Abstract: A folding pontoon boat which can be folded to a lesser width unfolded to a greater operating width. The boat can be launched in the folded configuration, unfolded on the water, and subsequently refolded to the reduced width on the water. The boat comprises pontoons, deck members, jamb plates at the inner sides of the deck members, and a hinge connecting inner sides of the deck members to each other. The jamb plates provide sufficient structure that the deck members are self-supporting and can support normal deck loading at the hinge without additional superstructure above the deck to support the hinge structure. A motor mount at the rear of the boat maintains a constant orientation as the boat is folded and unfolded between the reduced width configuration and the greater width configuration.