16 - Bottom structure

Abstract

This chapter focuses on the bottom structures of the ships. There are two types of bottom structures that are mainly used in all the ships. These structures are single bottom structure and double bottom structure. In smaller ships having single bottoms, the vertical plate open floors are fitted at every frame space and are stiffened at their upper edge. A centre line girder is fitted, and one side girder is fitted on each side of the centre line where the beam is less than 10 m. Where the beam is between 10 and 17m, two side girders are fitted, and if any bottom shell panel has a width to length ratio greater than four, additional continuous or intercostal stiffeners are fitted. The continuous centre and intercostal side girders are stiffened at their upper edge and they extend as far forward and aft as possible. In a double bottom structure, an inner bottom may be provided at a minimum height above the bottom shell, and maintained watertight to the bilges. This provides a considerable margin of safety because in the event of bottom shell damage, only the double bottom space may be flooded. The space is not wasted but utilized to carry oil fuel and fresh water required for the ship, as well as providing ballast capacity. The minimum depth of the double bottom in a ship will depend on the classification society's requirement for the depth of centre girder. It may be deeper to give the required capacities of oil fuel, fresh water, and water ballast to be carried in the bottom.