Bailing is the process of removing water from a vessel.
A hand bailer is a device used for manually removing water which has entered a boat. In the simplest case, it is merely a container which can be filled and then emptied. This kind of device is in use since early times. It is still in use on small boats and rafts, which may benefit from a self bailer. Some regulations require either or both as mandatory equipment.
For some modern types of dinghys in sailing sports hand bailers can be obsolete when they are equipped with self bailers, sometimes also called automatic bailers. Self-bailing boats are shaped so that they will drain completely if filled with water; powered by the venturi effect and the motion of the boat, they are distinct from the powered bilge pumps used on non-self-bailing boats.