Abstract: A safety capsule structure comprising semi-cylindrical half-sections provided with yieldable and buoyant lining secured on the inner periphery thereof, the half-sections being adapted for installation in a boat hull, or the like, for stabilization of the boat structure against capsizing and to provide a flotation force for the boat, the half-sections being further adapted to be secured together along a common longitudinal side edge to provide alternate open and closed positions with respect to a pair of the half-sections, the closed position of the half-sections providing a protective capsule for an occupant for protection of the occupant during hazardous ambient conditions, such as a tornado, or the like.