of the working sail. The luff runs parallel to the topmast, to which it is usually laced. The foot approximately follows the line of the luff of the leg-of-mutton sail with which it is set. This version's intent was to provide extra sail area with the minimum amount of extra work for a small crew. It could be found on the mizzen of coasting craft, being particularly common on the schooners of the American West Coast towards the end of the 19th century.: 83–84 : 128