Cargo ships are necessary for world commerce. There are two basic kinds of cargo ships: freighters and tankers. Freighters come in all shapes and sizes in order to accommodate various loads. Dry cargo vessels comprise one category and are used to transport coal, grain, iron ore, and similar products that can be loaded in bulk. The first of these hauled iron ore on the Great Lakes during the late 1800s; it resembled a long steel box, with crew quarters at the front and engine at the back. Modern freighters, by contrast, have a double hull for strength and safety, and include storage areas for fuel oil, water ballast, or fresh water. The largest of these in use today, with the bridge and engine room near the tail, can haul over 100,000 tons of cargo. Barges are smaller forms of these bulk carriers. Formerly powered by sail, they...