1) Dry cargo ships=freighter - ship or vessel that carries cargo, goods, and materials from one port to another)
a) Bulk carriers - is ocean-going vessel used to transport bulk cargo items such as iron ore, bauxite, coal, cement, grain and similar cargo.
b) Container ships - cargo ships that carry all of their load in truck-size containers.
2) Tankers - ship designed to transport liquids in bulk.
3) Specialized ships - heavy lift goods or refrigerated cargo (Reefer ships), roll-on/roll-off cargo (RoRo) ships for vehicles and wheeled machinery.
4) Coasters - smaller ships for any category of cargo which are normally not on ocean-crossing routes, but in coastwise trades.
5) Passenger ships - ship whose primary function is to carry passengers.
a) Cruise ship=Cruise liner - passenger ship used for pleasure voyages, where the voyage itself and the ship's amenities are considered an essential part of the experience.
b) Ferries - a form of transportation, usually a boat or ship, but also other forms, carrying (or ferrying) passengers and sometimes their vehicles.
Source: http://en.wikipedia.org/wiki/Merchant_ship
