A crew of 2,200 on the Symphony of the Seas tends to more than 5,500 passengers as they sail to ports in Spain, France and Italy.

Viking Long Ship Gefjon visits the great cities of the Danube, Main and Rhine Rivers but the crew must navigate through 67 locks, and face bridges only a few centimetres higher than the ship and river beds that narrow to tight channels.

The crew of the world's largest river-cruising company takes to the waters of the ocean-cruising industry, navigating narrow passages and rough seas around Spain, Normandy and Amsterdam.

The crew of the Marina, Oceania Cruises' largest ship, makes a 12-day, five port voyage.

The crew of the Regal Princess, Princess Cruises' largest ship, faces narrow channels, shifting waters, shallow harbours, and transport vehicles.

Koningsdam is Holland America's newest, largest and most technologically advanced ship; sailing the narrow Norwegian fjords on a mega-ship presents numerous challenges for the bridge team.