Abstract: A semi-automatic bailer plug assembly for attachment to the transom of a boat having a bail hole therein for receiving the bailer plug assembly is described. The bailer plug is normally spring biased into a closed position to plug the bail hole until it is manually retracted by a plunger disposed in opposition to the spring. When the plunger is pulled back and the boat transom is out of the water, a pair of stop members engage the plug and hold the plug in an open position permitting the boat to be drained of water. The stop members are coupled to a pair of float members. When the transom of the boat is placed in the water a buoyant force acting against the floats releases the spring biased plunger from engagement with the stop members and permits the bailer plug to automatically close the bail hole in the boat transom.