Abstract: A boat structure including an oblong central body, two pontoons, two longitudinal lateral arms of which a first of their extremities is integral with said body by first attachment members and two second and third linking members of the two other second extremities of the arms are attached, respectively, to one of the two pontoons. The body includes a beam comprising two parts abutting one against the other along a junction surface, a first relatively short part substantially in the shape of the arc of a circle with a first value R1 for the radius of curvature and a second part longer than the first part, in the shape substantially of the arc of a circle with a second value R2 for the radius of curvature significantly greater than the first value R1.