Patent ID: 7789031

Claim:
A double-hulled vessel whose ballast draft line is previously set at an empty state thereof, comprising: an outer hull formed on bottom and side portions of the vessel by two outer side shells and a bottom outer shell; an inner hull formed on bottom and side portions of the vessel within the outer hull by two inner side shells and a inner bottom shell; a plurality of cross bulkheads traversing the vessel in a lateral direction, a plurality of tank bulkheads positioned between the inner and outer bottom shells near the side of vessel along the length thereof; a plurality of cargo tanks formed by two bulkheads, two inner side shells and the inner bottom shell; a plurality of side tanks positioned near the side of the vessel between the inner and outer hull formed by two cross bulkheads, inner and outer side shells and a tank bulkhead; a plurality of bottom tanks positioned near the bottom of the vessel formed by two tank bulkheads and inner and outer bottom shells; a plurality of side air tubes, which can be expanded or contracted, having openings for air flow, being positioned within each side tank of the vessel, and capable of containing air to substantially fill the entire space of each side tank, when the vessel is loaded with cargo; a plurality of side seawater tubes, which can be expanded or contracted, having openings for seawater flow, being positioned underneath the side air tubes within each side tank of the vessel, and capable of containing seawater to substantially fill the space in each side tank from the bottom portion of the vessel and up to the ballast draft line, when the vessel is not loaded with cargo; a plurality of bottom air tubes, which can be expanded or contracted, having openings for air flow, being positioned within each bottom tank of the vessel, and capable of containing air to substantially fill the entire space of each bottom tank, when the vessel is loaded with cargo; a plurality of bottom seawater tubes, which can be expanded or contracted, having openings for seawater flow, being positioned underneath the bottom air tubes within each bottom tank of the vessel, and capable of containing seawater to substantially fill the space in each bottom tank when the vessel is not loaded with cargo; and a plurality of seawater holes formed in the outer bottom shell to be connected to the side and bottom seawater tubes to allow the flow of seawater; wherein the preset ballast draft line is maintained by regulating the air supply to air tubes within the side and bottom tanks, which supply causes the expansion and contraction of the air tubes, which, in turn, causes the corresponding contraction and expansion of the seawater tubes to regulate the amount of seawater contained therein.