Tanker for the prevention of cargo oil spillage

A tanker comprising:

• a ship body having side walls and a bottom;
• a plurality of cargo oil tanks arranged in an interior of said ship body;
• double-sidewall hull constructions arranged on opposite sides of said cargo oil tanks to prevent outflow of cargo oil from said cargo oil tanks to outside of said side walls;
• each double-sidewall hull construction comprising an inner hull formed by said tank side walls and a horizontal flat portion connected between said lower ends of said side walls of said upper cargo oil tanks and said upper ends of said side walls of said lower cargo oil tanks, said flat portion being disposed at substantially the same height from said bottom as said mid-height deck, so that each double sidewall has a width at said lower ends of said side walls of said upper cargo tanks less than the width of each double sidewall at said upper ends of said sidewalls of said lower cargo tanks;
• and
• a mid-height deck arranged to divide said cargo oil tanks into upper cargo oil tanks and lower cargo oil tanks;
• said mid-height deck having a highest position in a direction of height measured from said bottom determined to be lower than a position at which the following two pressures are equalized:
• pressure of cargo oil exerted on said bottom when each lower cargo oil tank is filled with cargo oil from said bottom to the position of said mid-height deck under a condition of minimum ship draft as the tanker cruises with a cargo oil in said cargo oil tanks, and
• pressure of sea water exerted on said bottom.