Sea routes are determined by where cargo is found. These large ferries allow vehicles to drive on and off. Bulk Carriers have large cargo holds, suitable for coal and grain. Gas Carriers transport liquid gas in pressurized or refrigerated tanks. These ships can carry up to four thousand containers which hold everything from furniture to toys.
Barges take cargo from main seaports and terminals to final destinations inland.
Navigation Early sailors used the sun and stars to navigate. Navigation today has been simplified by the invention of electronic aids. Radar and sonar locate other ships and underwater hazards. Using a sonic depth finder , the luxury cruise ship monitors the depth of the water. Satellites beam radio signals to earth, improving communication between ships and land.