Since the dawn of history, boats have been used in rivers and ship have been used to cross seas and oceans, to carry goods and people from one place to another. The volume of cargo carried by ships continues to increase, and ships become larger and faster. For this reason, many ships are built for particular cargoes. Tankers carry liquid cargo such as petroleum, refrigerated cargo is carried in reefers. Other ships, called bulk-carries, carry certain cargoes such as iron ore, grains or timber in bulk. Many vessels are built for certain duties: tugs for towing ships, dredgers for deepening channels, and specialist crafts such as gas carriers, ice- breaker and floating cranes. New types of ships include container vessels and Ro-ro ships. Container vessels carry large cases, or containers of a wide variety of goods. They have a high service speed and can be loaded and discharged very rapidly. “Ro-ro” ship have doors in their bows and sterns. Although there is a wide variety of ships at the present time, more new designs are expected. . Since the dawn of history, boats have been used in rivers and ship have been used to cross seas and oceans, to carry