Portugal's Mystic Cruises has boosted its series of polar expedition cruiseship newbuildings to seven.
Industrial group Martifer SGPS said its Portuguese shipbuilding subsidiary West Sea Estaleiros Navais had agreed a deal for four more ice-class Explorer vessels worth €286.7m ($319m).
The 9,300-gt, 200-berth units will have a hybrid propulsion system and will carry 112 crew.
