Contribution of Superstructures to the Righting of Ships

Abstract

Contribution of superstructures having various and different degree of watertightness to the righting of a ship lurching among lateral waves is studied experimentally. According as unit superstructures of box type, even though of non-watertight, are added one on a cylindrical model ship, the model rocovers from the lurch, otherwise it capsizes. Corresponding to watertightness of the unit, there is a certain boundary in the total volume of superstructures at which whether it is capsized or not is distinctly distinguished. Capsizing or not is interpreted enough in words of energy balance. The bounding volume determined from energy balance also coincides with the one from experiment. The bounding volume, of course, inereases to some extent if the watertightness falls. The time required up to capsizing from oncoming of the first wave is shortened more or less for weaker tightness. If a proper volume is chosen, however, the superstructure will contrilbute to rescue the ship from a crisis of capsizing, even when it is not watertight.