A Capstan is a vertical rotating drum on an axle turned by wooden bars inserted into holes along the top of the capstan which is turned by crewmen. The capstan is used to weigh, or raise the anchor. Since the anchor cable is large and does not bend easily, it is usually is drawn by a messenger which is then wrapped about the capstan.
It can also be used to raise yards and spars into position.
Not to be confused with a windlass, which is a similar machine on a horizontal axis.
- Capstan at Wikipedia.