Abstract: A semi-automatic boiler plug assembly having a mounting plate with a central hole aligned with a bailer hole on a boat transom is described. Attached to the mounting plate is a cylinder and piston therein made of a resilient material which seats in the central hole of the mounting plate in a closed position. Two arms extending to either side of the piston, and through slots on opposite sides of the cylinder, guide the piston in its travel back and forward in the cylinder. Immediately behind the piston is a spring to bias the piston forward in the cylinder toward the closed position. On the outside of the cylinder are two hinge plates attached to the piston by guide arms and by hinge pins that pass through a hole in the hinge plates and into the piston guide arms. Formed onto the outboard side of the hinge plates are hollow chambers which form floats.

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.