An anchor is a heavy object, often made out of metal, that is used to attach a ship to the bottom of a body of water at a specific point. There are two primary classes of anchors—temporary and permanent. A permanent anchor is often called a mooring, and is rarely moved; it is quite possible the vessel cannot hoist it aboard but must hire a service to move or maintain it. A temporary anchor is usually carried by the vessel, and hoisted aboard whenever the vessel is under way; it is what most non-sailors mean when they refer to an anchor. A sea anchor is a related device used when the water depth makes using a mooring or temporary anchor impractical. The hole through which an anchor rope passes is known as a hawsepipe.