This large clear self-bailing scupper mounts on your boat transom above water line and fits 1.5 to 3 inch openings, replacing old boat scupper flaps or flapper kits. Inside, a solid ball delivers one way scupper valve for boats action: water flows out through boat scuppers transom, but when waves push back, the ball seals instantly to block seawater from entering. It drains your boat deck drain automatically at rest or low speed, using water pressure to push the ball open. Built from marine grade polycarbonate with a solid polyethylene ball, it fights seawater, UV, and salt spray for lasting durability. The ball style design means no clogging, unlike scupper flapper hinges that trap debris, so leaves, seaweed, or small fish won't block your drain.