An additional chamber to watercraft that adds both volume and curvature to other compartments or components of the watercraft that are essentially flat is described. The additional chamber provides for modular construction of watercraft for creating volumetric space as well as a curved surface to the outer portion of the watercraft. The chamber advantageously increases the aesthetic appeal of the watercraft as well as provides a surface on which water is discouraged from pooling or collecting on. Various watercrafts having such a chamber are also described.