Abstract: A modular watercraft assembly and apparatus. In one embodiment, the watercraft assembly includes a divided floatation support member that provides buoyant support. The divided floatation support member includes a first pontoon and a second pontoon that are both longitudinally extensible pontoons. The longitudinally extensible pontoons each include at least two substantially rigid tubes that are telescopically extensible and collapsible in an annularly nested manner. The assembly further includes multiple substantially rigid cross members and multiple cross member fasteners for transversely coupling the cross members between the first and second pontoons of the divided floatation support member. When assembled the watercraft assembly provides buoyant support for a variety of different craft designs including but not limited to a sailing catamaran, a pedaloe, and others.