Semi-submersible vessel having a sealed closed chamber of truncated ovoid shape

A semi-submersible vessel comprising one module formed by a sealed closed chamber, completely submerged in normal use, provided with ballast, means for varying said ballast, a support structure secured to the chamber, said structure being partially immersible in use, and a horizontal deck carried by the upper portion of the support structure wherein at least the lower portion of the vessel formed by the closed chamber has the form of a shell having the ellipsoidal shape of an egg with a pointed end and a less pointed end and being truncated along a plane perpendicular to the longitudinal axis, to retain the less pointed portion thereof and to eliminate the more pointed portion of the shell, wherein the lower portion of the vessel formed by the closed chamber opens at its upper portion toward the support structure and at its lower portion through an opening for communication with the liquid environment, said shell having an external and an internal curved wall such that the majority of their respective surfaces is close to a spherical surface whereby the lines of action of the great majority of the hydrostatic forces acting on said surface traverse a zone which surrounds its geometric center, the volume of said zone being small in comparison to the total volume circumscribed by said surface.