A pontoon boat is a flattish boat that relies on pontoons to float. These pontoons (also called tubes) contain a lot of reserve buoyancy and allow designers to create massive deck plans fitted with all sorts of accommodations, such as expansive lounge areas, stand-up bars, and sun pads. Better tube design has also allowed builders to put ever-increasing amounts of horsepower on the stern. Pontoon boat drafts may be as shallow as eight inches, which reduces risk of running aground and underwater damage. The pontoon effect is when a large force applied to the side capsizes a pontoon boat without much warning, particularly a top-heavy boat.
Common boat designs are a catamaran with two pontoons, or a trimaran with three. Boats with three pontoons are sometimes called tri-toons.